[PATCH] D60306: Fix -emit-reloc against local symbols.

[Rui Ueyama via Phabricator via llvm-commits]

ruiu created this revision.
ruiu added reviewers: grimar, kees.
Herald added subscribers: MaskRay, arichardson, emaste.
Herald added a reviewer: espindola.
Herald added a project: LLVM.

Previously, we drop symbols starting with .L from the symbol table, so
if there is a relocation that refers a .L symbol, it ended up
referencing a null -- which happened to be interpreted as an absolute
symbol.

This patch copies all symbols including local ones if -emit-reloc is
given.

Fixes https://bugs.llvm.org/show_bug.cgi?id=41385


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D60306

Files:
  lld/ELF/Writer.cpp
  lld/test/ELF/emit-relocs-mergeable2.s


Index: lld/test/ELF/emit-relocs-mergeable2.s
===================================================================
--- /dev/null
+++ lld/test/ELF/emit-relocs-mergeable2.s
@@ -0,0 +1,15 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t.o
+# RUN: ld.lld --emit-relocs %t.o -o %t.exe
+# RUN: llvm-readelf --relocations %t.exe | FileCheck %s
+
+# CHECK: 0000000000201004  000000010000000b R_X86_64_32S 0000000000200120 .Lfoo + 8
+
+.globl  _start
+_start:
+  movq .Lfoo+8, %rax
+.section .rodata.cst16,"aM", at progbits,16
+.Lfoo:
+  .quad 0
+  .quad 0
+
Index: lld/ELF/Writer.cpp
===================================================================
--- lld/ELF/Writer.cpp
+++ lld/ELF/Writer.cpp
@@ -567,6 +567,11 @@
   if (Config->Discard == DiscardPolicy::None)
     return true;
 
+  // If -emit-reloc is given, all symbols including local ones need to be
+  // copied because they may be referenced by relocations.
+  if (Config->EmitRelocs)
+    return true;
+
   // In ELF assembly .L symbols are normally discarded by the assembler.
   // If the assembler fails to do so, the linker discards them if
   // * --discard-locals is used.


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