[ELF] Allow specifying the stack size

[phosek]

Summary

This option can be used to set the size of the initial stack by setting the size of the PT_GNU_STACK segment.

[ruiu]

LGTM with nits.

ELF/Config.h

117

Sort.

ELF/Driver.cpp

260

getZOptionValue would be a better name because this function returns a value.

264–265

You can merge the two ifs.

413

Nit: remove {}.

test/ELF/zstack-size.s

12–48

These program headers are not relevant, so please remove.

[phosek]

ELF/Config.h

117

Isn't this already sorted (relative to other Z fields)?

[ruiu]

LGTM wtih this change.

ELF/Config.h

117

But other members are sorted by type, too. See ImageBase below.

[phosek]

ELF/Config.h

117

I missed the sorting by type.

ELF/Config.h

struct Configuration {
   bool Verbose;
   bool WarnCommon;
   bool ZCombreloc;
   bool ZExecStack;
   bool ZNodelete;
   bool ZNow;
   bool ZOrigin;
   bool ZRelro;
   UnresolvedPolicy UnresolvedSymbols;
   BuildIdKind BuildId = BuildIdKind::None;
   ELFKind EKind = ELFNoneKind;
   uint16_t DefaultSymbolVersion = llvm::ELF::VER_NDX_GLOBAL;
   uint16_t EMachine = llvm::ELF::EM_NONE;
   uint64_t EntryAddr = -1;
   uint64_t ImageBase;
+  uint64_t ZStackSize = -1;
   unsigned LtoJobs;
   unsigned LtoO;
   unsigned Optimize;
 };
 
 // The only instance of Configuration struct.
 extern Configuration *Config;
 
 } // namespace elf
 } // namespace lld
 
 #endif

ELF/Driver.cpp

 
 static bool hasZOption(opt::InputArgList &Args, StringRef Key) {
   for (auto *Arg : Args.filtered(OPT_z))
     if (Key == Arg->getValue())
       return true;
   return false;
 }
 
+static Optional<StringRef>
+getZOptionValue(opt::InputArgList &Args, StringRef Key) {
+  for (auto *Arg : Args.filtered(OPT_z)) {
+    StringRef Value = Arg->getValue();
+    size_t Pos = Value.find("=");
+    if (Pos != StringRef::npos && Key == Value.substr(0, Pos))
+      return Value.substr(Pos + 1);
+  }
+  return None;
+}
+
 void LinkerDriver::main(ArrayRef<const char *> ArgsArr) {
   ELFOptTable Parser;
   opt::InputArgList Args = Parser.parse(ArgsArr.slice(1));
   if (Args.hasArg(OPT_help)) {
     printHelp(ArgsArr[0]);
     return;
   }
   if (Args.hasArg(OPT_version))
void LinkerDriver::readConfigs(opt::InputArgList &Args) {
 
   Config->ZCombreloc = !hasZOption(Args, "nocombreloc");
   Config->ZExecStack = hasZOption(Args, "execstack");
   Config->ZNodelete = hasZOption(Args, "nodelete");
   Config->ZNow = hasZOption(Args, "now");
   Config->ZOrigin = hasZOption(Args, "origin");
   Config->ZRelro = !hasZOption(Args, "norelro");
 
+  if (Optional<StringRef> Value = getZOptionValue(Args, "stack-size"))
+    if (Value->getAsInteger(0, Config->ZStackSize))
+      error("invalid stack size: " + *Value);
+
   if (Config->Relocatable)
     Config->StripAll = false;
 
   // --strip-all implies --strip-debug.
   if (Config->StripAll)
     Config->StripDebug = true;
 
   // Config->Pic is true if we are generating position-independent code.
   Config->Pic = Config->Pie || Config->Shared;

ELF/Writer.cpp

std::vector<PhdrEntry<ELFT>> Writer<ELFT>::createPhdrs() {
   // PT_GNU_EH_FRAME is a special section pointing on .eh_frame_hdr.
   if (!Out<ELFT>::EhFrame->empty() && Out<ELFT>::EhFrameHdr) {
     Phdr &Hdr = *AddHdr(PT_GNU_EH_FRAME, Out<ELFT>::EhFrameHdr->getPhdrFlags());
     Hdr.add(Out<ELFT>::EhFrameHdr);
   }
 
   // PT_GNU_STACK is a special section to tell the loader to make the
   // pages for the stack non-executable.
-  if (!Config->ZExecStack)
-    AddHdr(PT_GNU_STACK, PF_R | PF_W);
+  if (!Config->ZExecStack) {
+    Phdr &Hdr = *AddHdr(PT_GNU_STACK, PF_R | PF_W);
+    if (Config->ZStackSize != uint64_t(-1))
+      Hdr.H.p_memsz = Config->ZStackSize;
+  }
 
   if (Note.First)
     Ret.push_back(std::move(Note));
   return Ret;
 }
 
 // The first section of each PT_LOAD and the first section after PT_GNU_RELRO
 // have to be page aligned so that the dynamic linker can set the permissions.

test/ELF/zstack-size.s

+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
+# RUN: ld.lld -z stack-size=0x1000 %t -o %t1
+# RUN: llvm-readobj -program-headers %t1 | FileCheck %s
+
+.global _start
+_start:
+  nop
+
+# CHECK:     Type: PT_GNU_STACK (0x6474E551)
+# CHECK-NEXT:     Offset: 0x0
+# CHECK-NEXT:     VirtualAddress: 0x0
+# CHECK-NEXT:     PhysicalAddress: 0x0
+# CHECK-NEXT:     FileSize: 0
+# CHECK-NEXT:     MemSize: 4096
+# CHECK-NEXT:     Flags [ (0x6)
+# CHECK-NEXT:       PF_R (0x4)
+# CHECK-NEXT:       PF_W (0x2)
+# CHECK-NEXT:     ]
+# CHECK-NEXT:     Alignment: 0