diff --git a/lld/ELF/Arch/ARM.cpp b/lld/ELF/Arch/ARM.cpp
--- a/lld/ELF/Arch/ARM.cpp
+++ b/lld/ELF/Arch/ARM.cpp
@@ -6,10 +6,14 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "InputFiles.h"
+#include "OutputSections.h"
+#include "SymbolTable.h"
 #include "Symbols.h"
 #include "SyntheticSections.h"
 #include "Target.h"
 #include "lld/Common/ErrorHandler.h"
+#include "lld/Common/Filesystem.h"
 #include "llvm/BinaryFormat/ELF.h"
 #include "llvm/Support/Endian.h"
 
@@ -19,6 +23,7 @@
 using namespace llvm::ELF;
 using namespace lld;
 using namespace lld::elf;
+using namespace llvm::object;
 
 namespace {
 class ARM final : public TargetInfo {
@@ -908,6 +913,403 @@
   }
 }
 
+// Initialize this->symbols. this->symbols is a parallel array as
+// its corresponding ELF symbol table.
+template <class ELFT> void ObjFile<ELFT>::importCmseSymbols() {
+  ArrayRef<Elf_Sym> eSyms = this->getELFSyms<ELFT>();
+  numSymbols = eSyms.size();
+  symbols = std::make_unique<Symbol *[]>(numSymbols);
+
+  // Error for local symbols. The symbol at index 0 is LOCAL. So skip it.
+  for (size_t i = 1, end = firstGlobal; i != end; ++i) {
+    error("CMSE symbol " + CHECK(eSyms[i].getName(stringTable), this) +
+          " in import library " + toString(this) + " is not global");
+  }
+
+  for (size_t i = firstGlobal, end = eSyms.size(); i != end; ++i) {
+    const Elf_Sym &eSym = eSyms[i];
+    Defined *sym = reinterpret_cast<Defined *>(make<SymbolUnion>());
+
+    // Initialize symbol fields.
+    memset(sym, 0, sizeof(Symbol));
+    sym->setName(CHECK(eSyms[i].getName(stringTable), this));
+    sym->value = eSym.st_value;
+    sym->size = eSym.st_size;
+
+    if (eSym.st_shndx != SHN_ABS) {
+      error("CMSE symbol " + sym->getName() + " in import library " +
+            toString(this) + " is not absolute");
+      continue;
+    }
+
+    if (!(eSym.st_value & 0x1)) {
+      error("CMSE symbol " + sym->getName() + " in import library " +
+            toString(this) + " is not a Thumb code symbol");
+      continue;
+    }
+
+    if (eSym.getType() != STT_FUNC) {
+      error("CMSE symbol " + sym->getName() + " in import library " +
+            toString(this) + " is not of function type");
+      continue;
+    }
+
+    if (symtab.cmseImportLib.find(sym->getName()) !=
+        symtab.cmseImportLib.end()) {
+      error("CMSE symbol " + sym->getName() +
+            " is multiply defined in import library " + toString(this));
+      continue;
+    }
+
+    if (eSym.st_size != ACLESESYM_SIZE) {
+      warn("CMSE symbol " + sym->getName() + " in import library " +
+           toString(this) + " does not have correct size of " +
+           Twine(ACLESESYM_SIZE) + " bytes");
+    }
+
+    symtab.cmseImportLib[sym->getName()] = sym;
+  }
+}
+
+// Check symbol attributes of the acleSeSym, sym pair.
+// Both symbols should be global/weak Thumb code symbol definitions.
+static std::string checkCmseSymAttributes(Symbol *acleSeSym, Symbol *sym) {
+  Defined *a = dyn_cast_or_null<Defined>(acleSeSym);
+  if (!a)
+    return (toString(acleSeSym->file) + ": cmse special symbol '" +
+            acleSeSym->getName() + "' is not defined")
+        .str();
+
+  if (!a->isFunc() || (a->value & 1) != 1)
+    return (toString(a->file) + ": cmse special symbol '" + a->getName() +
+            "'; is not a Thumb function definition")
+        .str();
+
+  if (a->section == nullptr)
+    return (toString(a->file) + ": cmse special symbol '" + a->getName() +
+            "'; cannot be an absolute symbol")
+        .str();
+
+  Defined *s = dyn_cast_or_null<Defined>(sym);
+  if (!s)
+    return (toString(s->file) + ": cmse entry function '" + s->getName() +
+            "'; is an undefined symbol")
+        .str();
+
+  if (!s->isFunc() || (s->value & 1) != 1)
+    return (toString(s->file) + ": cmse entry function '" + s->getName() +
+            "'; is not a Thumb function definition")
+        .str();
+
+  if (s->section == nullptr)
+    return (toString(s->file) + ": cmse entry function '" + s->getName() +
+            "'; cannot be an absolute symbol")
+        .str();
+
+  return "";
+}
+
+// Look for [acle_se_<sym>, <sym>] pairs, as specified in the Cortex-M Security
+// Extensions specification.
+// 1) <sym> : A standard function name.
+// 2) acle_se_<sym> : A special symbol that prefixes the standard function name
+// with __acle_se_.
+// Both these symbols are Thumb function symbols with external linkage.
+// <sym> may be redefined in .gnu.sgstubs.
+void elf::processArmCmseSymbol() {
+  if (!config->cmseImplib)
+    return;
+
+  // Only symbols with external linkage end up in symtab, so no need to do
+  // linkage checks. Only check symbol type.
+  for (Symbol *acleSeSym : symtab.getSymbols()) {
+    if (!acleSeSym->getName().startswith(ACLESESYM_PREFIX))
+      continue;
+
+    if (!config->armCMSESupport)
+      error("cmse special symbol '" + acleSeSym->getName() +
+            "' only allowed for ARMv8-M architecture or later");
+
+    // Try to find the associated symbol definition.
+    // Symbol must have external linkage.
+    StringRef name = acleSeSym->getName();
+    name.consume_front(ACLESESYM_PREFIX);
+    Symbol *sym = symtab.find(name);
+
+    if (!sym) {
+      error(toString(acleSeSym->file) + ": cmse special symbol '" +
+            acleSeSym->getName() +
+            "' detected, but no associated entry function definition '" + name +
+            "' with external linkage found");
+      continue;
+    }
+
+    std::string errMsg = checkCmseSymAttributes(acleSeSym, sym);
+    if (!errMsg.empty()) {
+      error(errMsg);
+      continue;
+    }
+
+    // <sym> may be redefined later in the link in .gnu.sgstubs
+    symtab.addCmseSymPair(acleSeSym, sym);
+  }
+
+  // If there is an unresolved definition for sym, resolve it using
+  // the definition in the import library.
+  for (auto &p : symtab.cmseImportLib) {
+    Defined *sym = p.second;
+    Symbol *d = symtab.find(sym->getName());
+    if (!d || dyn_cast_or_null<Defined>(d))
+      continue;
+    d->resolve(*sym);
+  }
+}
+
+ArmCmseSGSection::ArmCmseSGSection()
+    : SyntheticSection(llvm::ELF::SHF_ALLOC | llvm::ELF::SHF_EXECINSTR,
+                       llvm::ELF::SHT_PROGBITS,
+                       /*alignment=*/32, ".gnu.sgstubs") {
+  this->entsize = ACLESESYM_SIZE;
+  // The range of addresses used in the CMSE import library should be fixed.
+  for (auto &p : symtab.cmseImportLib) {
+    Defined *sym = p.second;
+    if (sym->value < impLibMinAddr)
+      impLibMinAddr = sym->value;
+    if (impLibMaxAddr <= sym->value)
+      impLibMaxAddr = sym->value + sym->size;
+  }
+  if (symtab.cmseSymVector.empty())
+    return;
+  std::sort(
+      symtab.cmseSymVector.begin(), symtab.cmseSymVector.end(),
+      [](std::pair<Symbol *, Symbol *> a, std::pair<Symbol *, Symbol *> b) {
+        return a.second->getName() < b.second->getName();
+      });
+  addMappingSymbol();
+  for (const auto &[acleSeSym, sym] : symtab.cmseSymVector)
+    addSGVeneer(acleSeSym, sym);
+}
+
+void ArmCmseSGSection::addSGVeneer(Symbol *acleSeSym, Symbol *sym) {
+  entries.push_back(std::make_pair(acleSeSym, sym));
+  if (acleSeSym->file != sym->file ||
+      cast<Defined>(*acleSeSym).value != cast<Defined>(*sym).value) {
+    // Symbol addresses different, nothing to do.
+    return;
+  }
+  // Only secure symbols with values equal to that of it's non-secure
+  // counterpart needs to be in the .sg.stubs section.
+  ArmCmseSGVeneer *ss = nullptr;
+  if (symtab.cmseImportLib.find(sym->getName()) == symtab.cmseImportLib.end()) {
+    ss = make<ArmCmseSGVeneer>(sym, acleSeSym);
