Re: [PATCH 1/2] Look for separate debug files in debug directories under a sysroot.

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

On 2019-01-22 20:03, John Baldwin wrote:
> When an object file is present in a system root, GDB currently looks
> for separate debug files under the global debugfile directories.  For
> example, if the sysroot is set to "/myroot" and hte global debugfile
> directory is set to "/usr/lib/debug", GDB will look for a separate
> debug file for "/myroot/lib/libc.so.7" in the following paths:
> 
>   /myroot/lib/libc.so.7.debug
>   /myroot/lib/.debug/libc.so.7.debug
>   /usr/lib/debug//myroot/lib/libc.so.7.debug
>   /usr/lib/debug/lib/libc.so.7.debug
> 
> However, some system roots include a full system installation
> including a nested global debugfile directory under the sysroot.  This
> patch adds an additional check to support such systems.  In the
> example above the additional path searched is:
> 
>   /myroot/usr/lib/debug/lib/libc.so.7.debug
> 
> To try to preserve existing behavior as much as possible, this new
> path is searched last for each global debugfile directory.

I played with this a bit using a Raspbian sysroot.  I think the behavior 
you propose makes sense, perhaps more than the current behavior (I would 
be curious to see a real-word case for that one).  But anyway, keeping 
the old behavior and adding a new one is fine.  It's rather cheap to 
check many possible locations, and since there's a crc check, there's 
very little chance of loading a wrong separate debug file.

As discussed on IRC, we should probably add the same behavior for 
build-id-based separate debug files.

> diff --git a/gdb/symfile.c b/gdb/symfile.c
> index 7f800add8c..c6d2c7c537 100644
> --- a/gdb/symfile.c
> +++ b/gdb/symfile.c
> @@ -1465,6 +1465,25 @@ find_separate_debug_file (const char *dir,
>  	  if (separate_debug_file_exists (debugfile, crc32, objfile))
>  	    return debugfile;
>  	}
> +
> +      /* If the file is in the sysroot, try using its base path in the
> +	 sysroot's global debugfile directory.  */
> +      if (canon_dir != NULL
> +	  && filename_ncmp (canon_dir, gdb_sysroot,
> +			    strlen (gdb_sysroot)) == 0
> +	  && IS_DIR_SEPARATOR (canon_dir[strlen (gdb_sysroot)]))
> +	{

Is there any reason to duplicate the if above?  It looks to be the same 
as the previous check, so the new code could go in the existing if.

> +	  debugfile = target_prefix ? "target:" : "";
> +	  debugfile += gdb_sysroot;
> +	  debugfile += debugdir.get ();
> +	  debugfile += (canon_dir + strlen (gdb_sysroot));
> +	  debugfile += "/";
> +	  debugfile += debuglink;
> +
> +	  if (separate_debug_file_exists (debugfile, crc32, objfile))
> +	    return debugfile;
> +	}
> +

Simon