lld: Add -m elf32_x86_64

[hjl.tools]

Summary

This patch adds -m elf32_x86_64 to lld. But it doesn't generate working
x32 binaries.

[davide]

LGTM modulo nit.
For the future, please upload a diff with context, so that we can review directly on phab.
svn diff --diff-cmd=diff -x-U50000 or git diff -U50000

Thanks for the patch!

ELF/Driver.cpp

73 ↗

(On Diff #63690)

This is unsorted, maybe.

[ruiu]

Can you create working x32 executables with this patch? I expected a small change, but this is smaller than I imagined. For example, it would create PLTs exactly the same as the x86-64 ABI. I'm wondering if it was expected.

[hjl.tools]

This patches fixes PLTREL. But it doesn't generate working x32 binaries.

[ruiu]

LGTM, but please update the commit message to say that this is an initial patch for x32 and more work is needed to create working x32 binaries.

lld/trunk/ELF/Driver.cpp

 static std::pair<ELFKind, uint16_t> parseEmulation(StringRef S) {
   if (S.endswith("_fbsd"))
     S = S.drop_back(5);
 
   std::pair<ELFKind, uint16_t> Ret =
       StringSwitch<std::pair<ELFKind, uint16_t>>(S)
           .Case("aarch64linux", {ELF64LEKind, EM_AARCH64})
           .Case("armelf_linux_eabi", {ELF32LEKind, EM_ARM})
+          .Case("elf32_x86_64", {ELF32LEKind, EM_X86_64})
           .Case("elf32btsmip", {ELF32BEKind, EM_MIPS})
           .Case("elf32ltsmip", {ELF32LEKind, EM_MIPS})
           .Case("elf32ppc", {ELF32BEKind, EM_PPC})
           .Case("elf64btsmip", {ELF64BEKind, EM_MIPS})
           .Case("elf64ltsmip", {ELF64LEKind, EM_MIPS})
           .Case("elf64ppc", {ELF64BEKind, EM_PPC64})
           .Case("elf_i386", {ELF32LEKind, EM_386})
           .Case("elf_x86_64", {ELF64LEKind, EM_X86_64})
template <class ELFT> void LinkerDriver::link(opt::InputArgList &Args) {
   SymbolTable<ELFT> Symtab;
   elf::Symtab<ELFT>::X = &Symtab;
 
   std::unique_ptr<TargetInfo> TI(createTarget());
   Target = TI.get();
   LinkerScript<ELFT> LS;
   Script<ELFT>::X = &LS;
 
-  Config->Rela = ELFT::Is64Bits;
+  Config->Rela = ELFT::Is64Bits || Config->EMachine == EM_X86_64;
   Config->Mips64EL =
       (Config->EMachine == EM_MIPS && Config->EKind == ELF64LEKind);
 
   // Add entry symbol. Note that AMDGPU binaries have no entry points.
   if (Config->Entry.empty() && !Config->Shared && !Config->Relocatable &&
       Config->EMachine != EM_AMDGPU)
     Config->Entry = (Config->EMachine == EM_MIPS) ? "__start" : "_start";
 

lld/trunk/test/ELF/emulation.s

 # X86-64-NEXT:   HeaderSize: 64
 # X86-64-NEXT:   ProgramHeaderEntrySize: 56
 # X86-64-NEXT:   ProgramHeaderCount:
 # X86-64-NEXT:   SectionHeaderEntrySize: 64
 # X86-64-NEXT:   SectionHeaderCount:
 # X86-64-NEXT:   StringTableSectionIndex:
 # X86-64-NEXT: }
 
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux-gnux32 %s -o %tx32
+# RUN: ld.lld -m elf32_x86_64 %tx32 -o %t2x32
+# RUN: llvm-readobj -file-headers %t2x32 | FileCheck --check-prefix=X32 %s
+# RUN: ld.lld %tx32 -o %t3x32
+# RUN: llvm-readobj -file-headers %t3x32 | FileCheck --check-prefix=X32 %s
+# X32:      ElfHeader {
+# X32-NEXT:   Ident {
+# X32-NEXT:     Magic: (7F 45 4C 46)
+# X32-NEXT:     Class: 32-bit (0x1)
+# X32-NEXT:     DataEncoding: LittleEndian (0x1)
+# X32-NEXT:     FileVersion: 1
+# X32-NEXT:     OS/ABI: SystemV (0x0)
+# X32-NEXT:     ABIVersion: 0
+# X32-NEXT:     Unused: (00 00 00 00 00 00 00)
+# X32-NEXT:   }
+# X32-NEXT:   Type: Executable (0x2)
+# X32-NEXT:   Machine: EM_X86_64 (0x3E)
+# X32-NEXT:   Version: 1
+# X32-NEXT:   Entry:
+# X32-NEXT:   ProgramHeaderOffset: 0x34
+# X32-NEXT:   SectionHeaderOffset:
+# X32-NEXT:   Flags [ (0x0)
+# X32-NEXT:   ]
+# X32-NEXT:   HeaderSize: 52
+# X32-NEXT:   ProgramHeaderEntrySize: 32
+# X32-NEXT:   ProgramHeaderCount:
+# X32-NEXT:   SectionHeaderEntrySize: 40
+# X32-NEXT:   SectionHeaderCount:
+# X32-NEXT:   StringTableSectionIndex:
+# X32-NEXT: }
+
 # RUN: llvm-mc -filetype=obj -triple=i686-unknown-linux %s -o %tx86
 # RUN: ld.lld -m elf_i386 %tx86 -o %t2x86
 # RUN: llvm-readobj -file-headers %t2x86 | FileCheck --check-prefix=X86 %s
 # RUN: ld.lld %tx86 -o %t3x86
 # RUN: llvm-readobj -file-headers %t3x86 | FileCheck --check-prefix=X86 %s
 # X86:      ElfHeader {
 # X86-NEXT:   Ident {
 # X86-NEXT:     Magic: (7F 45 4C 46)

lld/trunk/test/ELF/x86-64-rela.s

+// REQUIRES: x86
+// RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o
+// RUN: ld.lld %t.o -o %t.so -shared
+// RUN: llvm-readobj -dynamic-table %t.so | FileCheck %s
+// RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux-gnux32 %s -o %t.o
+// RUN: ld.lld %t.o -o %t.so -shared
+// RUN: llvm-readobj -dynamic-table %t.so | FileCheck %s
+
+        call foo@plt
+
+// CHECK:  0x{{0+}}14 PLTREL{{ +}}RELA