+    newEntries += 1;
+  } else {
+    Defined *impSym = symtab.cmseImportLib[sym->getName()];
+    ss = make<ArmCmseSGVeneer>(sym, acleSeSym, impSym->value);
+  }
+  ss->parent = this;
+  this->sgSections.push_back(ss);
+}
+
+void ArmCmseSGSection::writeTo(uint8_t *buf) {
+  for (auto *s : this->sgSections) {
+    auto off = s->outSecOff - getVA();
+    s->writeTo(buf + off);
+  }
+}
+
+inline void ArmCmseSGSection::addMappingSymbol() {
+  addSyntheticLocal("$t", STT_NOTYPE, /*off=*/0, /*size=*/0, *this);
+}
+
+size_t ArmCmseSGSection::getSize() const {
+  if (sgSections.empty())
+    return (impLibMaxAddr ? impLibMaxAddr - getVA() : 0) +
+           (newEntries * entsize);
+
+  return entries.size() * entsize;
+}
+
+void ArmCmseSGSection::finalizeContents() {
+  if (this->sgSections.empty())
+    return;
+
+  auto it = std::stable_partition(
+      this->sgSections.begin(), this->sgSections.end(),
+      [](auto *i) { return i->getAddr() != std::nullopt; });
+
+  std::sort(this->sgSections.begin(), it, [](auto *a, auto *b) {
+    return a->getAddr().value() < b->getAddr().value();
+  });
+
+  // This is the partition of the veneers with fixed addresses.
+  uint64_t addr = (*this->sgSections.begin())->getAddr() == std::nullopt
+                      ? getVA()
+                      : (*this->sgSections.begin())->getAddr().value();
+  // Check if the start address of '.gnu.sgstubs' correspond to the
+  // linker-synthesized veneer with the lowest address.
+  if ((getVA() & ~1) != (addr & ~1)) {
+    error("start address of '.gnu.sgstubs' is different from previous link");
+    return;
+  }
+
+  for (auto *s : this->sgSections) {
+    if (s->getAddr() == std::nullopt)
+      break;
+    s->outSecOff = s->getAddr().value() & ~1;
+    Defined(s->file, StringRef(), s->sym->binding, s->sym->stOther,
+            s->sym->type, (s->outSecOff - getVA()) | 1, this->entsize, this)
+        .overwrite(*s->sym);
+  }
+  // This is the partition of veneers newly synthesized by the linker.
+  size_t off = std::max(getVA(), impLibMaxAddr);
+  for (auto *s : llvm::reverse(this->sgSections)) {
+    if (s->getAddr() != std::nullopt)
+      break;
+    s->outSecOff = off & ~1;
+    Defined(s->file, StringRef(), s->sym->binding, s->sym->stOther,
+            s->sym->type, (s->outSecOff - getVA()) | 1, this->entsize, this)
+        .overwrite(*s->sym);
+    off += s->entsize;
+  }
+}
+
+void ArmCmseSGVeneer::writeTo(uint8_t *buf) {
+  const uint8_t data[] = {
+      0x7f, 0xe9, 0x7f, 0xe9, // SG
+      0x00, 0xf0, 0x00, 0xb0, // B.W S
+  };
+  memcpy(buf, data, sizeof(data));
+  uint64_t s = acleSeSym->getVA();
+  uint64_t p = getVA() + 4;
+  target->relocateNoSym(buf + 4, R_ARM_THM_JUMP24, s - p - 4);
+}
+
+// Write the CMSE import library to disk.
+// The CMSE import library is a relocatable object with only a symbol table.
+// The symbols are copies of the (absolute) symbols of the secure gateways
+// in the executable output by this link.
+// See Arm® v8-M Security Extensions: Requirements on Development Tools
+// https://developer.arm.com/documentation/ecm0359818/latest
+template <typename ELFT> void elf::writeARMCmseImportLib() {
+  if (config->cmseOutputLib.empty())
+    return;
+
+  StringTableSection *shstrtab =
+      make<StringTableSection>(".shstrtab", /*dynamic=*/false);
+  StringTableSection *strtab =
+      make<StringTableSection>(".strtab", /*dynamic=*/false);
+  SymbolTableBaseSection *impSymTab = make<SymbolTableSection<ELFT>>(*strtab);
+
+  SmallVector<std::pair<OutputSection *, SyntheticSection *>, 0> osIsPairs;
+  osIsPairs.push_back(
+      std::make_pair(make<OutputSection>(impSymTab->name, 0, 0), impSymTab));
+  osIsPairs.push_back(
+      std::make_pair(make<OutputSection>(strtab->name, 0, 0), strtab));
+  osIsPairs.push_back(
+      std::make_pair(make<OutputSection>(shstrtab->name, 0, 0), shstrtab));
+
+  for (auto &[osec, isec] : osIsPairs) {
+    osec->recordSection(isec);
+    osec->finalizeInputSections();
+  }
+
+  // Copy the secure gateway entry symbols to the import library symbol table.
+  for (const auto &[_, sym] : symtab.cmseSymVector) {
+    Defined *d = cast<Defined>(sym);
+    impSymTab->addSymbol(makeDefined(nullptr, d->getName(), d->computeBinding(),
+                                     /*stOther=*/0, STT_FUNC, d->getVA(),
+                                     d->getSize(), nullptr));
+  }
+
+  // Assign section indices and record section names in .shstrtab
+  size_t idx = 0;
+  for (auto &[osec, _] : osIsPairs) {
+    osec->sectionIndex = ++idx;
+    osec->shName = shstrtab->addString(osec->name);
+  }
+
+  for (auto &[osec, isec] : osIsPairs) {
+    osec->size = isec->getSize();
+    isec->finalizeContents();
+  }
+
+  uint64_t off = sizeof(typename ELFT::Ehdr);
+  // Assign file offsets to output sections.
+  for (auto &[osec, _] : osIsPairs) {
+    osec->offset = alignToPowerOf2(off, osec->addralign);
+    off = osec->offset + osec->size;
+  }
+
+  uint64_t sectionHeaderOff = alignToPowerOf2(off, config->wordsize);
+  auto shnum = osIsPairs.size() + 1;
+  uint64_t fileSize = sectionHeaderOff + shnum * sizeof(typename ELFT::Shdr);
+
+  unlinkAsync(config->cmseOutputLib);
+  unsigned flags = 0;
+  if (!config->mmapOutputFile)
+    flags |= FileOutputBuffer::F_no_mmap;
+
+  Expected<std::unique_ptr<FileOutputBuffer>> bufferOrErr =
+      FileOutputBuffer::create(config->cmseOutputLib, fileSize, flags);
+
+  if (!bufferOrErr) {
+    error("failed to open " + config->cmseOutputLib + ": " +
+          llvm::toString(bufferOrErr.takeError()));
+    return;
+  }
+
+  // Write the ELF Header
+  std::unique_ptr<FileOutputBuffer> &buffer = *bufferOrErr;
+  uint8_t *buf = buffer->getBufferStart();
+  memcpy(buf, "\177ELF", 4);
+  auto *eHdr = reinterpret_cast<typename ELFT::Ehdr *>(buf);
+  eHdr->e_type = ET_REL;
+  eHdr->e_entry = 0;
+  eHdr->e_shoff = sectionHeaderOff;
+  eHdr->e_ident[EI_CLASS] = ELFCLASS32;
+  eHdr->e_ident[EI_DATA] = config->isLE ? ELFDATA2LSB : ELFDATA2MSB;
+  eHdr->e_ident[EI_VERSION] = EV_CURRENT;
+  eHdr->e_ident[EI_OSABI] = config->osabi;
+  eHdr->e_ident[EI_ABIVERSION] = 0;
+  eHdr->e_machine = EM_ARM;
+  eHdr->e_version = EV_CURRENT;
+  eHdr->e_flags = config->eflags;
+  eHdr->e_ehsize = sizeof(typename ELFT::Ehdr);
+  eHdr->e_phnum = 0;
+  eHdr->e_shentsize = sizeof(typename ELFT::Shdr);
+  eHdr->e_phoff = 0;
+  eHdr->e_phentsize = 0;
+  eHdr->e_shnum = shnum;
+  eHdr->e_shstrndx = shstrtab->getParent()->sectionIndex;
+
+  // Write the section header table.
+  auto *sHdrs = reinterpret_cast<typename ELFT::Shdr *>(buf + eHdr->e_shoff);
+  for (auto &[osec, _] : osIsPairs)
+    osec->writeHeaderTo<ELFT>(++sHdrs);
+
+  // Write section contents to a mmap'ed file.
+  {
+    parallel::TaskGroup tg;
+    for (auto &[osec, _] : osIsPairs)
+      osec->writeTo<ELFT>(buf + osec->offset, tg);
+  }
+
+  if (auto e = buffer->commit())
+    fatal("failed to write output '" + buffer->getPath() +
+          "': " + toString(std::move(e)));
+}
+
+template void elf::writeARMCmseImportLib<ELF32LE>();
+template void elf::writeARMCmseImportLib<ELF32BE>();
+template void elf::writeARMCmseImportLib<ELF64LE>();
+template void elf::writeARMCmseImportLib<ELF64BE>();
+
+template void ObjFile<ELF32LE>::importCmseSymbols();
+template void ObjFile<ELF32BE>::importCmseSymbols();
+template void ObjFile<ELF64LE>::importCmseSymbols();
+template void ObjFile<ELF64BE>::importCmseSymbols();
+
 TargetInfo *elf::getARMTargetInfo() {
   static ARM target;
   return &target;
diff --git a/lld/ELF/Config.h b/lld/ELF/Config.h
--- a/lld/ELF/Config.h
+++ b/lld/ELF/Config.h
@@ -122,6 +122,7 @@
 
