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[X86][MC] Support R_X86_64_CODE_4_GOTPC32_TLSDESC #116908

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Merged
merged 3 commits into from
Nov 22, 2024
Merged

[X86][MC] Support R_X86_64_CODE_4_GOTPC32_TLSDESC #116908

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a4f65f2
[X86][MC] Support R_X86_64_CODE_4_GOTPC32_TLSDESC
fzou1 Nov 15, 2024
a45ba4f
Added trailing '\n'.
fzou1 Nov 20, 2024
b2adcd5
Address comments.
fzou1 Nov 21, 2024
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1 change: 1 addition & 0 deletions llvm/include/llvm/BinaryFormat/ELFRelocs/x86_64.def
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Expand Up @@ -45,3 +45,4 @@ ELF_RELOC(R_X86_64_GOTPCRELX, 41)
ELF_RELOC(R_X86_64_REX_GOTPCRELX, 42)
ELF_RELOC(R_X86_64_CODE_4_GOTPCRELX, 43)
ELF_RELOC(R_X86_64_CODE_4_GOTTPOFF, 44)
ELF_RELOC(R_X86_64_CODE_4_GOTPC32_TLSDESC, 45)
4 changes: 3 additions & 1 deletion llvm/lib/Target/X86/MCTargetDesc/X86ELFObjectWriter.cpp
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Expand Up @@ -191,7 +191,9 @@ static unsigned getRelocType64(MCContext &Ctx, SMLoc Loc,
case MCSymbolRefExpr::VK_TLSCALL:
return ELF::R_X86_64_TLSDESC_CALL;
case MCSymbolRefExpr::VK_TLSDESC:
return ELF::R_X86_64_GOTPC32_TLSDESC;
return ((unsigned)Kind == X86::reloc_riprel_4byte_relax_rex2)
? ELF::R_X86_64_CODE_4_GOTPC32_TLSDESC
: ELF::R_X86_64_GOTPC32_TLSDESC;
case MCSymbolRefExpr::VK_TLSGD:
checkIs32(Ctx, Loc, Type);
return ELF::R_X86_64_TLSGD;
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1 change: 1 addition & 0 deletions llvm/lib/Target/X86/MCTargetDesc/X86MCCodeEmitter.cpp
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Expand Up @@ -666,6 +666,7 @@ void X86MCCodeEmitter::emitMemModRMByte(
case X86::SBB64rm:
case X86::SUB64rm:
case X86::XOR64rm:
case X86::LEA64r:
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We don't need LEA64r before REX2?

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Sorry. I don't understand. We need to check LEA64r with REX2 prefix and add R_X86_64_CODE_4_GOTPC32_TLSDESC relocation for it.

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My question is: Why we don't need to check LEA64r when REX prefix was added? Is LEA64r special to REX2?

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It's not special to REX2. Here we need to distinguish REX2 prefix and others and set corresponding relocation type (R_X86_64_CODE_4_GOTPC32_TLSDESC) if it's REX2 prefix. For REX prefix, we didn't have to distinguish it and others in the past.

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Got it.

return Kind == REX2 ? X86::reloc_riprel_4byte_relax_rex2
: Kind == REX ? X86::reloc_riprel_4byte_relax_rex
: X86::reloc_riprel_4byte_relax;
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12 changes: 12 additions & 0 deletions llvm/test/MC/X86/tlsdesc-64.s
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Expand Up @@ -17,3 +17,15 @@
leaq a@tlsdesc(%rip), %rax
call *a@tlscall(%rax)
addq %fs:0, %rax

# PRINT: leaq a@tlsdesc(%rip), %r16
# PRINT-NEXT: callq *a@tlscall(%r16)

# CHECK: 12: leaq (%rip), %r16 # 0x1a <{{.*}}>
# CHECK-NEXT: 0000000000000016: R_X86_64_CODE_4_GOTPC32_TLSDESC a-0x4
# CHECK-NEXT: 1a: callq *(%r16)
# CHECK-NEXT: 000000000000001a: R_X86_64_TLSDESC_CALL a
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Is R_X86_64_TLSDESC_CALL expected? Or we need to check R_X86_64_CODE_4_TLSDESC_CALL?

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Yes. R_X86_64_TLSDESC_CALL is expected. There is no R_X86_64_CODE_4_TLSDESC_CALL type. As I understand, we don't need to rewrite/change the instruction so we don't need to know how many bytes the instruction starts before relocation offset.


leaq a@tlsdesc(%rip), %r16
call *a@tlscall(%r16)
addq %fs:0, %r16
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