[llvm-objcopy]Add support for *-freebsd output formats

[jhenderson]

Summary

GNU objcopy can support output formats like elf32-i386-freebsd and elf64-x86-64-freebsd. The only difference from their regular non-freebsd counterparts that I have observed is that the freebsd versions set the OS/ABI field to ELFOSABI_FREEBSD. This patch sets the OS/ABI field accordingly whenever --output-format is specified.

[rupprecht]

The objcopy on my machine doesn't seem to be built w/ the freebsd bfd targets enabled, so I can't repro, but this seems fine. Two interesting things I found while comparing against the source:

1. For older FreeBSDs (<= 4.0), objcopy actually copies the string "FreeBSD" into e_ident [1]. This seems to work because there's enough padding bytes. (I suggest we don't do this, but I found it to be interesting trivia).
2. In the method that actually sets the OSABI member [2], if the OSABI field is still ELFOSABI_NONE, it will change it to ELFOSABI_GNU if the object contains GNU symbols. Does this seem useful to do?

12065   /* To make things simpler for the loader on Linux systems we set the
12066      osabi field to ELFOSABI_GNU if the binary contains symbols of
12067      the STT_GNU_IFUNC type or STB_GNU_UNIQUE binding.  */
12068   if (i_ehdrp->e_ident[EI_OSABI] == ELFOSABI_NONE
12069       && elf_tdata (abfd)->has_gnu_symbols)
12070     i_ehdrp->e_ident[EI_OSABI] = ELFOSABI_GNU;

[1] https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=blob;f=bfd/elf32-i386.c;h=79cd8c65bc150781b9783cfc591b08fc36785890;hb=HEAD#l4414
[2] https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=blob;f=bfd/elf.c;h=73fb86971f3dcc0461ba17d5d24d3cf7add41761;hb=HEAD#l12055

[jhenderson]

In D59645#1438161, @rupprecht wrote:

In the method that actually sets the OSABI member [2], if the OSABI field is still ELFOSABI_NONE, it will change it to ELFOSABI_GNU if the object contains GNU symbols. Does this seem useful to do?

It does seem somewhat useful, but it looks like a different, only tangetially-related, behaviour, so I'll file a bug for that, especially as I imagine it will slow down the tool (it'll have to keep track of all symbols that are GNU symbols).

[grimar]

LGTM too.

[grimar]

tools/llvm-objcopy/ELF/ELFObjcopy.cpp

229

Oh. Was this place tested? Seems not.

[jhenderson]

tools/llvm-objcopy/ELF/ELFObjcopy.cpp

229

Yeah, I noticed this when I was uploading this patch. I've got a note on my desk to look at adding a test for this section (the Machine line immediately above it is also untested). Given the block is already untested, are you happy for this to be tested in a separate patch, or would you prefer it being part of this one?

[grimar]

tools/llvm-objcopy/ELF/ELFObjcopy.cpp

229

Given the block is already untested, are you happy for this to be tested in a separate patch, or would you prefer it being part of this one?

I think it's fine to do in a separate patch then.

[jhenderson]

I've filed https://bugs.llvm.org/show_bug.cgi?id=41196 for the GNU OSABI issue, and created D59691 for the test coverage addition.

test/tools/llvm-objcopy/ELF/binary-input-with-arch.test

 # RUN: echo -n abcd > %t.x-txt
 # Preserve input to verify it is not modified.
 # RUN: cp %t.x-txt %t-copy.txt
 # RUN: llvm-objcopy -I binary -B i386 -O elf64-x86-64 %t.x-txt %t.o
-# RUN: llvm-readobj --file-headers %t.o | FileCheck %s
+# RUN: llvm-readobj --file-headers %t.o | FileCheck %s --check-prefixes=CHECK,SYSV
 # RUN: cmp %t.x-txt %t-copy.txt
 