   std::unique_ptr<BitcodeCompiler> lto;
   std::vector<InputFile *> files;
+  std::vector<InputFile *> armCmseImpLib;
 
 public:
   SmallVector<std::pair<StringRef, unsigned>, 0> archiveFiles;
@@ -166,6 +167,8 @@
   llvm::StringRef thinLTOCacheDir;
   llvm::StringRef thinLTOIndexOnlyArg;
   llvm::StringRef whyExtract;
+  llvm::StringRef cmseInputLib;
+  llvm::StringRef cmseOutputLib;
   StringRef zBtiReport = "none";
   StringRef zCetReport = "none";
   llvm::StringRef ltoBasicBlockSections;
@@ -186,11 +189,13 @@
   llvm::MapVector<std::pair<const InputSectionBase *, const InputSectionBase *>,
                   uint64_t>
       callGraphProfile;
+  bool cmseImplib = false;
   bool allowMultipleDefinition;
   bool androidPackDynRelocs = false;
   bool armHasBlx = false;
   bool armHasMovtMovw = false;
   bool armJ1J2BranchEncoding = false;
+  bool armCMSESupport = false;
   bool asNeeded = false;
   BsymbolicKind bsymbolic = BsymbolicKind::None;
   bool callGraphProfileSort;
diff --git a/lld/ELF/Driver.cpp b/lld/ELF/Driver.cpp
--- a/lld/ELF/Driver.cpp
+++ b/lld/ELF/Driver.cpp
@@ -340,6 +340,15 @@
   if (config->emachine == EM_MIPS && config->gnuHash)
     error("the .gnu.hash section is not compatible with the MIPS target");
 
+  if (config->emachine != EM_ARM) {
+    if (config->cmseImplib)
+      error("--cmse-implib is only supported on ARM targets");
+    if (!config->cmseInputLib.empty())
+      error("--in-implib is only supported on ARM targets");
+    if (!config->cmseOutputLib.empty())
+      error("--out-implib is only supported on ARM targets");
+  }
+
   if (config->fixCortexA53Errata843419 && config->emachine != EM_AARCH64)
     error("--fix-cortex-a53-843419 is only supported on AArch64 targets");
 
@@ -1114,6 +1123,9 @@
   config->fini = args.getLastArgValue(OPT_fini, "_fini");
   config->fixCortexA53Errata843419 = args.hasArg(OPT_fix_cortex_a53_843419) &&
                                      !args.hasArg(OPT_relocatable);
+  config->cmseImplib = args.hasArg(OPT_cmse_implib);
+  config->cmseInputLib = args.getLastArgValue(OPT_in_implib);
+  config->cmseOutputLib = args.getLastArgValue(OPT_out_implib);
   config->fixCortexA8 =
       args.hasArg(OPT_fix_cortex_a8) && !args.hasArg(OPT_relocatable);
   config->fortranCommon =
@@ -1663,6 +1675,12 @@
         files.back()->justSymbols = true;
       }
       break;
+    case OPT_in_implib:
+      if (!armCmseImpLib.empty())
+        error("multiple CMSE import libraries not supported");
+      else if (std::optional<MemoryBufferRef> mb = readFile(arg->getValue()))
+        armCmseImpLib.push_back(createObjFile(*mb));
+      break;
     case OPT_start_group:
       if (InputFile::isInGroup)
         error("nested --start-group");
@@ -2539,9 +2557,14 @@
   {
     llvm::TimeTraceScope timeScope("Parse input files");
     for (size_t i = 0; i < files.size(); ++i) {
-      llvm::TimeTraceScope timeScope("Parse input files", files[i]->getName());
+      llvm::TimeTraceScope timeScope("Parse input file", files[i]->getName());
       parseFile(files[i]);
     }
+    if (!armCmseImpLib.empty()) {
+      llvm::TimeTraceScope timeScope("Parse Arm CMSE input lib",
+                                     armCmseImpLib[0]->getName());
+      parseArmCMSEImportLib(armCmseImpLib[0]);
+    }
   }
 
   // Now that we have every file, we can decide if we will need a
@@ -2706,6 +2729,9 @@
   if (args.hasArg(OPT_exclude_libs))
     excludeLibs(args);
 
+  // Process CMSE symbols
+  processArmCmseSymbol();
+
   // Apply symbol renames for --wrap and combine foo@v1 and foo@@v1.
   redirectSymbols(wrapped);
 
diff --git a/lld/ELF/InputFiles.h b/lld/ELF/InputFiles.h
--- a/lld/ELF/InputFiles.h
+++ b/lld/ELF/InputFiles.h
@@ -48,6 +48,9 @@
 // Add symbols in File to the symbol table.
 void parseFile(InputFile *file);
 
+// Add symbols in File to the symbol table.
+void parseArmCMSEImportLib(InputFile *file);
+
 // The root class of input files.
 class InputFile {
 protected:
@@ -281,6 +284,7 @@
 
   void initSectionsAndLocalSyms(bool ignoreComdats);
   void postParse();
+  void importCmseSymbols();
 
 private:
   void initializeSections(bool ignoreComdats,
diff --git a/lld/ELF/InputFiles.cpp b/lld/ELF/InputFiles.cpp
--- a/lld/ELF/InputFiles.cpp
+++ b/lld/ELF/InputFiles.cpp
@@ -177,6 +177,10 @@
       config->armHasMovtMovw = true;
     break;
   }
+
+  // Only ARMv8-M or later architectures have CMSE support.
+  if (arch >= ARMBuildAttrs::CPUArch::v8_M_Base)
+    config->armCMSESupport = true;
 }
 
 InputFile::InputFile(Kind k, MemoryBufferRef m)
@@ -294,6 +298,14 @@
 // Add symbols in File to the symbol table.
 void elf::parseFile(InputFile *file) { invokeELFT(doParseFile, file); }
 
+template <class ELFT> static void doParseArmCMSEImportLib(InputFile *file) {
+  cast<ObjFile<ELFT>>(file)->importCmseSymbols();
+}
+
+void elf::parseArmCMSEImportLib(InputFile *file) {
+  invokeELFT(doParseArmCMSEImportLib, file);
+}
+
 // Concatenates arguments to construct a string representing an error location.
 static std::string createFileLineMsg(StringRef path, unsigned line) {
   std::string filename = std::string(path::filename(path));
@@ -1120,6 +1132,7 @@
 template <class ELFT> void ObjFile<ELFT>::postParse() {
   static std::mutex mu;
   ArrayRef<Elf_Sym> eSyms = this->getELFSyms<ELFT>();
+
   for (size_t i = firstGlobal, end = eSyms.size(); i != end; ++i) {
     const Elf_Sym &eSym = eSyms[i];
     Symbol &sym = *symbols[i];
diff --git a/lld/ELF/LinkerScript.h b/lld/ELF/LinkerScript.h
--- a/lld/ELF/LinkerScript.h
+++ b/lld/ELF/LinkerScript.h
@@ -315,6 +315,7 @@
 
   void addOrphanSections();
   void diagnoseOrphanHandling() const;
+  void diagnoseMissingSGSectionAddress() const;
   void adjustOutputSections();
   void adjustSectionsAfterSorting();
 
diff --git a/lld/ELF/LinkerScript.cpp b/lld/ELF/LinkerScript.cpp
--- a/lld/ELF/LinkerScript.cpp
+++ b/lld/ELF/LinkerScript.cpp
@@ -900,6 +900,42 @@
   }
 }
 
+void LinkerScript::diagnoseMissingSGSectionAddress() const {
+  if (!config->cmseImplib)
+    return;
+
+  bool sgStubsFound = false;
+  for (InputSectionBase *isec : ctx.inputSections) {
+    if (getOutputSectionName(isec) == ".gnu.sgstubs") {
+      sgStubsFound = true;
+      break;
+    }
+  }
+  if (!sgStubsFound)
+    return;
+
+  auto inLinkerScript = [&]() {
+    // Nothing to clash if there are no section commands.
+    if (!hasSectionsCommand)
+      return false;
+    // Cannot clash if .gnu.sgstubs is an orphan section.
+    for (const InputSectionBase *isec : orphanSections)
+      if (getOutputSectionName(isec) == ".gnu.sgstubs")
+        return false;
+    return true;
+  };
+
+  // --section-start .gnu.sgstubs=<addr> specified via command line
+  auto inCmdLine = config->sectionStartMap.find(".gnu.sgstubs") !=
+                   config->sectionStartMap.end();
+  auto linkerscript = inLinkerScript();
+  if (inCmdLine && linkerscript)
+    warn("addresses assigned to the veneers output section .gnu.sgstubs via "
+         "--section-start and linker script may potentially clash");
+  if (!inCmdLine && !linkerscript)
+    error("no address assigned to the veneers output section .gnu.sgstubs");
+}
+
 // This function searches for a memory region to place the given output
 // section in. If found, a pointer to the appropriate memory region is
 // returned in the first member of the pair. Otherwise, a nullptr is returned.
diff --git a/lld/ELF/Options.td b/lld/ELF/Options.td
--- a/lld/ELF/Options.td
+++ b/lld/ELF/Options.td
@@ -80,6 +80,19 @@
 
 def O: JoinedOrSeparate<["-"], "O">, HelpText<"Optimize output file size">;
 
