.gcc_except_table: Set SHF_LINK_ORDER if binutils>=2.36, and drop unneeded unique ID for -fno-unique-section-names

GNU ld>=2.36 supports mixed SHF_LINK_ORDER and non-SHF_LINK_ORDER sections in an
output section, so we can set SHF_LINK_ORDER if -fbinutils-version=2.36 or above.

If -fno-function-sections or older binutils, drop unique ID for -fno-unique-section-names.
The users can just specify -fbinutils-version=2.36 or above to allow GC with both GNU ld and LLD.
(LLD does not support garbage collection of non-group non-SHF_LINK_ORDER .gcc_except_table sections.)

1 files changed, 15 insertions, 20 deletions

diff --git a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
index fe64b38..cccac07 100644
--- a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
+++ b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
@@ -834,9 +834,8 @@ MCSection *TargetLoweringObjectFileELF::getSectionForJumpTable(
                                    /* AssociatedSymbol */ nullptr);
 }
 
-MCSection *
-TargetLoweringObjectFileELF::getSectionForLSDA(const Function &F,
-                                               const TargetMachine &TM) const {
+MCSection *TargetLoweringObjectFileELF::getSectionForLSDA(
+    const Function &F, const MCSymbol &FnSym, const TargetMachine &TM) const {
   // If neither COMDAT nor function sections, use the monolithic LSDA section.
   // Re-use this path if LSDASection is null as in the Arm EHABI.
   if (!LSDASection || (!F.hasComdat() && !TM.getFunctionSections()))
@@ -845,30 +844,26 @@ TargetLoweringObjectFileELF::getSectionForLSDA(const Function &F,
   const auto *LSDA = cast<MCSectionELF>(LSDASection);
   unsigned Flags = LSDA->getFlags();
   StringRef Group;
+  const MCSymbolELF *LinkedToSym = nullptr;
   if (F.hasComdat()) {
     Group = F.getComdat()->getName();
     Flags |= ELF::SHF_GROUP;
   }
+  // Use SHF_LINK_ORDER to facilitate --gc-sections if we can use GNU ld>=2.36
+  // or LLD, which support mixed SHF_LINK_ORDER & non-SHF_LINK_ORDER.
+  if (TM.getFunctionSections() &&
+      (getContext().getAsmInfo()->useIntegratedAssembler() &&
+       getContext().getAsmInfo()->binutilsIsAtLeast(2, 36))) {
+    Flags |= ELF::SHF_LINK_ORDER;
+    LinkedToSym = cast<MCSymbolELF>(&FnSym);
+  }
 
   // Append the function name as the suffix like GCC, assuming
   // -funique-section-names applies to .gcc_except_table sections.
-  if (TM.getUniqueSectionNames())
-    return getContext().getELFSection(LSDA->getName() + "." + F.getName(),
-                                      LSDA->getType(), Flags, 0, Group,
-                                      MCSection::NonUniqueID, nullptr);
-
-  // Allocate a unique ID if function sections && (integrated assembler or GNU
-  // as>=2.35). Note we could use SHF_LINK_ORDER to facilitate --gc-sections but
-  // that would require that we know the linker is a modern LLD (12.0 or later).
-  // GNU ld as of 2.35 does not support mixed SHF_LINK_ORDER &
-  // non-SHF_LINK_ORDER components in an output section
-  // https://sourceware.org/bugzilla/show_bug.cgi?id=26256
-  unsigned ID = TM.getFunctionSections() &&
-                        getContext().getAsmInfo()->useIntegratedAssembler()
-                    ? NextUniqueID++
-                    : MCSection::NonUniqueID;
-  return getContext().getELFSection(LSDA->getName(), LSDA->getType(), Flags, 0,
-                                    Group, ID, nullptr);
+  return getContext().getELFSection(
+      (TM.getUniqueSectionNames() ? LSDA->getName() + "." + F.getName()
+                                  : LSDA->getName()),
+      LSDA->getType(), Flags, 0, Group, MCSection::NonUniqueID, LinkedToSym);
 }
 
 bool TargetLoweringObjectFileELF::shouldPutJumpTableInFunctionSection(