 # Many uses of objcopy use no spaces in the flags, make sure that also works.
 # RUN: llvm-objcopy -Ibinary -Bi386 -Oelf64-x86-64 %t.x-txt %t-no-spaces.o
 # RUN: cmp %t.o %t-no-spaces.o
 
+# elf64-x86-64-freebsd sets the OS/ABI field.
+# RUN: llvm-objcopy -I binary -B i386 -O elf64-x86-64-freebsd %t.x-txt %t.freebsd.o
+# RUN: llvm-readobj --file-headers %t.freebsd.o | FileCheck %s --check-prefixes=CHECK,FREEBSD
+
 # CHECK:      Format: ELF64-x86-64
 # CHECK-NEXT: Arch: x86_64
 # CHECK-NEXT: AddressSize: 64bit
 
 # CHECK: Class: 64-bit
 # CHECK: DataEncoding: LittleEndian
+# SYSV:    OS/ABI: SystemV
+# FREEBSD: OS/ABI: FreeBSD
 # CHECK: Machine: EM_X86_64
 # CHECK: HeaderSize: 64
 # CHECK: SectionHeaderEntrySize: 64

test/tools/llvm-objcopy/ELF/cross-arch-headers.test

 # RUN: yaml2obj %s > %t.o
 
 # RUN: llvm-objcopy %t.o -O elf32-i386 %t.elf32_i386.o
-# RUN: llvm-readobj --file-headers %t.elf32_i386.o | FileCheck %s --check-prefixes=CHECK,I386,32
+# RUN: llvm-readobj --file-headers %t.elf32_i386.o | FileCheck %s --check-prefixes=CHECK,I386,32,SYSV
 
 # RUN: llvm-objcopy %t.o -O elf32-powerpcle %t.elf32_ppcle.o
-# RUN: llvm-readobj --file-headers %t.elf32_ppcle.o | FileCheck %s --check-prefixes=CHECK,PPC,32
+# RUN: llvm-readobj --file-headers %t.elf32_ppcle.o | FileCheck %s --check-prefixes=CHECK,PPC,32,SYSV
 
 # RUN: llvm-objcopy %t.o -O elf32-x86-64 %t.elf32_x86_64.o
-# RUN: llvm-readobj --file-headers %t.elf32_x86_64.o | FileCheck %s --check-prefixes=CHECK,X86-64,32
+# RUN: llvm-readobj --file-headers %t.elf32_x86_64.o | FileCheck %s --check-prefixes=CHECK,X86-64,32,SYSV
 
 # RUN: llvm-objcopy %t.o -O elf64-powerpcle %t.elf64_ppcle.o
-# RUN: llvm-readobj --file-headers %t.elf64_ppcle.o | FileCheck %s --check-prefixes=CHECK,PPC64,64
+# RUN: llvm-readobj --file-headers %t.elf64_ppcle.o | FileCheck %s --check-prefixes=CHECK,PPC64,64,SYSV
 
 # RUN: llvm-objcopy %t.o -O elf64-x86-64 %t.elf64_x86_64.o
-# RUN: llvm-readobj --file-headers %t.elf64_x86_64.o | FileCheck %s --check-prefixes=CHECK,X86-64,64
+# RUN: llvm-readobj --file-headers %t.elf64_x86_64.o | FileCheck %s --check-prefixes=CHECK,X86-64,64,SYSV
+
+# RUN: llvm-objcopy %t.o -O elf64-x86-64-freebsd %t.elf64_x86_64_freebsd.o
+# RUN: llvm-readobj --file-headers %t.elf64_x86_64_freebsd.o | FileCheck %s --check-prefixes=CHECK,X86-64,64,FREEBSD
+
+# RUN: llvm-objcopy %t.o -O elf32-i386-freebsd %t.elf32_i386_freebsd.o
+# RUN: llvm-readobj --file-headers %t.elf32_i386_freebsd.o | FileCheck %s --check-prefixes=CHECK,I386,32,FREEBSD
 
