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

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.

Differential Revision: https://reviews.llvm.org/D63350

llvm-svn: 363456

Author: mstorsjo

lld/COFF/InputFiles.cpp

@@ -288,6 +288,8 @@ void ObjFile::recordPrevailingSymbolForMingw(
   if (SC && SC->getOutputCharacteristics() & IMAGE_SCN_MEM_EXECUTE) {
     StringRef Name;
     COFFObj->getSymbolName(Sym, Name);
+    if (getMachineType() == I386)
+      Name.consume_front("_");
     PrevailingSectionMap[Name] = SectionNumber;
   }
 }
@@ -297,9 +299,10 @@ void ObjFile::maybeAssociateSEHForMingw(
     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);

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

@@ -0,0 +1,37 @@
+# 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