[LLD] [COFF] Strip section name suffix from mingw comdats

[mstorsjo]

Summary

This is one part of the fix for PR42217.

Not sure where the best place to put the stripping of the section name suffix. I fear (maybe needlessly?) that it breaks something else if we'd place the logic e.g. somewhere in the Chunk classes.

[rnk]

lgtm

I don't think we can do it earlier, I think this is the right spot to do this. It will cut down on memory usage as well, by the way, since we'll have fewer single Chunk PartialSection objects on mingw.

COFF/Writer.cpp

800 ↗

(On Diff #204825)

Please add a comment explaining that, on mingw, comdat groups are formed by putting the comdat group name after the $ in the section name. This code ignores the comdat group name for the purpose of section sorting.

lld/trunk/COFF/Writer.cpp

void Writer::createSections() {
   // Then bin chunks by name and output characteristics.
   for (Chunk *C : Symtab->getChunks()) {
     auto *SC = dyn_cast<SectionChunk>(C);
     if (SC && !SC->Live) {
       if (Config->Verbose)
         SC->printDiscardedMessage();
       continue;
     }
-    PartialSection *PSec = createPartialSection(C->getSectionName(),
+    StringRef Name = C->getSectionName();
+    // On MinGW, comdat groups are formed by putting the comdat group name
+    // after the '$' in the section name. Such a section name suffix shouldn't
+    // imply separate alphabetical sorting of those section chunks though.
+    if (Config->MinGW && SC && SC->isCOMDAT())
+      Name = Name.split('$').first;
+    PartialSection *PSec = createPartialSection(Name,
                                                 C->getOutputCharacteristics());
     PSec->Chunks.push_back(C);
   }
 
   // Even in non MinGW cases, we might need to link against GNU import
   // libraries.
   bool HasIdata = fixGnuImportChunks();
   if (!Idata.empty())

lld/trunk/test/COFF/eh_frame_suffix_sorting.s

+# REQUIRES: x86
+
+# RUN: llvm-mc -triple=i686-windows-gnu %s -filetype=obj -o %t.main.o
+# RUN: llvm-mc -filetype=obj -triple=i686-windows-gnu \
+# RUN:   %p/Inputs/eh_frame_terminator-crtend.s -o %t.crtend.o
+
+# RUN: lld-link -lldmingw -entry:main %t.main.o %t.crtend.o -out:%t.exe
+# RUN: llvm-objdump -s %t.exe | FileCheck %s
+
+# Check that the contents of .eh_frame$foo was placed before .eh_frame from
+# crtend.o, even if the former had a section name suffix.
+
+# CHECK: Contents of section .eh_fram:
+# CHECK:  403000 4203
+
+        .text
+        .def            _main;
+        .scl            2;
+        .type           32;
+        .endef
+        .globl          _main
+        .p2align        4, 0x90
+_main:
+        call            _foo
+        ret
+
+        .section        .eh_frame$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