 !ELF
 FileHeader:
   Class:           ELFCLASS32
   Data:            ELFDATA2LSB
   Type:            ET_EXEC
   Machine:         EM_386
+  OSABI:           ELFOSABI_STANDALONE # Arbitrary non-zero value.
 Sections:
   - Name:            .text
     Type:            SHT_PROGBITS
     Flags:           [ SHF_ALLOC, SHF_EXECINSTR ]
   - Name:            .data
     Type:            SHT_PROGBITS
     Flags:           [ SHF_ALLOC ]
 Symbols:

 
 # 32-NEXT:      AddressSize: 32bit
 # 64-NEXT:      AddressSize: 64bit
 
 # 32:     Class: 32-bit
 # 64:     Class: 64-bit
 # CHECK:  DataEncoding: LittleEndian
 
+# SYSV:    OS/ABI: SystemV (0x0)
+# FREEBSD: OS/ABI: FreeBSD (0x9)
+
 # I386:   Machine: EM_386
 # PPC:    Machine: EM_PPC
 # PPC64:  Machine: EM_PPC64
 # X86-64: Machine: EM_X86_64
 
 # 32: HeaderSize: 52
 # 64: HeaderSize: 64
 
 # 32: SectionHeaderEntrySize: 40
 # 64: SectionHeaderEntrySize: 64

tools/llvm-objcopy/CopyConfig.h

 namespace llvm {
 namespace objcopy {
 
 // This type keeps track of the machine info for various architectures. This
 // lets us map architecture names to ELF types and the e_machine value of the
 // ELF file.
 struct MachineInfo {
   uint16_t EMachine;
+  uint8_t OSABI;
   bool Is64Bit;
   bool IsLittleEndian;
 };
 
 struct SectionRename {
   StringRef OriginalName;
   StringRef NewName;
   Optional<uint64_t> NewFlags;

tools/llvm-objcopy/CopyConfig.cpp

if (!UnsupportedFlags.empty())
     return createStringError(errc::invalid_argument,
                              "unsupported flag%s for --add-symbol: '%s'",
                              UnsupportedFlags.size() > 1 ? "s" : "",
                              join(UnsupportedFlags, "', '").c_str());
   return SI;
 }
 
 static const StringMap<MachineInfo> ArchMap{
-    // Name, {EMachine, 64bit, LittleEndian}
-    {"aarch64", {ELF::EM_AARCH64, true, true}},
-    {"arm", {ELF::EM_ARM, false, true}},
-    {"i386", {ELF::EM_386, false, true}},
-    {"i386:x86-64", {ELF::EM_X86_64, true, true}},
-    {"powerpc:common64", {ELF::EM_PPC64, true, true}},
-    {"sparc", {ELF::EM_SPARC, false, true}},
-    {"x86-64", {ELF::EM_X86_64, true, true}},
+    // Name, {EMachine, OS/ABI, 64bit, LittleEndian}
+    {"aarch64", {ELF::EM_AARCH64, ELF::ELFOSABI_NONE, true, true}},
+    {"arm", {ELF::EM_ARM, ELF::ELFOSABI_NONE, false, true}},
+    {"i386", {ELF::EM_386, ELF::ELFOSABI_NONE, false, true}},
+    {"i386:x86-64", {ELF::EM_X86_64, ELF::ELFOSABI_NONE, true, true}},
+    {"powerpc:common64", {ELF::EM_PPC64, ELF::ELFOSABI_NONE, true, true}},
+    {"sparc", {ELF::EM_SPARC, ELF::ELFOSABI_NONE, false, true}},
+    {"x86-64", {ELF::EM_X86_64, ELF::ELFOSABI_NONE, true, true}},
 };
 
 static Expected<const MachineInfo &> getMachineInfo(StringRef Arch) {
   auto Iter = ArchMap.find(Arch);
   if (Iter == std::end(ArchMap))
     return createStringError(errc::invalid_argument,
                              "Invalid architecture: '%s'", Arch.str().c_str());
   return Iter->getValue();
 }
 
