[LLD] [COFF] Handle .eh_frame$symbol as associative comdat for MinGW

[mstorsjo]

Summary

This matches how it is done for .xdata and .pdata already.

On i386, the symbol name in the section name suffix does not contain the extra underscore prefix.

This is one part of a fix for PR42217.

[rnk]

lgtm

COFF/InputFiles.cpp

void ObjFile::recordPrevailingSymbolForMingw(
   // of the section chunk we actually include instead of discarding it,
   // add the symbol to a map to allow using it for implicitly
   // associating .[px]data$<func> sections to it.
   int32_t SectionNumber = Sym.getSectionNumber();
   SectionChunk *SC = SparseChunks[SectionNumber];
   if (SC && SC->getOutputCharacteristics() & IMAGE_SCN_MEM_EXECUTE) {
     StringRef Name;
     COFFObj->getSymbolName(Sym, Name);
+    if (getMachineType() == I386)
+      Name.consume_front("_");
     PrevailingSectionMap[Name] = SectionNumber;
   }
 }
 
 void ObjFile::maybeAssociateSEHForMingw(
     COFFSymbolRef Sym, const coff_aux_section_definition *Def,
     const DenseMap<StringRef, uint32_t> &PrevailingSectionMap) {
   StringRef Name;
   COFFObj->getSymbolName(Sym, Name);
-  if (Name.consume_front(".pdata$") || Name.consume_front(".xdata$")) {
-    // For MinGW, treat .[px]data$<func> as implicitly associative to
-    // the symbol <func>.
+  if (Name.consume_front(".pdata$") || Name.consume_front(".xdata$") ||
+      Name.consume_front(".eh_frame$")) {
+    // For MinGW, treat .[px]data$<func> and .eh_frame$<func> as implicitly
+    // associative to the symbol <func>.
     auto ParentSym = PrevailingSectionMap.find(Name);
     if (ParentSym != PrevailingSectionMap.end())
       readAssociativeDefinition(Sym, Def, ParentSym->second);
   }
 }
 
 Symbol *ObjFile::createRegular(COFFSymbolRef Sym) {
   SectionChunk *SC = SparseChunks[Sym.getSectionNumber()];

test/COFF/associative-comdat-mingw-i386.s

+# REQUIRES: x86
+
+# RUN: llvm-mc -triple=i686-windows-gnu %s -filetype=obj -o %t.obj
+
+# RUN: lld-link -lldmingw -entry:main %t.obj -out:%t.exe
+# RUN: llvm-objdump -s %t.exe | FileCheck %s
+
+# Check that the .eh_frame comdat was included, even if it had no symbols,
+# due to associativity with the symbol _foo.
+
+# CHECK: Contents of section .eh_fram:
+# CHECK:  403000 42
+
+        .text
+        .def            _main;
+        .scl            2;
+        .type           32;
+        .endef
+        .globl          _main
+        .p2align        4, 0x90
+_main:
+        call            _foo
+        ret
+
+        .section        .eh_frame$foo,"dr"
+        .linkonce       discard
+        .byte           0x42
+
+        .def            _foo;
+        .scl            2;
+        .type           32;
+        .endef
+        .section        .text$foo,"xr",discard,foo
+        .globl          _foo
+        .p2align        4
+_foo:
+        ret