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[MC] - Add .stack_size sections into groups and link them with .text

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D39788 added a '.stack-size' section containing metadata on function stack sizes
to output ELF files behind the new -stack-size-section flag.

This change does following two things on top:

1) Imagine the case when there are -ffunction-sections flag given and there are text sections in COMDATs. 
    The patch adds a '.stack-size' section into corresponding COMDAT group, so that linker will be able to
    eliminate them fast during resolving the COMDATs.
2) Patch sets a SHF_LINK_ORDER flag and links '.stack-size' with the corresponding .text.
   With that linker will be able to do -gc-sections on dead stack sizes sections.

Differential revision: https://reviews.llvm.org/D46874

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@335332 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
George Rimar
2018-06-22 10:10:53 +00:00
parent 9104c92c0b
commit 08d6b0d9f0
7 changed files with 77 additions and 9 deletions
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lib/MC/MCObjectFileInfo.cpp
+21
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@@ -948,3 +948,24 @@ MCSection *MCObjectFileInfo::getDwarfTypesSection(uint64_t Hash) const {
return Ctx->getELFSection(".debug_types", ELF::SHT_PROGBITS, ELF::SHF_GROUP,
0, utostr(Hash));
}
MCSection *
MCObjectFileInfo::getStackSizesSection(const MCSection &TextSec) const {
if (Env != IsELF)
return StackSizesSection;
const MCSectionELF &ElfSec = static_cast<const MCSectionELF &>(TextSec);
unsigned Flags = ELF::SHF_LINK_ORDER;
StringRef GroupName;
if (const MCSymbol *Group = ElfSec.getGroup()) {
GroupName = Group->getName();
Flags |= ELF::SHF_GROUP;
}
const MCSymbol *Link = TextSec.getBeginSymbol();
auto It = StackSizesUniquing.insert({Link, StackSizesUniquing.size()});
unsigned UniqueID = It.first->second;
return Ctx->getELFSection(".stack_sizes", ELF::SHT_PROGBITS, Flags, 0,
GroupName, UniqueID, cast<MCSymbolELF>(Link));
}