 static const StringMap<MachineInfo> OutputFormatMap{
-    // Name, {EMachine, 64bit, LittleEndian}
-    {"elf32-i386", {ELF::EM_386, false, true}},
-    {"elf32-powerpcle", {ELF::EM_PPC, false, true}},
-    {"elf32-x86-64", {ELF::EM_X86_64, false, true}},
-    {"elf64-powerpcle", {ELF::EM_PPC64, true, true}},
-    {"elf64-x86-64", {ELF::EM_X86_64, true, true}},
+    // Name, {EMachine, OSABI, 64bit, LittleEndian}
+    {"elf32-i386", {ELF::EM_386, ELF::ELFOSABI_NONE, false, true}},
+    {"elf32-i386-freebsd", {ELF::EM_386, ELF::ELFOSABI_FREEBSD, false, true}},
+    {"elf32-powerpcle", {ELF::EM_PPC, ELF::ELFOSABI_NONE, false, true}},
+    {"elf32-x86-64", {ELF::EM_X86_64, ELF::ELFOSABI_NONE, false, true}},
+    {"elf64-powerpcle", {ELF::EM_PPC64, ELF::ELFOSABI_NONE, true, true}},
+    {"elf64-x86-64", {ELF::EM_X86_64, ELF::ELFOSABI_NONE, true, true}},
+    {"elf64-x86-64-freebsd",
+     {ELF::EM_X86_64, ELF::ELFOSABI_FREEBSD, true, true}},
 };
 
 static Expected<const MachineInfo &>
 getOutputFormatMachineInfo(StringRef Format) {
   auto Iter = OutputFormatMap.find(Format);
   if (Iter == std::end(OutputFormatMap))
     return createStringError(errc::invalid_argument,
                              "Invalid output format: '%s'",

tools/llvm-objcopy/ELF/ELFObjcopy.cpp

 static Error splitDWOToFile(const CopyConfig &Config, const Reader &Reader,
                             StringRef File, ElfType OutputElfType) {
   auto DWOFile = Reader.create();
   auto OnlyKeepDWOPred = [&DWOFile](const SectionBase &Sec) {
     return onlyKeepDWOPred(*DWOFile, Sec);
   };
   if (Error E = DWOFile->removeSections(OnlyKeepDWOPred))
     return E;
-  if (Config.OutputArch)
+  if (Config.OutputArch) {
     DWOFile->Machine = Config.OutputArch.getValue().EMachine;
+    DWOFile->OSABI = Config.OutputArch.getValue().OSABI;
+  }
   FileBuffer FB(File);
   auto Writer = createWriter(Config, *DWOFile, FB, OutputElfType);
   if (Error E = Writer->finalize())
     return E;
   return Writer->write();
 }
 
 static Error dumpSectionToFile(StringRef SecName, StringRef Filename,

 static Error handleArgs(const CopyConfig &Config, Object &Obj,
                         const Reader &Reader, ElfType OutputElfType) {
 
   if (!Config.SplitDWO.empty())
     if (Error E =
             splitDWOToFile(Config, Reader, Config.SplitDWO, OutputElfType))
       return E;
 
-  if (Config.OutputArch)
+  if (Config.OutputArch) {
     Obj.Machine = Config.OutputArch.getValue().EMachine;
+    Obj.OSABI = Config.OutputArch.getValue().OSABI;
+  }
 
   // TODO: update or remove symbols only if there is an option that affects
   // them.
   if (Obj.SymbolTable) {
     Obj.SymbolTable->updateSymbols([&](Symbol &Sym) {
       // Common and undefined symbols don't make sense as local symbols, and can
       // even cause crashes if we localize those, so skip them.
       if (!Sym.isCommon() && Sym.getShndx() != SHN_UNDEF &&