Re: Synthetic symbol leak in in elf_x86_64_get_synthetic_symtab and elf_read_minimal_symbols

[Yao Qi <qiyaoltc@gmail.com>]

On 17-08-07 10:19:15, Alex Lindsay wrote:
> 
> We perform a couple of  dynamic allocations in
> elf_x86_64_get_synthetic_symtab (elf64-x86-64.c):
> 
>   s = *ret = (asymbol *) bfd_zmalloc (size);
> 
>   names = (char *) bfd_malloc (size);
> 
> that appear to never get freed. My patch for this:

Good catch!  It is more complicated that other bfd targets allocate
memory for asymbol in a different way as if asymbol.name is defined
as an zero-length array, so memory allocated for both asymbol and .name
in one bfd_malloc call, like,

	  sym = *r->sym_ptr_ptr;
	  if (!sym_exists_at (syms, opdsymend, symcount,
			      sym->section->id, sym->value + r->addend))
	    {
	      ++count;
	      size += sizeof (asymbol);
	      size += strlen (syms[i]->name) + 2;
	    }
	}

      if (size == 0)
	goto done;
      s = *ret = bfd_malloc (size);

or

  size = count * sizeof (asymbol);
  p = relplt->relocation;
  for (i = 0; i < count; i++, p += elf32_arm_size_info.int_rels_per_ext_rel)
    {
      size += strlen ((*p->sym_ptr_ptr)->name) + sizeof ("@plt");
      if (p->addend != 0)
	size += sizeof ("+0x") - 1 + 8;
    }

  s = *ret = (asymbol *) bfd_malloc (size);

> 
> diff --git a/gdb/elfread.c b/gdb/elfread.c
> index ece704ca7c..5ed8a6f957 100644
> --- a/gdb/elfread.c
> +++ b/gdb/elfread.c
> @@ -1144,6 +1144,9 @@ elf_read_minimal_symbols (struct objfile *objfile, int
> symfile_flags,
> 
>    if (symtab_create_debug)
>      fprintf_unfiltered (gdb_stdlog, "Done reading minimal symbols.\n");
> +  if (synthcount > 0)
> +    xfree ((char *) synthsyms->name);

We can't do this for some bfd targets.

> +  xfree (synthsyms);

We can only safely do this, but .name is leaked for x86_64.  Other
tools using bfd, like objdump, nm, and gprof may have this issue too.
I'll ask binutils people on asymbol allocation and de-allocation.

-- 
Yao (齐尧)