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SubjectRe: [PATCH] perf symbols: Follow .gnu_debuglink section to find separate symbols
Em Wed, Jun 20, 2012 at 03:22:41PM -0700, Pierre-Loup A. Griffais escreveu:
> The .gnu_debuglink section is specified to contain the filename of the
> debug info file, as well as a CRC that can be used to validate it.

> This provides more context:
> +++ b/tools/perf/util/symbol.c
> +static int filename__read_debuglink(const char *filename,
> + char *path, size_t size)
> +{

Isn't there any other function that opens an ELF file, looks for an
specific session to then read its contents?

Couldn't it be reused here?

> + char *last_slash;
> + strncpy(name, dso->long_name, size);
> + last_slash = name + dso->long_name_len;
> + while (last_slash && *last_slash != '/')
> + last_slash--;

Why the test for last_slash to be != NULL? How could it ever be? This is
an optimization since we have the dso->long_name_len so that we avoid
using strrchr that in turn would do an strlen?

So the test should be:

while (last_slash != name && *last_slash != '/')

To avoid underflowing, right?

> + if (last_slash)
> + last_slash++;
> + filename__read_debuglink(dso->long_name, last_slash,

How last_slash can point to the path? It looks like it points to the
basename, no?

Yeah, it is, and then your algorithm will work because last_slash
doesn't point to the _path_, but to a string _preceded_ by the path, so
for /bin/ls, the debuglink content would be ls.debug and that is what
will be stashed there, ending up with:

name = "/bin/\0"
name = "/bin/ls.debug\0"

I.e. its not really the last slash, but where the debuglink content has
to be stashed, concatenating with the same dirname as the associated

Can you please rename "last_slash" to "debuglink"? And "path" to
"debuglink" as well in the routine that reads the debuglink.

> + size - (last_slash - name));
> + }

Other than that, thanks a lot for working on this, surely we have to
support this feature!

- ARnaldo

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