Re: [PATCH v3 3/6] libdwelf: Add dwelf_dwarf_gnu_debugaltlink

[Florian Weimer <fweimer at redhat dot com>]

On 04/18/2014 01:02 PM, Mark Wielaard wrote:
> On Tue, 2014-04-15 at 14:49 +0200, Florian Weimer wrote:
>> +2014-04-15  Florian Weimer  <fweimer@redhat.com>
>> +
>> +	* dwelf_dwarf_gnu_debugaltlink.c: New file.
>> +	* Makefile.am (libdwelf_a_SOURCES): Add it.
>> +	* libdwelf.h (dwelf_dwarf_gnu_debugaltlink): Declare new function.
>> +	* libdwelfP.h (dwelf_dwarf_gnu_debugaltlink): Add internal
>> +	declaration.
>
> The code looks fine. But I still like the "tri-state" return more to
> indicate why/how things went. Precisely because then you don't have to
> do:
>
>> +  Elf_Data *data = dwarf->sectiondata[IDX_gnu_debugaltlink];
>> +  if (data == NULL)
>> +    {
>> +      /* Missing data is not actually an error. */
>> +      __libdw_seterrno (0);
>> +      return NULL;
>> +    }
>> [...]
>> +/* Returns the name of the alternate debug information file from the
>> +   .gnu_debugaltlink section if found in the ELF.  On success, writes
>> +   a pointer to the build ID to *BUILD_IDP, and its length to
>> +   *BUILD_ID_LENP.  Returns NULL if the ELF file didn't have a
>> +   .gnu_debuglink section (and sets the dwarf_errcode error code to
>> +   0), had malformed data in the section or some other error occured.
>> +   The returned pointers are valid while the ELF handle is valid.  */
>> +extern const char *dwelf_dwarf_gnu_debugaltlink (Dwarf *dwarf,
>> +						 const void **build_idp,
>> +						 size_t *build_id_lenp);

I'm not sure if this addresses this completely addresses the issue.  A 
return value of 0 could mean "no debugaltlink data" or "the build ID has 
zero length".

I don't like setting the error code to zero, but as far as I can tell, 
the error codes are not exposed, and a caller would have to resort to 
string comparisons to check if it's the expected "missing section" 
error, or something about lack of resources or malformed input data.

>> +2014-04-15  Florian Weimer  <fweimer@redhat.com>
>> +
>> +	* debugaltlink.c, run-debugaltlink.sh: New files.
>> +	* Makefile.am (check_PROGRAMS): Add debugaltlink.
>> +	(TESTS): Add run-debugaltlink.sh.
>> +	(debugaltlink_LDADD): New variable.
>
> Thanks for adding the testcase. run-debugaltlink.sh should also be added
> to EXTRA_DIST (I also forgot that in my dwelf_elf_gnu_debuglink patch
> (fixed on the mjw/dwelf branch).

Can't we handle this in a better way with make variables, so that the 
file needs to be listed in just one place?

Anyway, I've fixed it in my copy.

-- 
Florian Weimer / Red Hat Product Security Team