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

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

llvm-svn: 335332

1 files changed, 21 insertions, 0 deletions

diff --git a/llvm/lib/MC/MCObjectFileInfo.cpp b/llvm/lib/MC/MCObjectFileInfo.cpp
index b075f22..2b5c9c7 100644
--- a/llvm/lib/MC/MCObjectFileInfo.cpp
+++ b/llvm/lib/MC/MCObjectFileInfo.cpp
@@ -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));
+}