Re: [patch] Fix GNU/Linux core open: Can't read pathname for load map: Input/output error.

[Paul Pluzhnikov <ppluzhnikov@google.com>]

Ping?

I see this all the time, and it causes end-user confusion.


On Tue, Oct 6, 2009 at 2:45 PM, Jan Kratochvil
<jan.kratochvil@redhat.com> wrote:
> Hi,
>
> GDB currently always prints on loading a core file:
>        warning: Can't read pathname for load map: Input/output error.
>
> The patch is not nice but it was WONTFIXed on the glibc side in:
>        http://sourceware.org/ml/libc-alpha/2009-10/msg00001.html
>
> The same message in GDB PR 8882 and glibc PR 387 was for ld-linux.so.2 l_name
> but that one is now ignored thanks to IGNORE_FIRST_LINK_MAP_ENTRY.
>
> This fix is intended for Linux system vDSO l_name which is a second entry in
> the DSO list.

I believe the statement above is incorrect: the string comes from
read-only mapping of ld.so (as the comment in the patch correctly
says), and has nothing to do with vDSO.

>
> Regression tested on {x86_86,x86_64-m32,i686}-fedora11-linux-gnu.
>
>
> Thanks,
> Jan
>
>
> gdb/
> 2009-10-06  Jan Kratochvil  <jan.kratochvil@redhat.com>
>
>        Do not print false warning on reading core file with vDSO on GNU/Linux.

vDSO mention again ...

>        * solib-svr4.c (svr4_current_sos): Suppress the warning if
>        MASTER_SO_LIST is still NULL.
>        * solib.c (update_solib_list): New variable saved_so_list_head.
>        Conditionally restart the function.
>
> --- a/gdb/solib-svr4.c
> +++ b/gdb/solib-svr4.c
> @@ -1097,8 +1097,18 @@ svr4_current_sos (void)
>          target_read_string (LM_NAME (new), &buffer,
>                              SO_NAME_MAX_PATH_SIZE - 1, &errcode);
>          if (errcode != 0)
> -           warning (_("Can't read pathname for load map: %s."),
> -                    safe_strerror (errcode));
> +           {
> +             /* During the first ever DSO list reading some strings may be
> +                unreadable as residing in the ld.so readonly memory not being
> +                present in a dumped core file.  Delay the error check after
> +                the first pass of DSO list scanning when ld.so should be
> +                already mapped in and all the DSO list l_name memory gets
> +                readable.  */
> +
> +             if (master_so_list () != NULL)
> +               warning (_("Can't read pathname for load map: %s."),
> +                        safe_strerror (errcode));
> +           }
>          else
>            {
>              strncpy (new->so_name, buffer, SO_NAME_MAX_PATH_SIZE - 1);
> --- a/gdb/solib.c
> +++ b/gdb/solib.c
> @@ -538,6 +538,7 @@ update_solib_list (int from_tty, struct target_ops *target)
>   struct target_so_ops *ops = solib_ops (target_gdbarch);
>   struct so_list *inferior = ops->current_sos();
>   struct so_list *gdb, **gdb_link;
> +  struct so_list *saved_so_list_head = so_list_head;
>
>   /* We can reach here due to changing solib-search-path or the
>      sysroot, before having any inferior.  */
> @@ -668,6 +669,12 @@ update_solib_list (int from_tty, struct target_ops *target)
>          observer_notify_solib_loaded (i);
>        }
>     }
> +
> +  /* If this was the very first DSO list scan and we possibly read in ld.so
> +     recheck all the formerly unreadable DSO names strings.  */
> +
> +  if (saved_so_list_head == NULL && so_list_head != NULL)
> +    update_solib_list (from_tty, target);
>  }
>
>
>



-- 
Paul Pluzhnikov