release/18.x: [LLD] [COFF] Don't add pseudo relocs for dangling references (#88487)

[llvmbot]

Backport 9c970d5

Requested by: @mstorsjo

[llvmbot]

@cjacek What do you think about merging this PR to the release branch?

[llvmbot]

@llvm/pr-subscribers-lld-coff

@llvm/pr-subscribers-lld

Author: None (llvmbot)

Changes

Backport 9c970d5

Requested by: @mstorsjo

---

Full diff: https://github.com/llvm/llvm-project/pull/88759.diff

2 Files Affected:

• (modified) lld/COFF/Chunks.cpp (+7)
• (added) lld/test/COFF/autoimport-gc.s (+41)

diff --git a/lld/COFF/Chunks.cpp b/lld/COFF/Chunks.cpp
index 39f4575031be54..e2074932bc466e 100644
--- a/lld/COFF/Chunks.cpp
+++ b/lld/COFF/Chunks.cpp
@@ -652,6 +652,13 @@ void SectionChunk::getRuntimePseudoRelocs(
         dyn_cast_or_null<Defined>(file->getSymbol(rel.SymbolTableIndex));
     if (!target || !target->isRuntimePseudoReloc)
       continue;
+    // If the target doesn't have a chunk allocated, it may be a
+    // DefinedImportData symbol which ended up unnecessary after GC.
+    // Normally we wouldn't eliminate section chunks that are referenced, but
+    // references within DWARF sections don't count for keeping section chunks
+    // alive. Thus such dangling references in DWARF sections are expected.
+    if (!target->getChunk())
+      continue;
     int sizeInBits =
         getRuntimePseudoRelocSize(rel.Type, file->ctx.config.machine);
     if (sizeInBits == 0) {
diff --git a/lld/test/COFF/autoimport-gc.s b/lld/test/COFF/autoimport-gc.s
new file mode 100644
index 00000000000000..fef6c02eba82f9
--- /dev/null
+++ b/lld/test/COFF/autoimport-gc.s
@@ -0,0 +1,41 @@
+# REQUIRES: x86
+# RUN: split-file %s %t.dir
+
+# RUN: llvm-mc -triple=x86_64-windows-gnu %t.dir/lib.s -filetype=obj -o %t.dir/lib.obj
+# RUN: lld-link -out:%t.dir/lib.dll -dll -entry:DllMainCRTStartup %t.dir/lib.obj -lldmingw -implib:%t.dir/lib.lib
+
+# RUN: llvm-mc -triple=x86_64-windows-gnu %t.dir/main.s -filetype=obj -o %t.dir/main.obj
+# RUN: lld-link -lldmingw -out:%t.dir/main.exe -entry:main %t.dir/main.obj %t.dir/lib.lib -opt:ref -debug:dwarf
+
+#--- main.s
+    .global main
+    .section .text$main,"xr",one_only,main
+main:
+    ret
+
+    .global other
+    .section .text$other,"xr",one_only,other
+other:
+    movq .refptr.variable(%rip), %rax
+    movl (%rax), %eax
+    ret
+
+    .section .rdata$.refptr.variable,"dr",discard,.refptr.variable
+    .global .refptr.variable
+.refptr.variable:
+    .quad   variable
+
+    .section .debug_info
+    .long 1
+    .quad variable
+    .long 2
+
+#--- lib.s
+    .global variable
+    .global DllMainCRTStartup
+    .text
+DllMainCRTStartup:
+    ret
+    .data
+variable:
+    .long 42

[tstellar]

Hi @mstorsjo (or anyone else). If you would like to add a note about this fix in the release notes (completely optional). Please reply to this comment with a one or two sentence description of the fix.