[PATCH] D41657: Do not look up symbol names when n_strx == 0

[Michael Trent via Phabricator via llvm-commits]

mtrent created this revision.
mtrent added a reviewer: enderby.
Herald added a subscriber: JDevlieghere.

Historical tools for working with mach-o binaries verify the nlist field
n_strx has a non-zero value before using that value to retrieve symbol names.
Under some cirumstances, llvm-nm will attempt to display the symbol name at 
position 0, even though symbol names at that position are not well defined. 
This change addresses this problem by returning an empty string when n_strx
is zero.

rdar://problem/35750548


https://reviews.llvm.org/D41657

Files:
  lib/Object/MachOObjectFile.cpp
  test/tools/llvm-nm/X86/Inputs/macho-dwarf-x86_64
  test/tools/llvm-nm/X86/macho-dwarf.test


Index: test/tools/llvm-nm/X86/macho-dwarf.test
===================================================================
--- /dev/null
+++ test/tools/llvm-nm/X86/macho-dwarf.test
@@ -0,0 +1,5 @@
+# RUN: llvm-nm -ap %p/Inputs/macho-dwarf-x86_64 | cat -e | FileCheck %s
+
+# CHECK-NOT: ENSYM  $
+# CHECK: ENSYM $
+
Index: lib/Object/MachOObjectFile.cpp
===================================================================
--- lib/Object/MachOObjectFile.cpp
+++ lib/Object/MachOObjectFile.cpp
@@ -1659,6 +1659,10 @@
 Expected<StringRef> MachOObjectFile::getSymbolName(DataRefImpl Symb) const {
   StringRef StringTable = getStringTableData();
   MachO::nlist_base Entry = getSymbolTableEntryBase(*this, Symb);
+  if (Entry.n_strx == 0) {
+    // contents of the StringTable at n_strx 0 are not defined
+    return StringRef();
+  }
   const char *Start = &StringTable.data()[Entry.n_strx];
   if (Start < getData().begin() || Start >= getData().end()) {
     return malformedError("bad string index: " + Twine(Entry.n_strx) +


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