+def cmse_implib: FF<"cmse-implib">,
+  HelpText<"Make the output library to be a CMSE secure code import library">;
+
+defm in_implib: EEq<"in-implib",
+    "Read an existing CMSE secure code import library and preserve entry function addresses in the "
+    "resulting new CMSE secure code import library (optional when creating a CMSE secure image)">,
+  MetaVarName<"<file>">;
+
+defm out_implib: EEq<"out-implib",
+    "Output the CMSE secure code import library to the location specified (required when creating "
+    "a CMSE secure image)">,
+  MetaVarName<"<file>">;
+
 defm Tbss: Eq<"Tbss", "Same as --section-start with .bss as the sectionname">;
 
 defm Tdata: Eq<"Tdata", "Same as --section-start with .data as the sectionname">;
diff --git a/lld/ELF/SymbolTable.h b/lld/ELF/SymbolTable.h
--- a/lld/ELF/SymbolTable.h
+++ b/lld/ELF/SymbolTable.h
@@ -60,6 +60,13 @@
   // is used to uniquify them.
   llvm::DenseMap<llvm::CachedHashStringRef, const InputFile *> comdatGroups;
 
+  void addCmseSymPair(Symbol *acleSeSym, Symbol *sym);
+  // The list of __acle_se_<sym>, <sym> pairs found in the input objects.
+  SmallVector<std::pair<Symbol *, Symbol *>, 0> cmseSymVector;
+  // Map of symbols defined in the CMSE import library. The linker must preserve
+  // the addresses in the output objects.
+  llvm::StringMap<Defined *> cmseImportLib;
+
 private:
   SmallVector<Symbol *, 0> findByVersion(SymbolVersion ver);
   SmallVector<Symbol *, 0> findAllByVersion(SymbolVersion ver,
diff --git a/lld/ELF/SymbolTable.cpp b/lld/ELF/SymbolTable.cpp
--- a/lld/ELF/SymbolTable.cpp
+++ b/lld/ELF/SymbolTable.cpp
@@ -99,6 +99,10 @@
   return sym;
 }
 
+void SymbolTable::addCmseSymPair(Symbol *acleSeSym, Symbol *sym) {
+  cmseSymVector.push_back(std::make_pair(acleSeSym, sym));
+}
+
 // This variant of addSymbol is used by BinaryFile::parse to check duplicate
 // symbol errors.
 Symbol *SymbolTable::addAndCheckDuplicate(const Defined &newSym) {
diff --git a/lld/ELF/SyntheticSections.h b/lld/ELF/SyntheticSections.h
--- a/lld/ELF/SyntheticSections.h
+++ b/lld/ELF/SyntheticSections.h
@@ -1143,6 +1143,51 @@
   size_t size = 0;
 };
 
+// Cortex-M Security Extensions. Prefix for functions that should be exported
+// for the non-secure world.
+const char ACLESESYM_PREFIX[] = "__acle_se_";
+const int ACLESESYM_SIZE = 8;
+class ArmCmseSGVeneer : public SyntheticSection {
+public:
+  ArmCmseSGVeneer(Symbol *sym, Symbol *acleSeSym,
+                  std::optional<uint64_t> addr = std::nullopt)
+      : SyntheticSection(llvm::ELF::SHF_ALLOC | llvm::ELF::SHF_EXECINSTR,
+                         llvm::ELF::SHT_PROGBITS,
+                         /*alignment=*/32, ".gnu.sgstubs"),
+        sym(sym), acleSeSym(acleSeSym), entAddr{addr} {
+    entsize = ACLESESYM_SIZE;
+  }
+
+  void writeTo(uint8_t *buf) override;
+  size_t getSize() const override { return this->entsize; };
+  const std::optional<uint64_t> getAddr() const { return this->entAddr; };
+
+  Symbol *sym;
+  Symbol *acleSeSym;
+
+private:
+  const std::optional<uint64_t> entAddr;
+};
+
+class ArmCmseSGSection : public SyntheticSection {
+public:
+  ArmCmseSGSection();
+  bool isNeeded() const override { return !entries.empty(); }
+  size_t getSize() const override;
+  void writeTo(uint8_t *buf) override;
+  void addSGVeneer(Symbol *sym, Symbol *ext_sym);
+  inline void addMappingSymbol();
+  void finalizeContents() override;
+  void exportEntries(SymbolTableBaseSection *symTab);
+  uint64_t impLibMinAddr = -1;
+  uint64_t impLibMaxAddr = 0;
+
+private:
+  SmallVector<std::pair<Symbol *, Symbol *>, 0> entries;
+  SmallVector<ArmCmseSGVeneer *, 0> sgSections;
+  uint64_t newEntries = 0;
+};
+
 // Used to compute outSecOff of .got2 in each object file. This is needed to
 // synthesize PLT entries for PPC32 Secure PLT ABI.
 class PPC32Got2Section final : public SyntheticSection {
@@ -1279,6 +1324,7 @@
   std::unique_ptr<GotSection> got;
   std::unique_ptr<GotPltSection> gotPlt;
   std::unique_ptr<IgotPltSection> igotPlt;
+  std::unique_ptr<SyntheticSection> armCmseSGSection;
   std::unique_ptr<PPC64LongBranchTargetSection> ppc64LongBranchTarget;
   std::unique_ptr<SyntheticSection> mipsAbiFlags;
   std::unique_ptr<MipsGotSection> mipsGot;
diff --git a/lld/ELF/SyntheticSections.cpp b/lld/ELF/SyntheticSections.cpp
--- a/lld/ELF/SyntheticSections.cpp
+++ b/lld/ELF/SyntheticSections.cpp
@@ -3831,6 +3831,7 @@
   strTab.reset();
   symTab.reset();
   symTabShndx.reset();
+  armCmseSGSection.reset();
 }
 
 constexpr char kMemtagAndroidNoteName[] = "Android";
diff --git a/lld/ELF/Target.h b/lld/ELF/Target.h
--- a/lld/ELF/Target.h
+++ b/lld/ELF/Target.h
@@ -194,6 +194,8 @@
   return getErrorPlace(loc).loc;
 }
 
+void processArmCmseSymbol();
+
 void writePPC32GlinkSection(uint8_t *buf, size_t numEntries);
 
 unsigned getPPCDFormOp(unsigned secondaryOp);
@@ -215,6 +217,7 @@
 void addPPC64SaveRestore();
 uint64_t getPPC64TocBase();
 uint64_t getAArch64Page(uint64_t expr);
+template <typename ELFT> void writeARMCmseImportLib();
 void riscvFinalizeRelax(int passes);
 void mergeRISCVAttributesSections();
 
diff --git a/lld/ELF/Writer.cpp b/lld/ELF/Writer.cpp
--- a/lld/ELF/Writer.cpp
+++ b/lld/ELF/Writer.cpp
@@ -453,6 +453,9 @@
   in.igotPlt = std::make_unique<IgotPltSection>();
   add(*in.igotPlt);
 
+  in.armCmseSGSection = std::make_unique<ArmCmseSGSection>();
+  add(*in.armCmseSGSection);
+
   // _GLOBAL_OFFSET_TABLE_ is defined relative to either .got.plt or .got. Treat
   // it as a relocation and ensure the referenced section is created.
   if (ElfSym::globalOffsetTable && config->emachine != EM_MIPS) {
@@ -590,6 +593,9 @@
     if (auto e = buffer->commit())
       fatal("failed to write output '" + buffer->getPath() +
             "': " + toString(std::move(e)));
+
+    if (config->emachine == EM_ARM)
+      writeARMCmseImportLib<ELFT>();
   }
 }
 
@@ -1985,6 +1991,7 @@
 
   removeUnusedSyntheticSections();
   script->diagnoseOrphanHandling();
+  script->diagnoseMissingSGSectionAddress();
 
   sortSections();
 
@@ -2133,6 +2140,7 @@
     // static symbol table.
     finalizeSynthetic(in.symTab.get());
     finalizeSynthetic(in.ppc64LongBranchTarget.get());
+    finalizeSynthetic(in.armCmseSGSection.get());
   }
 
