[PATCH] D54624: [LLD][ELF] Error if _GLOBAL_OFFSET_TABLE_ is defined in input objects

[Peter Smith via Phabricator via llvm-commits]

peter.smith updated this revision to Diff 175677.
peter.smith added a comment.

Thanks for the comment. I've made the suggested change.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D54624/new/

https://reviews.llvm.org/D54624

Files:
  ELF/Writer.cpp
  test/ELF/global-offset-table-position-redef-err.s


Index: test/ELF/global-offset-table-position-redef-err.s
===================================================================
--- /dev/null
+++ test/ELF/global-offset-table-position-redef-err.s
@@ -0,0 +1,14 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o
+# RUN: not ld.lld -shared %t.o -o %t.so 2>&1 | FileCheck %s
+
+# On some targets the location of the _GLOBAL_OFFSET_TABLE_ symbol table can
+# matter for the correctness of some relocations. Follow the example of ld.gold
+# and give a multiple definition error if input objects attempt to redefine it.
+
+# CHECK: ld.lld: error: {{.*o}} cannot redefine linker defined symbol '_GLOBAL_OFFSET_TABLE_'
+
+.data
+.global _GLOBAL_OFFSET_TABLE_
+_GLOBAL_OFFSET_TABLE_:
+.word 0
Index: ELF/Writer.cpp
===================================================================
--- ELF/Writer.cpp
+++ ELF/Writer.cpp
@@ -212,9 +212,20 @@
   // _GLOBAL_OFFSET_TABLE_ and _SDA_BASE_ from the 32-bit ABI. It is used to
   // represent the TOC base which is offset by 0x8000 bytes from the start of
   // the .got section.
-  ElfSym::GlobalOffsetTable = addOptionalRegular(
-      (Config->EMachine == EM_PPC64) ? ".TOC." : "_GLOBAL_OFFSET_TABLE_",
-      Out::ElfHeader, Target->GotBaseSymOff);
+  // We do not allow _GLOBAL_OFFSET_TABLE_ to be defined by input objects as the
+  // correctness of some relocations depends on its value.
+  StringRef GotTableSymName =
+      (Config->EMachine == EM_PPC64) ? ".TOC." : "_GLOBAL_OFFSET_TABLE_";
+  if (Symbol *S = Symtab->find(GotTableSymName)) {
+    if (S->isDefined())
+      error(toString(S->File) + " cannot redefine linker defined symbol '" +
+            GotTableSymName + "'");
+    else
+      ElfSym::GlobalOffsetTable = Symtab->addDefined(
+          GotTableSymName, STV_HIDDEN, STT_NOTYPE, Target->GotBaseSymOff,
+          /*Size=*/0, STB_GLOBAL, Out::ElfHeader,
+          /*File=*/nullptr);
+  }
 
   // __ehdr_start is the location of ELF file headers. Note that we define
   // this symbol unconditionally even when using a linker script, which


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