Re: [PATCH v3] [PR gdb/27614] gdb-add-index fails on symlinks.

[Simon Marchi <simon.marchi@polymtl.ca>]

On 2021-03-27 1:27 p.m., Lancelot SIX via Gdb-patches wrote:
> Since V2:
>         - Use GDB to follow symlink instead of readlink. Unlike
>           readlink, GDB is guaranteed to be available.
> 
> Since V1:
>         - Replace '&>/dev/null' with '>/dev/null 2>&1'
> 
> --
> 
> PR 27614 shows that gdb-add-index fails to generate the index when its
> argument is a symlink.
> 
> The following one liner illustrates the reported problem:
> 
>         $ echo 'int main(){}'|gcc -g -x c -;ln -s a.out symlink;gdb-add-index symlink
>         gdb-add-index: No index was created for symlink
>         gdb-add-index: [Was there no debuginfo? Was there already an index?]
>         $ ls -l
>         -rwxr-xr-x 1 25712 Mar 19 23:05 a.out*
>         -rw------- 1  8277 Mar 19 23:05 a.out.gdb-index
>         lrwxrwxrwx 1     5 Mar 19 23:05 symlink -> a.out*
> 
> GDB generates the .gdb-index file with a name that matches the name of
> the actual program (a.out.gdb-index here), not the symlink that
> references it.  The remaining of the script is looking for a file named
> after the provided argument (would be 'symlink.gdb-index' in our
> example).
> 
> The common option to solve such issue would be to use readlink to follow
> the symlink.  Unfortunately, this command is not available in the POSIX
> standard.  This commit therefore proposes to use GDB itself to identify
> where the symlink points to.  This requires some parsing of GDB output.
> The added test should be enough to detect regression if GDB where to
> change the way it formats its output.

I preferred your previous approach, compared to relying on a maintenance
command.  Relying on a maintenance command is fine in tests, for example,
but here somebody could use gdb-add-index from a given GDB version with
a GDB of a different version.

  GDB=/my/newer/gdb gdb-add-index a.out

In the previous review, you said:

>> Would it work with just `readlink <file>`?

> This would fail if $file is a symlink to a symlink.  This is what
> ldconfig usually does (libfoo.so -> libfoo.so.x -> libfoo.so.x.y).

Can't you just call it in a loop then?

  while file is a symlink:
    file=readlink $file

Simon