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

Simon Marchi
2019-01-26T05:17:03Z

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