Re: [PATCH 2/2] perf symbols: debuglink should take symfs option into account

[Victor Kamensky]

David,

Thank you for response!

On 21 January 2015 at 14:00, David Ahern <dsahern@xxxxxxxxx> wrote:
> On 1/19/15 10:50 AM, Victor Kamensky wrote:
>>>
>>> diff --git a/tools/perf/util/dso.c b/tools/perf/util/dso.c
>>> index 45be944..6a2f663 100644
>>> --- a/tools/perf/util/dso.c
>>> +++ b/tools/perf/util/dso.c
>>> @@ -42,19 +42,30 @@ int dso__read_binary_type_filename(const struct dso
>>> *dso,
>>>          size_t len;
>>>
>>>          switch (type) {
>>> -       case DSO_BINARY_TYPE__DEBUGLINK: {
>>> +       case DSO_BINARY_TYPE__DEBUGLINK:
>>> +       {
>>>                  char *debuglink;
>>> -
>>> -               strncpy(filename, dso->long_name, size);
>>> -               debuglink = filename + dso->long_name_len;
>>> -               while (debuglink != filename && *debuglink != '/')
>>> -                       debuglink--;
>>> -               if (*debuglink == '/')
>>> -                       debuglink++;
>>> -               ret = filename__read_debuglink(dso->long_name, debuglink,
>>> -                                              size - (debuglink -
>>> filename));
>>> -               }
>>> +               char *filename_copy;
>>> +
>>> +               filename_copy = malloc(PATH_MAX);
>>> +               if (filename_copy) {
>>> +                       len = __symbol__join_symfs(filename, size,
>>> +                                                  dso->long_name);
>>> +                       strncpy(filename_copy, filename, PATH_MAX);
>>> +                       debuglink = filename + len;
>>> +                       while (debuglink != filename && *debuglink !=
>>> '/')
>>> +                               debuglink--;
>>> +                       if (*debuglink == '/')
>>> +                               debuglink++;
>>> +                       ret = filename__read_debuglink(filename_copy,
>>> debuglink,
>>> +                                                      size - (debuglink
>>> -
>>> +
>>> filename));
>>> +                       free(filename_copy);
>>> +               } else
>>> +                       ret = -1;
>>>                  break;
>>> +       }
>>> +
>
>
> I do not believe the filename_copy is needed; just add the symfs path to
> filename and pass filename to read_debuglink

My first version of the fix did not create filename_copy and
looked like as patch below. But then I noticed that
filename__read_debuglink function receives two pointers:

'filename' first parameter pointer to executable path from which
.gnu_debuglink sections content will be read

'debuglink' path to directory that will be updated by the function
(note  strncpy at line 531) to point to debug symbol file.

Before my change offset within 'filename' parameter of
dso__read_binary_type_filename function is passed as
'debuglink' parameter and it will be updated, and
dso->long_name is separate, passed as 'filename'
parameter to filename__read_debuglink function.

When in the first version of patch, as below, I pass filename
buffer to both (filename to open first and pointer within
filename to be updated as debuglink) as in patch
below, it will work with current implementation because
open happens first but update happens after that. But that
is specific dependency on current implementation of
filename__read_debuglink function. It did not feel quite
right to me, but practically it could be OK.

Here is the first version of the without filename_copy.
Practically I am OK with it. Please let me know if
you prefer this version: