[PATCH] D78820: [LLD][ELF] Eliminate symbols of merged .ARM.exidx sections.

[Igor Kudrin via Phabricator via llvm-commits]

ikudrin updated this revision to Diff 260246.
ikudrin added a comment.

- Reworked the patch so that the local symbols for `.ARM.exidx` sections are not added to the symbols table. Thanks for the suggestion, @psmith!


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D78820/new/

https://reviews.llvm.org/D78820

Files:
  lld/ELF/Writer.cpp
  lld/test/ELF/arm-exidx-mapping-symbols.s


Index: lld/test/ELF/arm-exidx-mapping-symbols.s
===================================================================
--- /dev/null
+++ lld/test/ELF/arm-exidx-mapping-symbols.s
@@ -0,0 +1,27 @@
+// REQUIRES: arm
+// Test that symbols which point to input .ARM.exidx sections are eliminated.
+// These symbols might be produced, for example, by GNU tools.
+
+// RUN: llvm-mc -filetype=obj -triple=armv7a-none-linux-gnueabi %s -o %t
+// RUN: ld.lld %t -o %t2
+// RUN: llvm-readelf -s %t2 | FileCheck %s
+
+// CHECK-NOT: $d.exidx.foo
+
+    .syntax unified
+    .section .text.foo,"axG",%progbits,foo,comdat
+foo:
+    bx lr
+
+// GNU as adds mapping symbols "$d" for .ARM.exidx sections it generates.
+// llvm-mc does not do that, so reproduce that manually.
+    .section .ARM.exidx.text.foo,"ao?",%0x70000001,.text.foo
+$d.exidx.foo:
+    .reloc 0, R_ARM_NONE, __aeabi_unwind_cpp_pr0
+    .long .text.foo(PREL31)
+    .long 0x80b0b0b0
+
+    .section .text.h
+    .global __aeabi_unwind_cpp_pr0
+__aeabi_unwind_cpp_pr0:
+    bx lr
Index: lld/ELF/Writer.cpp
===================================================================
--- lld/ELF/Writer.cpp
+++ lld/ELF/Writer.cpp
@@ -681,6 +681,15 @@
   if (config->copyRelocs && sym.used)
     return true;
 
+  // Exclude local symbols pointing to .ARM.exidx sections.
+  // They are probably mapping symbols "$d", which are optional for these
+  // sections. After merging the .ARM.exidx sections, some of these symbols
+  // may become dangling. The easiest way to avoid the issue is not to add
+  // them to the symbol table from the beginning.
+  if (config->emachine == EM_ARM && sym.section &&
+      sym.section->type == SHT_ARM_EXIDX)
+    return false;
+
   if (config->discard == DiscardPolicy::None)
     return true;
   if (config->discard == DiscardPolicy::All)


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