   // Relaxation to delete inter-basic block jumps created by basic block
diff --git a/lld/test/ELF/Inputs/arm-cmse-macros.s b/lld/test/ELF/Inputs/arm-cmse-macros.s
new file mode 100644
--- /dev/null
+++ b/lld/test/ELF/Inputs/arm-cmse-macros.s
@@ -0,0 +1,32 @@
+/// Because the addresses of __acle_se_\sym_name and \sym_name are equal,
+/// the linker creates a secure gateway in ".gnu.sgstubs".
+.macro cmse_veneer sym_name, sym_type, sym_binding, acle_sym_type, acle_sym_binding
+.align  2
+.\sym_binding  \sym_name
+.\acle_sym_binding  __acle_se_\sym_name
+.type  \sym_name, %\sym_type
+.type  __acle_se_\sym_name, %\acle_sym_type
+\sym_name:
+__acle_se_\sym_name:
+  nop
+.size  \sym_name, .-\sym_name
+.size  __acle_se_\sym_name, .-__acle_se_\sym_name
+.endm
+
+/// Because the addresses of __acle_se_\sym_name and \sym_name are not equal,
+/// the linker considers that an inline secure gateway exists and does not
+/// create one.
+.macro cmse_no_veneer sym_name, sym_type, sym_binding, acle_sym_type, acle_sym_binding
+.align  2
+.\sym_binding  \sym_name
+.\acle_sym_binding  __acle_se_\sym_name
+.type  \sym_name, %\sym_type
+.type  __acle_se_\sym_name, %\acle_sym_type
+\sym_name:
+	sg
+  nop
+__acle_se_\sym_name:
+  nop
+.size  \sym_name, .-\sym_name
+.size  __acle_se_\sym_name, .-__acle_se_\sym_name
+.endm
diff --git a/lld/test/ELF/aarch64-cmse.s b/lld/test/ELF/aarch64-cmse.s
new file mode 100644
--- /dev/null
+++ b/lld/test/ELF/aarch64-cmse.s
@@ -0,0 +1,16 @@
+# REQUIRES: aarch64
+# RUN: yaml2obj %s -o %t.o
+# RUN: not ld.lld --cmse-implib %t.o -o /dev/null 2>&1 | FileCheck %s --check-prefix=ERR_CMSE_IMPLIB
+# RUN: not ld.lld --in-implib=%t.o %t.o -o /dev/null 2>&1 | FileCheck %s --check-prefix=ERR_IN_IMPLIB
+# RUN: not ld.lld --out-implib=out.lib %t.o -o /dev/null 2>&1 | FileCheck %s --check-prefix=ERR_OUT_IMPLIB
+
+# ERR_CMSE_IMPLIB: error: --cmse-implib is only supported on ARM targets
+# ERR_IN_IMPLIB: error: --in-implib is only supported on ARM targets
+# ERR_OUT_IMPLIB: error: --out-implib is only supported on ARM targets
+
+!ELF
+FileHeader:
+  Class:           ELFCLASS64
+  Data:            ELFDATA2LSB
+  Type:            ET_REL
+  Machine:         EM_AARCH64
diff --git a/lld/test/ELF/arm-cmse-check-startaddress.s b/lld/test/ELF/arm-cmse-check-startaddress.s
new file mode 100644
--- /dev/null
+++ b/lld/test/ELF/arm-cmse-check-startaddress.s
@@ -0,0 +1,45 @@
+/// Test that the address of .gnu.sgstubs can be specified via command line or linker script.
+/// Test that the linker warns when the address of .gnu.sgstubs is specified via both command line and linker script.
+/// Test that the linker errors when the address of .gnu.sgstubs is not specified using either method.
+
+// REQUIRES: arm
+// RUN: split-file %s %t
+
+// RUN: llvm-mc -arm-add-build-attributes --triple=thumbv8m.main -filetype=obj -I%S/Inputs/ %t/asm -o %t.o
+// RUN: ld.lld --cmse-implib -Ttext=0x8000 --section-start .gnu.sgstubs=0x20000 --script %t/with_sgstubs.script %t.o -o %t1 2>&1 | FileCheck %s --check-prefix=WARN
+// RUN: ld.lld --cmse-implib -Ttext=0x8000 --section-start .gnu.sgstubs=0x20000 --script %t/wout_sgstubs.script %t.o -o %t2 2>&1 | FileCheck %s --check-prefixes=NOWARN,NOERROR
+// RUN: ld.lld --cmse-implib -Ttext=0x8000 --section-start .gnu.sgstubs=0x20000 %t.o -o %t3 2>&1 | FileCheck %s --check-prefixes=NOWARN,NOERROR
+// RUN: ld.lld --cmse-implib -Ttext=0x8000 --script %t/with_sgstubs.script %t.o -o %t4 2>&1 | FileCheck %s --check-prefixes=NOWARN,NOERROR
+// RUN: not ld.lld --cmse-implib -Ttext=0x8000 --script %t/wout_sgstubs.script %t.o -o %t5 2>&1 | FileCheck %s --check-prefix=ERROR
+
+// RUN: llvm-readelf -S %t1 | FileCheck %s --check-prefix=ADDRCMDLINE
+// RUN: llvm-readelf -S %t2 | FileCheck %s --check-prefix=ADDRCMDLINE
+// RUN: llvm-readelf -S %t3 | FileCheck %s --check-prefix=ADDRCMDLINE
+// RUN: llvm-readelf -S %t4 | FileCheck %s --check-prefix=ADDRLNKSCRIPT
+
+// WARN: warning: addresses assigned to the veneers output section .gnu.sgstubs via --section-start and linker script may potentially clash
+// NOWARN-NOT: warning: addresses assigned to the veneers output section .gnu.sgstubs via --section-start and linker script may potentially clash
+
+// ERROR: error: no address assigned to the veneers output section .gnu.sgstubs
+// NOERROR-NOT: error:
+
+///                       Name          Type         Address    Off   Size ES Flg Lk Inf Al
+// ADDRCMDLINE:   .gnu.sgstubs      PROGBITS        00020000 020000 000008 08  AX  0   0 32
+// ADDRLNKSCRIPT: .gnu.sgstubs      PROGBITS        00040000 040000 000008 08  AX  0   0 32
+
+//--- asm
+.include "arm-cmse-macros.s"
+
+  .align  2
+cmse_veneer foo, function, global, function, global
+
+//--- with_sgstubs.script
+SECTIONS {
+  .text : { *(.text) }
+  .gnu.sgstubs 0x40000 : { *(.gnu.sgstubs*) }
+}
+
+//--- wout_sgstubs.script
+SECTIONS {
+  .text : { *(.text) }
+}
diff --git a/lld/test/ELF/arm-cmse-check-sym-attrs.s b/lld/test/ELF/arm-cmse-check-sym-attrs.s
new file mode 100644
--- /dev/null
+++ b/lld/test/ELF/arm-cmse-check-sym-attrs.s
@@ -0,0 +1,101 @@
+// REQUIRES: arm
+// RUN: llvm-mc -arm-add-build-attributes -filetype=obj -I %S/Inputs --triple=armv9a %s -o %t1.o
+// RUN: not ld.lld --cmse-implib %t1.o -o /dev/null 2>&1 | FileCheck %s --check-prefix ERROR
+
+.include "arm-cmse-macros.s"
+
+  .text
+  .thumb
+
+/// Valid sequences
+/// both sym and __acle_se_sym should be global or weak Thumb code symbols.
+  cmse_veneer valid_1, function, global, function, global
+  cmse_veneer valid_2, function,   weak, function,   weak
+  cmse_veneer valid_3, function,   weak, function, global
+  cmse_veneer valid_4, function, global, function,   weak
+
+/// Invalid sequences
+/// __acle_se_sym is an object
+  cmse_veneer invalid_1, function, global,   object, global
+  cmse_veneer invalid_2, function, global,   object,   weak
+/// sym is an object
+  cmse_veneer invalid_3,   object, global, function, global
+  cmse_veneer invalid_4,   object, global, function,   weak
+/// sym is local
+  cmse_veneer invalid_5, function,  local, function, global
+  cmse_veneer invalid_6, function,  local, function,   weak
+
+/// __acle_se_invalid_7 not defined.
+  .global invalid_7
+	.type	invalid_7, %function
+  .global __acle_se_invalid_7
+  .thumb_func
+invalid_7:
+
+/// invalid_8 not defined.
+  .global __acle_se_invalid_8
+  .thumb_func
+__acle_se_invalid_8:
+
+// Absolute symbols with same values
+  .global invalid_9
+  .global __acle_se_invalid_9
+	.type	__acle_se_invalid_9, %function
+	.type	invalid_9, %function
+__acle_se_invalid_9=0x1001
+invalid_9=0x1001
+	.size	invalid_9, 0
+  .size __acle_se_invalid_9, 0
+
+// Absolute symbols with different values
+	.align 2
+	.global	__acle_se_invalid_10
+	.global	invalid_10
+	.type	__acle_se_invalid_10, %function
+	.type	invalid_10, %function
+__acle_se_invalid_10 = 0x10001
+invalid_10 = 0x10005
+	.size	invalid_10, 0
+  .size __acle_se_invalid_10, 0
+
+  .section nonthumb
