Re: [RFC] Collision between NT_GNU_BUILD_ATTRIBUTE_OPEN and NT_PPC_VMX

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Fri, Aug 11, 2017 at 3:43 PM, Gustavo Romero
<gromero@linux.vnet.ibm.com> wrote:
> Hi,
>
> After commit 9ef920e, "Add support for displaying and merging GNU_BUILD_NOTEs.",
> coredump file generated on PPC64 and displayed with 'binutils/readelf -n' shows
> errors in VMX/Altivec registers note section like:
>
>   readelf: Error: unrecognised attribute type in name field: 76
> <unknown name type>  0x00000220 NT_PPC_VMX (ppc Altivec registers)
> readelf: Error:     <invalid description size: 220>
>     <invalid descsz>
>
> Before it was:
>
> LINUX                0x00000220 NT_PPC_VMX (ppc Altivec registers)
>
> because NT_GNU_BUILD_ATTRIBUTE_OPEN (introduced by the aforementioned commit)
> has the same value as NT_PPC_VMX:
>
> $ grep 0x100 include/elf/common.h
> #define NT_PPC_VMX      0x100           /* PowerPC Altivec/VMX registers */
> #define NT_GNU_BUILD_ATTRIBUTE_OPEN     0x100
>
> If my understanding is correct about GNU_BUILD_NOTEs, it's just useful on
> run-time or dynamic / static linking and will never be present in a coredump
> file. If that holds I suggest the following simple fix:
>
> @@ -17477,8 +17503,8 @@ process_note (Elf_Internal_Note *  pnote,
>
>    printf ("  ");
>
> -  if (pnote->type == NT_GNU_BUILD_ATTRIBUTE_OPEN
> -      || pnote->type == NT_GNU_BUILD_ATTRIBUTE_FUNC)
> +  if (elf_header.e_type != ET_CORE && (pnote->type == NT_GNU_BUILD_ATTRIBUTE_OPEN
> +      || pnote->type == NT_GNU_BUILD_ATTRIBUTE_FUNC))
>      print_gnu_build_attribute_name (pnote);
>    else
>      print_symbol (-20, name);
> @@ -17496,8 +17522,8 @@ process_note (Elf_Internal_Note *  pnote,
>      return print_stapsdt_note (pnote);
>    else if (const_strneq (pnote->namedata, "CORE"))
>      return print_core_note (pnote);
> -  else if (pnote->type == NT_GNU_BUILD_ATTRIBUTE_OPEN
> -          || pnote->type == NT_GNU_BUILD_ATTRIBUTE_FUNC)
> +  else if (elf_header.e_type != ET_CORE && (pnote->type == NT_GNU_BUILD_ATTRIBUTE_OPEN
> +          || pnote->type == NT_GNU_BUILD_ATTRIBUTE_FUNC))
>      return print_gnu_build_attribute_description (pnote, file);
>
> If that change is upvoted I'll send a formal patch for review.
>
> Thank you.
>

This is wrong.  pnote->type is unique only for a given pnote->namedata.
 NT_GNU_* should be be checked for "GNU" notes.


-- 
H.J.