Re: [PATCH] gdb, btrace: improve error messages

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

On 2022-02-01 07:10, Markus Metzger via Gdb-patches wrote:
> When trying to use 'record btrace' on a system that does not support it,
> the error message isn't as clear as it could be.  See
> https://sourceware.org/pipermail/gdb/2022-January/049870.html.
> 
> Improve the error message in a few cases.
> 
> Reported-by: Simon Sobisch  <simonsobisch@gnu.org>
> ---
>  gdb/nat/linux-btrace.c | 17 +++++++++++++++--
>  1 file changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/gdb/nat/linux-btrace.c b/gdb/nat/linux-btrace.c
> index d8880756aad..13ed493495d 100644
> --- a/gdb/nat/linux-btrace.c
> +++ b/gdb/nat/linux-btrace.c
> @@ -429,7 +429,7 @@ diagnose_perf_event_open_fail ()
>  	static const char filename[] = "/proc/sys/kernel/perf_event_paranoid";
>  	gdb_file_up file = gdb_fopen_cloexec (filename, "r");
>  	if (file.get () == nullptr)
> -	  break;
> +	  error (_("Your system does not support process recording."));
>  
>  	int level, found = fscanf (file.get (), "%d", &level);
>  	if (found == 1 && level > 2)
> @@ -571,7 +571,20 @@ perf_event_pt_event_type ()
>    errno = 0;
>    gdb_file_up file = gdb_fopen_cloexec (filename, "r");
>    if (file.get () == nullptr)
> -    error (_("Failed to open %s: %s."), filename, safe_strerror (errno));
> +    switch (errno)
> +      {
> +      case EACCES:
> +      case EFAULT:
> +      case EPERM:
> +	error (_("You do not have permission to use Intel PT."));
> +
> +      case ENOTDIR:
> +      case ENOENT:
> +	error (_("Your system does not support Intel PT."));
> +
> +      default:
> +	error (_("Failed to open %s: %s."), filename, safe_strerror (errno));
> +      }
>  
>    int type, found = fscanf (file.get (), "%d", &type);
>    if (found != 1)

I think the more detailed messages are nice.  But I would still mention
the underlying error, to indicate how GDB reached that conclusion.  That
gives the user has something to grab onto to understand and fix the
problem.  For example:

  Failed to open %s (%s).  You do not have permission to use Intel PT.

where the %s are respectively the filename and the strerror.

Simon