+  .thumb
+  .align  2
+  .global  invalid_11
+  .global  __acle_se_invalid_11
+  .type  invalid_11, %function
+  .type  __acle_se_invalid_11, %function
+invalid_11:
+  .arm
+/// Invalid non-thumb function symbol __acle_se_invalid_11
+__acle_se_invalid_11:
+  .size  invalid_11, .-invalid_11
+  .size  __acle_se_invalid_11, .-__acle_se_invalid_11
+
+  .global  invalid_12
+  .global  __acle_se_invalid_12
+  .type  invalid_12, %function
+  .type  __acle_se_invalid_12, %function
+/// Invalid non-thumb function symbol invalid_12
+invalid_12:
+  .thumb
+__acle_se_invalid_12:
+  .size  invalid_12, .-invalid_12
+  .size  __acle_se_invalid_12, .-__acle_se_invalid_12
+
+// ERROR-NOT: __acle_se_valid_1
+// ERROR-NOT: __acle_se_valid_2
+// ERROR-NOT: __acle_se_valid_3
+// ERROR-NOT: __acle_se_valid_4
+// ERROR: error: {{.*}}: cmse special symbol '__acle_se_invalid_1'; is not a Thumb function definition
+// ERROR: error: {{.*}}: cmse special symbol '__acle_se_invalid_2'; is not a Thumb function definition
+// ERROR: error: {{.*}}: cmse entry function 'invalid_3'; is not a Thumb function definition
+// ERROR: error: {{.*}}: cmse entry function 'invalid_4'; is not a Thumb function definition
+// ERROR: error: {{.*}}: cmse special symbol '__acle_se_invalid_5' detected, but no associated entry function definition 'invalid_5' with external linkage found
+// ERROR: error: {{.*}}: cmse special symbol '__acle_se_invalid_6' detected, but no associated entry function definition 'invalid_6' with external linkage found
+// ERROR: error: {{.*}}: cmse special symbol '__acle_se_invalid_7' is not defined
+// ERROR: error: {{.*}}: cmse special symbol '__acle_se_invalid_8' detected, but no associated entry function definition 'invalid_8' with external linkage found
+// ERROR: error: {{.*}}: cmse special symbol '__acle_se_invalid_9'; cannot be an absolute symbol
+// ERROR: error: {{.*}}: cmse special symbol '__acle_se_invalid_10'; cannot be an absolute symbol
+// ERROR: error: {{.*}}: cmse special symbol '__acle_se_invalid_11'; is not a Thumb function definition
+// ERROR: error: {{.*}}: cmse entry function 'invalid_12'; is not a Thumb function definition
diff --git a/lld/test/ELF/arm-cmse-implib-error.s b/lld/test/ELF/arm-cmse-implib-error.s
new file mode 100644
--- /dev/null
+++ b/lld/test/ELF/arm-cmse-implib-error.s
@@ -0,0 +1,73 @@
+// REQUIRES: arm
+// RUN: split-file %s %t
+// RUN: llvm-mc -arm-add-build-attributes -filetype=obj --triple=thumbv8m.base %t/lib -o %t.lib
+// RUN: llvm-mc -arm-add-build-attributes -filetype=obj --triple=thumbv8m.base %t/app -o %tapp.o
+// RUN: llvm-objcopy --redefine-sym=entry7_duplicate=entry6_duplicate %t.lib
+// RUN: not ld.lld --cmse-implib --in-implib=%t.lib %tapp.o -o /dev/null 2>&1 | FileCheck %s
+// RUN: not ld.lld --cmse-implib --in-implib=%t.lib --in-implib=%t.lib %tapp.o -o /dev/null 2>&1 | FileCheck %s --check-prefix=MULT_INIMPLIB_ERR
+
+//--- app
+  .align  2
+  .global entry
+  .thumb
+  .thumb_func
+  .type  entry, %function
+entry:
+  bx lr
+  .size  entry, .-entry
+
+//--- lib
+    .text
+    .thumb
+
+    /// Symbol not absolute.
+    .global entry1_not_absolute
+    .type entry1_not_absolute, STT_FUNC
+    .thumb_func
+entry1_not_absolute:
+    .size entry1_not_absolute, 8
+
+    /// Symbol not global or weak.
+    .local entry2_not_external
+    .type entry2_not_external, STT_FUNC
+entry2_not_external=0x1001
+    .size entry2_not_external, 8
+
+    /// Symbol not the function type.
+    .global entry3_not_function
+    .type entry3_not_function, STT_NOTYPE
+entry3_not_function=0x1001
+    .size entry3_not_function, 8
+
+    /// Symbol not a Thumb code symbol.
+    .global entry4_not_thumb
+    .type entry4_not_thumb, STT_FUNC
+entry4_not_thumb=0x1000
+    .size entry4_not_thumb, 8
+
+    /// Symbol with incorrect size.
+    .global entry5_incorrect_size
+    .type entry5_incorrect_size, STT_FUNC
+entry5_incorrect_size=0x1009
+    .size entry5_incorrect_size, 6
+
+    /// Duplicate symbols.
+    .global entry6_duplicate
+    .type entry6_duplicate, STT_FUNC
+entry6_duplicate=0x1001
+    .size entry6_duplicate, 8
+
+    /// entry7_duplicate gets renamed to entry6_duplicate by llvm-objcopy.
+    .global entry7_duplicate
+    .type entry7_duplicate, STT_FUNC
+entry7_duplicate=0x1009
+    .size entry7_duplicate, 8
+
+// CHECK: error: CMSE symbol entry2_not_external in import library {{.*}} is not global
+// CHECK: error: CMSE symbol entry1_not_absolute in import library {{.*}} is not absolute
+// CHECK: error: CMSE symbol entry3_not_function in import library {{.*}} is not of function type
+// CHECK: error: CMSE symbol entry4_not_thumb in import library {{.*}} is not a Thumb code symbol
+// CHECK: warning: CMSE symbol entry5_incorrect_size in import library {{.*}} does not have correct size of 8 bytes
+// CHECK: error: CMSE symbol entry6_duplicate is multiply defined in import library {{.*}}
+
+// MULT_INIMPLIB_ERR: error: multiple CMSE import libraries not supported
diff --git a/lld/test/ELF/arm-cmse-implib-startaddress-mismatch.s b/lld/test/ELF/arm-cmse-implib-startaddress-mismatch.s
new file mode 100644
--- /dev/null
+++ b/lld/test/ELF/arm-cmse-implib-startaddress-mismatch.s
@@ -0,0 +1,20 @@
+/// Test that the linker diagnoses cases where the linker synthesized veneer addresses
+/// specified by the CMSE input library cannot be placed at the .gnu.sgstubs section address.
+
+// REQUIRES: arm
+// RUN: llvm-mc -arm-add-build-attributes -filetype=obj --triple=thumbv8m.main %s -I %S/Inputs -o %t.o
+/// Create a CMSE import library with a secure gateway veneer at 0x10000
+// RUN: ld.lld --cmse-implib --section-start .gnu.sgstubs=0x10000 %t.o -o %t --out-implib=%t.lib 2>&1 | FileCheck %s --check-prefix=NOERROR
+/// Create a new import library with the secure gateway veneer and .gnu.sgstubs specified at the same address
+// RUN: ld.lld --cmse-implib --section-start .gnu.sgstubs=0x10000 %t.o -o %t2 --out-implib=%t2.lib --in-implib=%t.lib 2>&1 | FileCheck %s --check-prefix=NOERROR
+/// Create a new import library with the secure gateway veneer specified at a same address but .gnu.sgstubs at a higher address.
+// RUN: not ld.lld --cmse-implib --section-start .gnu.sgstubs=0x11000 %t.o -o %t3 --out-implib=%t3.lib --in-implib=%t.lib 2>&1 | FileCheck %s --check-prefix=ERROR
+/// Create a new import library with the secure gateway veneer specified at a same address but .gnu.sgstubs at a lower address.
+// RUN: not ld.lld --cmse-implib --section-start .gnu.sgstubs=0x9000 %t.o -o %t4 --out-implib=%t4.lib --in-implib=%t.lib 2>&1 | FileCheck %s --check-prefix=ERROR
+
+ .include "arm-cmse-macros.s"
+
+  cmse_veneer entry, function, global, function, global
+
+// NOERROR-NOT: error:
+// ERROR: error: start address of '.gnu.sgstubs' is different from previous link
diff --git a/lld/test/ELF/arm-cmse-implib.s b/lld/test/ELF/arm-cmse-implib.s
new file mode 100644
--- /dev/null
+++ b/lld/test/ELF/arm-cmse-implib.s
@@ -0,0 +1,110 @@
