Re: [commit+7.6.1] [patch] [7.6.1] Fix argv[0] symlink regression (PR 15415)

[Pedro Alves <palves at redhat dot com>]

On 09/04/2013 05:31 PM, Doug Evans wrote:
> On Wed, Sep 4, 2013 at 3:48 AM, Pedro Alves <palves@redhat.com> wrote:
>> It seems this patch introduces some output inconsistency
>> (only tried mainline):
>>
>>  $ ./gdb
>>  ...
>>  (gdb) file ./gdb
>>  Reading symbols from /home/pedro/gdb/mygit/build/gdb/gdb...done.
>>  Setting up the environment for debugging gdb.
>>  (top-gdb) info inferiors
>>    Num  Description       Executable
>>  * 1    <null>            /home/pedro/gdb/mygit/build/gdb/./gdb
>>  (top-gdb)
>>
>> Note "gdb/gdb" vs "gdb/./gdb".
>>
>>  (top-gdb) file gdbserver/../gdb
>>  Load new symbol table from "/home/pedro/gdb/mygit/build/gdb/gdb"? (y or n) y
>>  Reading symbols from /home/pedro/gdb/mygit/build/gdb/gdb...done.
>>  (top-gdb) info inferiors
>>    Num  Description       Executable
>>  * 1    <null>            /home/pedro/gdb/mygit/build/gdb/gdbserver/../gdb
>>  (top-gdb)
>>
>> Note ".../gdb/gdb" vs ".../gdb/gdbserver/../gdb".
>>
>> I tried your new series at
>> <https://sourceware.org/ml/gdb-patches/2013-08/msg00837.html>, and
>> seems there's still some inconsistency:
>>
>>  (gdb) file ./gdb
>>  Reading symbols from /home/pedro/gdb/mygit/build/gdb/./gdb...done.
>>  Setting up the environment for debugging gdb.
>>  (top-gdb) info inferiors
>>    Num  Description       Executable
>>  * 1    <null>            /home/pedro/gdb/mygit/build/gdb/./gdb
>>  (top-gdb) info files
>>  Symbols from "/home/pedro/gdb/mygit/build/gdb/./gdb".
>>  Local exec file:
>>          `/home/pedro/gdb/mygit/build/gdb/./gdb', file type elf64-x86-64.
>>
>> This one's consistent now, but then this one's odd:
>>
>>  (top-gdb) file gdbserver/../gdb
>>  Load new symbol table from "/home/pedro/gdb/mygit/build/gdb/./gdb"? (y or n) y
>>  Reading symbols from /home/pedro/gdb/mygit/build/gdb/./gdb...done.
>>
>>  (top-gdb) info inferiors
>>    Num  Description       Executable
>>  * 1    <null>            /home/pedro/gdb/mygit/build/gdb/gdbserver/../gdb
>>  (top-gdb)
>>
>> Hmm.  It seems to only happen after having loaded "./gdb" first.  This
>> sounds like related to the filename handling in the gdb/bfd cache?  GDB
>> finds reuses the same bfd (as gdbserver/../gdb is the same file as
>> the previous ./gdb), and then we printing the filename that had
>> been associated with the bfd before, instead of the one that was
>> specified in the second "file" ?
> 
> Hi.  Some random thoughts.
> 
> If the user wants to debug foo/bar/../baz, I don't mind gdb printing
> it as foo/bar/../baz.
> Other's might of course.

I don't mind either.  Opening foo/bar/../baz is not the
same as opening foo/baz, if bar is a symlink.  That's not usually
true when talking about "cd", though.

Maybe what we'll find out we need in the future is a knob users
can turn on to say "also print me the realpath in addition if it
differs from what I specified".

> 
> Removing ./ from paths is easy and reasonable enough.

Yeah, I think we should.

> 
> If gdb is debugging a new file I would have expected the old file to
> be gone from bfd's cache.

Well, or not, a valid caching policy may be to monitor memory/resource
usage, and as long as resources are available, assume the same file
will be reopened soon.  I don't really know the policy here though,
it may just be the original file is only closed after the new one
is opened.

But, the issue should trigger even if not closing the old file.
Let me check...

 (gdb) add-inferior -exec ./gdbserver/../gdb
 Added inferior 2
 Reading symbols from /home/pedro/gdb/mygit/build/gdb/./gdbserver/../gdb...done.
 Setting up the environment for debugging gdb.
 (top-gdb) add-inferior -exec ./gdb
 Added inferior 3
 Reading symbols from /home/pedro/gdb/mygit/build/gdb/./gdbserver/../gdb...done.
 (top-gdb) info inferiors
   Num  Description       Executable
   3    <null>            /home/pedro/gdb/mygit/build/gdb/./gdb
   2    <null>            /home/pedro/gdb/mygit/build/gdb/./gdbserver/../gdb
 * 1    <null>

Note it shows "gdbserver/../gdb" for inferior 3 too.

vs (new run from scratch):

 (gdb) add-inferior -exec ./gdb
 Added inferior 2
 Reading symbols from /home/pedro/gdb/mygit/build/gdb/./gdb...done.
 Setting up the environment for debugging gdb.
 (top-gdb) add-inferior -exec ./gdbserver/../gdb
 Added inferior 3
 Reading symbols from /home/pedro/gdb/mygit/build/gdb/./gdb...done.
 Setting up the environment for debugging gdb.
 (top-gdb) info inferiors
   Num  Description       Executable
   3    <null>            /home/pedro/gdb/mygit/build/gdb/./gdbserver/../gdb
   2    <null>            /home/pedro/gdb/mygit/build/gdb/./gdb
 * 1    <null>

Note it shows "./gdb" for inferior 2 too.

> [The problem may be in the sequencing.]

Yep, whatever is used first is reused.

> We do need to be consistent with which flavor of a path we use.

-- 
Pedro Alves