Re: [PATCH v2 (w/ ChangeLog)] Fix disabling of solib probes when LD_AUDITing

[Simon Marchi <simark@simark.ca>]

On 2019-12-14 7:12 p.m., George Barrett wrote:
> The SVR4 solib event handler determines whether an event is related to a
> non-base link namespace by comparing the event's debug struct address
> to the debug struct address of the initial program image. However, this
> can fail when using LD_AUDIT as audit libraries are loaded before the
> loader has initialised the initial program image's debug struct. When
> the event handler fails to find the debug struct, the probe-based
> debugger interface is disabled and a warning is flagged to the user.
> 
> This commit adds a fallback test to help determine whether an event is
> for a foreign link namespace when the debug struct isn't available.

Hi George,

The patch makes sense to me, as far as I understand it.

> gdb/ChangeLog:
> 2019-12-15  George Barrett  <bob@bob131.so>
> 
> 	* solib-svr4.c (svr4_handle_solib_event): Add fallback link
> 	namespace test for when the debug struct isn't available.
> ---
>  gdb/solib-svr4.c | 22 +++++++++++++++++++++-
>  1 file changed, 21 insertions(+), 1 deletion(-)
> 
> diff --git a/gdb/solib-svr4.c b/gdb/solib-svr4.c
> index de765576d0..f0c7769ac2 100644
> --- a/gdb/solib-svr4.c
> +++ b/gdb/solib-svr4.c
> @@ -1942,7 +1942,27 @@ svr4_handle_solib_event (void)
>      /* Always locate the debug struct, in case it moved.  */
>      info->debug_base = 0;
>      if (locate_base (info) == 0)
> -      return;
> +      {
> +	/* It's possible for the reloc_complete probe to be triggered before
> +	   the linker has set the DT_DEBUG pointer (for example, when the
> +	   linker has finished relocating an LD_AUDIT library or its
> +	   dependencies).  Since we can't yet handle libraries from other link
> +	   namespaces, we don't lose anything by ignoring them here.  */
> +	struct value *link_map_id_val;
> +	try
> +	  {
> +	    link_map_id_val = pa->prob->evaluate_argument (0, frame);
> +	  }
> +	catch (const gdb_exception_error)

Catch the exception by reference:

  catch (const gdb_exception_error &)

I can push your patch with this fixed, if you agree (and others think the patch is
fine too).

Simon