Revised "Don't return (null) from bfd_elf_sym_name"

Commit 68bbe1183379 results in a lot of follow up work, much of which
likely is still to be done. (And yes, since this is all for corrupted
or fuzzed object files, a whole lot of work doesn't much benefit
anyone.  It was a bad idea to put NULL in asymbol->name.)  So I'm
changing the approach to instead put a unique empty string for symbols
with a corrupted st_name.  An empty string won't require much work to
ensure nm, objcopy, objdump etc. won't crash, since these tools
already must work with unnamed local symbols.

The unique empty string is called bfd_symbol_error_name.  This patch
uses that name string for corrupted symbols in the ELF and COFF
backends.  Such symbols are displayed by nm and objdump as the
translated string "<corrupt>", which is what the COFF backend used to
put directly into corrupted symbols.

ie. it's the way I should have written the original patch, plus a few
tides and cleanups I retained from the reverted patches.

1 files changed, 10 insertions, 2 deletions

diff --git a/bfd/syms.c b/bfd/syms.c
index b370a33..68f0730 100644
--- a/bfd/syms.c
+++ b/bfd/syms.c
@@ -342,6 +342,11 @@ EXTERNAL
 .  const char *stab_name;	{* String for stab type.  *}
 .} symbol_info;
 .
+.{* An empty string that will not match the address of any other
+.   symbol name, even unnamed local symbols which will also have empty
+.   string names.  This can be used to flag a symbol as corrupt if its
+.   name uses an out of range string table index.  *}
+.extern const char bfd_symbol_error_name[];
 */
 
 #include "sysdep.h"
@@ -351,6 +356,8 @@ EXTERNAL
 #include "bfdlink.h"
 #include "aout/stab_gnu.h"
 
+const char bfd_symbol_error_name[] = { 0 };
+
 /*
 DOCDD
 INODE
@@ -394,7 +401,7 @@ bfd_is_local_label (bfd *abfd, asymbol *sym)
      if we didn't reject them here.  */
   if ((sym->flags & (BSF_GLOBAL | BSF_WEAK | BSF_FILE | BSF_SECTION_SYM)) != 0)
     return false;
-  if (sym->name == NULL)
+  if (sym->name == NULL || sym->name == bfd_symbol_error_name)
     return false;
   return bfd_is_local_label_name (abfd, sym->name);
 }
@@ -777,7 +784,8 @@ bfd_symbol_info (asymbol *symbol, symbol_info *ret)
   else
     ret->value = symbol->value + symbol->section->vma;
 
-  ret->name = symbol->name;
+  ret->name = (symbol->name != bfd_symbol_error_name
+	       ? symbol->name : _("<corrupt>"));
 }
 
 /*