+/// Test that addresses of secure gateways in an old import library are maintained in new import libraries.
+
+// REQUIRES: arm
+// RUN: split-file %s %t
+// RUN: llvm-mc -arm-add-build-attributes -filetype=obj --triple=thumbv8m.base %t/app -o %tapp.o
+// RUN: llvm-mc -arm-add-build-attributes -filetype=obj --triple=thumbv8m.base %t/implib-v1 -I %S/Inputs -o %t1.o
+// RUN: llvm-mc -arm-add-build-attributes -filetype=obj --triple=thumbv8m.base %t/implib-v2 -I %S/Inputs -o %t2.o
+
+// RUN: ld.lld -Ttext=0x8000 --section-start .gnu.sgstubs=0x20000 -o %t1 %tapp.o --out-implib=%t1.lib --cmse-implib %t1.o
+// RUN: llvm-readelf -s %t1 %t1.lib | FileCheck %s --check-prefix=CHECK1
+
+// RUN: ld.lld -Ttext=0x8000 --section-start .gnu.sgstubs=0x20000 -o %t2 %tapp.o --out-implib=%t2.lib --in-implib=%t1.lib --cmse-implib %t2.o
+// RUN: llvm-readelf -s %t2 %t2.lib | FileCheck %s --check-prefix=CHECK2
+
+//--- app
+
+	.align	2
+	.global	secure_entry
+	.type	secure_entry, %function
+secure_entry:
+	nop
+	.size	secure_entry, .-secure_entry
+
+//--- implib-v1
+
+    .include "arm-cmse-macros.s"
+
+    .syntax unified
+    .text
+
+  cmse_veneer foo, function, global, function, global
+  cmse_veneer bar, function, weak, function, global
+  cmse_no_veneer no_veneer1, function, weak, function, global
+  cmse_no_veneer no_veneer2, function, weak, function, weak
+
+//--- implib-v2
+
+    .include "arm-cmse-macros.s"
+
+    .syntax unified
+    .text
+
+  cmse_veneer baz, function, weak, function, global
+  cmse_veneer foo, function, global, function, global
+  cmse_veneer qux, function, global, function, global
+  cmse_no_veneer no_veneer1, function, weak, function, global
+  cmse_no_veneer no_veneer2, function, weak, function, weak
+
+/// Executable 1
+// CHECK1:      File:
+// CHECK1:      Symbol table '.symtab' contains 13 entries:
+// CHECK1-NEXT:    Num:    Value  Size Type    Bind   Vis       Ndx Name
+// CHECK1-NEXT:      0: 00000000     0 NOTYPE  LOCAL  DEFAULT   UND
+// CHECK1-NEXT:      1: 00020000     0 NOTYPE  LOCAL  DEFAULT     2 $t
+// CHECK1-NEXT:      2: 00008000     0 NOTYPE  LOCAL  DEFAULT     1 $t.0
+// CHECK1-NEXT:      3: 00008004     0 NOTYPE  LOCAL  DEFAULT     1 $t.0
+// CHECK1-NEXT:      4: 00008001     2 FUNC    GLOBAL DEFAULT     1 secure_entry
+// CHECK1-NEXT:      5: 00020001     8 FUNC    GLOBAL DEFAULT     2 foo
+// CHECK1-NEXT:      6: 00008005     2 FUNC    GLOBAL DEFAULT     1 __acle_se_foo
+// CHECK1-NEXT:      7: 00020009     8 FUNC    WEAK   DEFAULT     2 bar
+// CHECK1-NEXT:      8: 00008009     2 FUNC    GLOBAL DEFAULT     1 __acle_se_bar
+// CHECK1-NEXT:      9: 0000800d     8 FUNC    WEAK   DEFAULT     1 no_veneer1
+// CHECK1-NEXT:     10: 00008013     2 FUNC    GLOBAL DEFAULT     1 __acle_se_no_veneer1
+// CHECK1-NEXT:     11: 00008015     8 FUNC    WEAK   DEFAULT     1 no_veneer2
+// CHECK1-NEXT:     12: 0000801b     2 FUNC    WEAK   DEFAULT     1 __acle_se_no_veneer2
+
+
+/// Import library 1
+// CHECK1:      File:
+// CHECK1:      Symbol table '.symtab' contains 5 entries:
+// CHECK1-NEXT:    Num:    Value  Size Type    Bind   Vis       Ndx Name
+// CHECK1-NEXT:      0: 00000000     0 NOTYPE  LOCAL  DEFAULT   UND
+// CHECK1-NEXT:      1: 00020009     8 FUNC    WEAK   DEFAULT   ABS bar
+// CHECK1-NEXT:      2: 00020001     8 FUNC    GLOBAL DEFAULT   ABS foo
+// CHECK1-NEXT:      3: 0000800d     8 FUNC    WEAK   DEFAULT   ABS no_veneer1
+// CHECK1-NEXT:      4: 00008015     8 FUNC    WEAK   DEFAULT   ABS no_veneer2
+
+/// Executable 2
+// CHECK2:      File:
+// CHECK2:      Symbol table '.symtab' contains 15 entries:
+// CHECK2-NEXT:    Num:    Value  Size Type    Bind   Vis       Ndx Name
+// CHECK2-NEXT:      0: 00000000     0 NOTYPE  LOCAL  DEFAULT   UND
+// CHECK2-NEXT:      1: 00020000     0 NOTYPE  LOCAL  DEFAULT     2 $t
+// CHECK2-NEXT:      2: 00008000     0 NOTYPE  LOCAL  DEFAULT     1 $t.0
+// CHECK2-NEXT:      3: 00008004     0 NOTYPE  LOCAL  DEFAULT     1 $t.0
+// CHECK2-NEXT:      4: 00008001     2 FUNC    GLOBAL DEFAULT     1 secure_entry
+// CHECK2-NEXT:      5: 00020019     8 FUNC    WEAK   DEFAULT     2 baz
+// CHECK2-NEXT:      6: 00008005     2 FUNC    GLOBAL DEFAULT     1 __acle_se_baz
+// CHECK2-NEXT:      7: 00020001     8 FUNC    GLOBAL DEFAULT     2 foo
+// CHECK2-NEXT:      8: 00008009     2 FUNC    GLOBAL DEFAULT     1 __acle_se_foo
+// CHECK2-NEXT:      9: 00020011     8 FUNC    GLOBAL DEFAULT     2 qux
+// CHECK2-NEXT:     10: 0000800d     2 FUNC    GLOBAL DEFAULT     1 __acle_se_qux
+// CHECK2-NEXT:     11: 00008011     8 FUNC    WEAK   DEFAULT     1 no_veneer1
+// CHECK2-NEXT:     12: 00008017     2 FUNC    GLOBAL DEFAULT     1 __acle_se_no_veneer1
+// CHECK2-NEXT:     13: 00008019     8 FUNC    WEAK   DEFAULT     1 no_veneer2
+// CHECK2-NEXT:     14: 0000801f     2 FUNC    WEAK   DEFAULT     1 __acle_se_no_veneer2
+
+
+/// Note that foo retains its address from Import library 1 (0x000020009)
+/// New entry functions, baz and qux, use addresses not used by Import library 1.
+/// Import library 2
+// CHECK2:      File:
+// CHECK2:      Symbol table '.symtab' contains 6 entries:
+// CHECK2-NEXT:    Num:    Value  Size Type    Bind   Vis       Ndx Name
+// CHECK2-NEXT:      0: 00000000     0 NOTYPE  LOCAL  DEFAULT   UND
+// CHECK2-NEXT:      1: 00020019     8 FUNC    WEAK   DEFAULT   ABS baz
+// CHECK2-NEXT:      2: 00020001     8 FUNC    GLOBAL DEFAULT   ABS foo
+// CHECK2-NEXT:      3: 00008011     8 FUNC    WEAK   DEFAULT   ABS no_veneer1
+// CHECK2-NEXT:      4: 00008019     8 FUNC    WEAK   DEFAULT   ABS no_veneer2
+// CHECK2-NEXT:      5: 00020011     8 FUNC    GLOBAL DEFAULT   ABS qux
diff --git a/lld/test/ELF/arm-cmse-invalid-arch.s b/lld/test/ELF/arm-cmse-invalid-arch.s
new file mode 100644
--- /dev/null
+++ b/lld/test/ELF/arm-cmse-invalid-arch.s
@@ -0,0 +1,37 @@
+// REQUIRES: arm
+
+/// CMSE Only supported by ARMv8-M architecture or later.
+// RUN: llvm-mc -arm-add-build-attributes -filetype=obj -triple=thumbv8m.base %s -I %S/Inputs -o %t1.o
+// RUN: ld.lld --cmse-implib -Ttext=0x8000 --section-start .gnu.sgstubs=0x20000 -o %t1 %t1.o
+
+// RUN: llvm-mc -arm-add-build-attributes -filetype=obj -triple=thumbv8m.main %s -I %S/Inputs -o %t2.o
+// RUN: ld.lld --cmse-implib -Ttext=0x8000 --section-start .gnu.sgstubs=0x20000 -o %t2 %t2.o
+
+// RUN: llvm-mc -arm-add-build-attributes -filetype=obj -triple=thumbv8.1m.main %s -I %S/Inputs -o %t3.o
+// RUN: ld.lld --cmse-implib -Ttext=0x8000 --section-start .gnu.sgstubs=0x20000 -o %t3 %t3.o
+
+// RUN: llvm-mc -arm-add-build-attributes -filetype=obj -triple=thumbv9a %s -I %S/Inputs -o %t4.o
+// RUN: ld.lld --cmse-implib -Ttext=0x8000 --section-start .gnu.sgstubs=0x20000 -o %t4 %t4.o
+
+/// Expect errors for other architectures
+// RUN: llvm-mc -arm-add-build-attributes -filetype=obj -triple=armv7-m %s -I %S/Inputs -o %t5.o
+// RUN: not ld.lld --cmse-implib -Ttext=0x8000 --section-start .gnu.sgstubs=0x20000 -o %t5 %t5.o 2>&1 | FileCheck %s --check-prefix=ERROR
