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Changes to support TLS access emitted in ILC (x64 win/linux) #429

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merged 2 commits into from
Jun 15, 2023
Merged

Changes to support TLS access emitted in ILC (x64 win/linux) #429

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da38b29
tls support
VSadov Jun 8, 2023
36ce724
more operators
VSadov Jun 9, 2023
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2 changes: 1 addition & 1 deletion llvm/include/llvm/MC/MCObjectFileInfo.h
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Original file line number Diff line number Diff line change
Expand Up @@ -344,7 +344,7 @@ class MCObjectFileInfo {
}

MCSection *getTLSExtraDataSection() const { return TLSExtraDataSection; }
const MCSection *getTLSDataSection() const { return TLSDataSection; }
MCSection *getTLSDataSection() const { return TLSDataSection; }
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Why is this needed? Could we just mark things const on the objwriter side? Changes to LLVM outside of tools/objwriter need to be ported every time we update LLVM so there's a lot of value in keeping them as minimal as possible.

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Could we just mark things const on the objwriter side

I tried and propagating the const requires a lot of changes (const can be viral).
It is also inconsistent with the treatment other section accessors - i.e why getTLSDataSection is a const and getTLSBSSSection isn't?

I think the difference is unintentional. If we want const, we should make other sections accessors const as well.

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@VSadov VSadov Jun 14, 2023 •
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One possibility is to keep getTLSDataSection() as const (for no reason) and just cast the const away in the object writer.

There is a danger that something may eventually make dependency on this being const and it would not be easily noticeable when updating.

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cast the const away in the object writer

Such workaround stands out in the code and feels like a mildly dangerous hack.
I think we can do such change if removing the const becomes a burden when updating. It probably won't if upstream code does not change. It does not look like this part changes often.

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Just to be sure - I have noted the concern, but any way to deal with this issue has a downside. Removing the 'const' seems not distinctly worse than other solutions.
We need to pick one way to move forward while decision is not binding, since it is an implementation detail that can be changed. I am going to merge what we have, but will keep an eye if this becomes an issue.

MCSection *getTLSBSSSection() const { return TLSBSSSection; }

MCSection *getStackMapSection() const { return StackMapSection; }
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16 changes: 16 additions & 0 deletions llvm/tools/objwriter/objwriter.cpp
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Expand Up @@ -222,6 +222,10 @@ MCSection *ObjectWriter::GetSection(const char *SectionName,
Section = ObjFileInfo->getReadOnlySection();
} else if (strcmp(SectionName, "xdata") == 0) {
Section = ObjFileInfo->getXDataSection();
} else if (strcmp(SectionName, "tdata") == 0) {
Section = ObjFileInfo->getTLSDataSection();
} else if (strcmp(SectionName, "tbss") == 0) {
Section = ObjFileInfo->getTLSBSSSection();
} else if (strcmp(SectionName, "bss") == 0) {
if (OutContext->getObjectFileType() == MCContext::IsMachO) {
Section = ObjFileInfo->getDataBSSSection();
Expand Down Expand Up @@ -457,6 +461,18 @@ int ObjectWriter::EmitSymbolRef(const char *SymbolName,
case RelocType::IMAGE_REL_BASED_DIR64:
Size = 8;
break;
case RelocType::IMAGE_REL_SECREL:
Kind = MCSymbolRefExpr::VK_SECREL;
Size = 4;
break;
case RelocType::IMAGE_REL_TLSGD:
Kind = MCSymbolRefExpr::VK_TLSGD;
Size = 4;
break;
case RelocType::IMAGE_REL_TPOFF:
Kind = MCSymbolRefExpr::VK_TPOFF;
Size = 4;
break;
case RelocType::IMAGE_REL_BASED_REL32:
if (OutContext->getObjectFileType() == MCContext::IsMachO &&
OutContext->getTargetTriple().getArch() == Triple::aarch64) {
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3 changes: 3 additions & 0 deletions llvm/tools/objwriter/objwriter.h
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Expand Up @@ -59,6 +59,9 @@ enum class RelocType {
IMAGE_REL_BASED_RELPTR32 = 0x7C,
IMAGE_REL_BASED_ARM64_PAGEBASE_REL21 = 0x81,
IMAGE_REL_BASED_ARM64_PAGEOFFSET_12A = 0x82,
IMAGE_REL_SECREL = 0x104,
IMAGE_REL_TLSGD = 0x105,
IMAGE_REL_TPOFF = 0x106,
};

enum class SymbolRefFlags
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