+
+// RUN: llvm-mc -arm-add-build-attributes -filetype=obj -triple=armv8-m %s -I %S/Inputs -o %t6.o
+// RUN: not ld.lld --cmse-implib -Ttext=0x8000 --section-start .gnu.sgstubs=0x20000 -o %t6 %t6.o 2>&1 | FileCheck %s --check-prefix=ERROR
+
+/// Invalid triple defaults to v4T. Error.
+// RUN: llvm-mc -arm-add-build-attributes -filetype=obj -triple=thumb %s -I %S/Inputs -o %t7.o
+// RUN: not ld.lld --cmse-implib -Ttext=0x8000 --section-start .gnu.sgstubs=0x20000 -o %t7 %t7.o  2>&1 | FileCheck %s --check-prefix=ERROR
+
+/// No build attributes. Error.
+// RUN: llvm-mc -filetype=obj -triple=thumb %s -I %S/Inputs -o %t8.o
+// RUN: not ld.lld --cmse-implib -Ttext=0x8000 --section-start .gnu.sgstubs=0x20000 -o %t8 %t8.o  2>&1 | FileCheck %s --check-prefix=ERROR
+
+  .include "arm-cmse-macros.s"
+  .text
+  .thumb
+
+cmse_veneer entry, function, global, function, global
+
+// ERROR: cmse special symbol '__acle_se_entry' only allowed for ARMv8-M architecture or later
diff --git a/lld/test/ELF/arm-cmse-noveneers.s b/lld/test/ELF/arm-cmse-noveneers.s
new file mode 100644
--- /dev/null
+++ b/lld/test/ELF/arm-cmse-noveneers.s
@@ -0,0 +1,30 @@
+/// Test that addresses of existing secure gateway veneers are output in the CMSE import library.
+/// Test that .gnu.sgstubs is size 0 when no linker synthesized secure gateway veneers are created.
+
+// REQUIRES: arm
+// RUN: llvm-mc -arm-add-build-attributes -filetype=obj --triple=thumbv8m.main %s -I %S/Inputs -o %t.o
+// RUN: ld.lld --cmse-implib -Ttext=0x8000 --section-start .gnu.sgstubs=0x20000 %t.o -o %t --out-implib=%t.lib
+// RUN: llvm-objdump -d %t | FileCheck %s
+// RUN: llvm-readelf -S %t | FileCheck %s --check-prefix=SGSTUBSSIZE
+// RUN: llvm-readelf -s %t.lib | FileCheck %s --check-prefix=IMPLIBSYMS
+
+// CHECK: Disassembly of section .text:
+
+// CHECK:      00008000 <existing_veneer>:
+// CHECK-NEXT:     8000: e97f e97f    	sg
+// CHECK-NEXT:     8004: bf00         	nop
+
+// CHECK:      00008006 <__acle_se_existing_veneer>:
+// CHECK-NEXT:     8006: bf00         	nop
+
+ .include "arm-cmse-macros.s"
+
+  cmse_no_veneer existing_veneer, function, global, function, global
+
+///                      Name          Type         Address    Off   Size ES Flg Lk Inf Al
+// SGSTUBSSIZE: .gnu.sgstubs      PROGBITS        00020000 020000 000000 08  AX  0   0 32
+
+// IMPLIBSYMS:      Symbol table '.symtab' contains 2 entries:
+// IMPLIBSYMS-NEXT:    Num:    Value  Size Type    Bind   Vis       Ndx Name
+// IMPLIBSYMS-NEXT:      0: 00000000     0 NOTYPE  LOCAL  DEFAULT   UND
+// IMPLIBSYMS-NEXT:      1: 00008001     8 FUNC    GLOBAL DEFAULT   ABS existing_veneer
diff --git a/lld/test/ELF/arm-cmse-secure.s b/lld/test/ELF/arm-cmse-secure.s
new file mode 100644
--- /dev/null
+++ b/lld/test/ELF/arm-cmse-secure.s
@@ -0,0 +1,65 @@
+// REQUIRES: arm
+// RUN: split-file %s %t
+// RUN: llvm-mc -arm-add-build-attributes -filetype=obj --triple=thumbv8m.main %t/cmse-implib.s -o %timplib.o -I%S/Inputs/
+// RUN: llvm-mc -arm-add-build-attributes -filetype=obj --triple=thumbv8m.main %t/cmse-secure-app.s -o %tsecureapp.o
+// RUN: llvm-mc -arm-add-build-attributes -filetype=obj --triple=thumbv8m.main %t/cmse-non-secure-app.s -o %tnonsecureapp.o
+/// Create the secure app and import library.
+// RUN: ld.lld --entry=secure_entry --section-start .gnu.sgstubs=0x20000 --cmse-implib %timplib.o %tsecureapp.o --out-implib=%timplib.lib -o %tsecureapp
+/// Link the non-secure app against the import library
+// RUN: ld.lld --entry=nonsecure_entry -Ttext=0x8000 -o %t1 --in-implib=%timplib.lib --cmse-implib %tnonsecureapp.o -o %tnonsecureapp
+// RUN: llvm-readelf -s %timplib.lib | FileCheck %s
+// RUN: llvm-objdump -D %tsecureapp | FileCheck %s --check-prefix=SECUREDISS
+// RUN: llvm-objdump -D %tnonsecureapp | FileCheck %s --check-prefix=NONSECUREDISS
+
+// SECUREDISS:      00020000 <entry>:
+// SECUREDISS-NEXT:    20000: e97f e97f      sg
+// SECUREDISS-NEXT:    20004: f000 b800      b.w  0x20008 <__acle_se_entry>
+
+// SECUREDISS:      00020008 <__acle_se_entry>:
+// SECUREDISS-NEXT:    20008: bf00            nop
+
+// SECUREDISS:      0002000c <secure_entry>:
+// SECUREDISS-NEXT:    2000c: f7ff fff8    	bl	0x20000
+// SECUREDISS-NEXT:    20010: 4770         	bx	lr
+
+// NONSECUREDISS:   00008000 <nonsecure_entry>:
+// NONSECUREDISS-NEXT:  8000: b501         	push	{r0, lr}
+// NONSECUREDISS-NEXT:  8002: f017 fffd    	bl	0x20000
+// NONSECUREDISS-NEXT:  8006: e8bd 4001    	pop.w	{r0, lr}
+// NONSECUREDISS-NEXT:  800a: 4770         	bx	lr
+
+//--- cmse-implib.s
+  .include "arm-cmse-macros.s"
+
+  .syntax unified
+  .text
+
+  cmse_veneer entry, function, global, function, global
+
+//--- cmse-secure-app.s
+  .align  2
+    // Main entry point.
+    .global secure_entry
+    .thumb_func
+secure_entry:
+    bl entry
+    bx lr
+  .size  secure_entry, .-secure_entry
+
+//--- cmse-non-secure-app.s
+  .align  2
+  .global nonsecure_entry
+  .thumb
+  .thumb_func
+  .type  nonsecure_entry, %function
+nonsecure_entry:
+  push {r0,lr}
+  bl entry
+  pop {r0,lr}
+  bx lr
+  .size  nonsecure_entry, .-nonsecure_entry
+
+// CHECK:      Symbol table '.symtab' contains 2 entries:
+// CHECK-NEXT:    Num:    Value  Size Type    Bind   Vis       Ndx Name
+// CHECK-NEXT:      0: 00000000     0 NOTYPE  LOCAL  DEFAULT   UND
+// CHECK-NEXT:      1: 00020001     8 FUNC    GLOBAL DEFAULT   ABS entry
diff --git a/lld/test/ELF/arm-cmse-veneers.s b/lld/test/ELF/arm-cmse-veneers.s
new file mode 100644
--- /dev/null
+++ b/lld/test/ELF/arm-cmse-veneers.s
@@ -0,0 +1,35 @@
+// REQUIRES: arm
+// RUN: llvm-mc -arm-add-build-attributes -filetype=obj --triple=thumbv8m.main %s -I %S/Inputs -o %t.o
+// RUN: ld.lld --cmse-implib -Ttext=0x8000 --section-start .gnu.sgstubs=0x20000 %t.o -o %t
+// RUN: llvm-objdump -d %t | FileCheck %s
+
+// CHECK: Disassembly of section .text:
+// CHECK: 00008000 <__acle_se_global_foo>
+// CHECK: 00008004 <__acle_se_weak_bar>
+// CHECK: 00008008 <__acle_se_global_baz>
+// CHECK: 0000800c <__acle_se_weak_qux>
+
+// CHECK: Disassembly of section .gnu.sgstubs:
+
+// CHECK:      00020000 <weak_qux>:
+// CHECK-NEXT:    20000: e97f e97f    	sg
+// CHECK-NEXT:    20004: f7e8 b802    	b.w	0x800c <__acle_se_weak_qux>
+
+// CHECK:      00020008 <weak_bar>:
+// CHECK-NEXT:    20008: e97f e97f    	sg
+// CHECK-NEXT:    2000c: f7e7 bffa    	b.w	0x8004 <__acle_se_weak_bar>
+
+// CHECK:      00020010 <global_foo>:
+// CHECK-NEXT:    20010: e97f e97f    	sg
+// CHECK-NEXT:    20014: f7e7 bff4    	b.w	0x8000 <__acle_se_global_foo>
+
+// CHECK:      00020018 <global_baz>:
+// CHECK-NEXT:    20018: e97f e97f    	sg
+// CHECK-NEXT:    2001c: f7e7 bff4    	b.w	0x8008 <__acle_se_global_baz>
+
+  .include "arm-cmse-macros.s"
+
+  cmse_veneer global_foo, function, global, function, global
+  cmse_veneer weak_bar, function, weak, function, weak
+  cmse_veneer global_baz, function, global, function, weak
+  cmse_veneer weak_qux, function, weak, function, global