[igt-dev] [PATCH i-g-t] lib/igt_core: Detect gdb harder

[Chris Wilson]

Quoting Ville Syrjala (2020-01-22 16:43:32)
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> The current gdb detection only works for the parent igt process,
> but none of its children will see the gdb and so won't trap properly
> in igt_fail_assert(). Also we will not detect gdb if it was attached
> after the fact. Fix all of that by looking for the "TracerPid"
> information in /proc/<pid>/status. We'll leave the current "assume
> parent may be gdb" approach as a fallback.
> 
> Also annoyingly by default gdb will only track a single process.
> To make it track all of them, and let them all run simultanously
> one needs the following incantations:
>  set detach-on-fork off
>  set schedule-multiple on
> 
> Maybe that will save someone from having to trawl as many
> docs/gogole hits as I did.
> 
> Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> ---
>  lib/igt_core.c | 38 ++++++++++++++++++++++++++++++++++++--
>  1 file changed, 36 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/igt_core.c b/lib/igt_core.c
> index 0a0068946a6a..109b5926eac4 100644
> --- a/lib/igt_core.c
> +++ b/lib/igt_core.c
> @@ -1609,12 +1609,12 @@ void igt_describe_f(const char *fmt, ...)
>         assert(ret < sizeof(__current_description));
>  }
>  
> -static bool running_under_gdb(void)
> +static bool is_gdb(pid_t pid)
>  {
>         char pathname[30], buf[1024];
>         ssize_t len;
>  
> -       sprintf(pathname, "/proc/%d/exe", getppid());
> +       sprintf(pathname, "/proc/%d/exe", pid);
>         len = readlink(pathname, buf, sizeof(buf) - 1);
>         if (len < 0)
>                 return false;
> @@ -1624,6 +1624,40 @@ static bool running_under_gdb(void)
>         return strncmp(basename(buf), "gdb", 3) == 0;
>  }
>  
> +static pid_t tracer_pid(void)
> +{
> +       char pathname[30];
> +       pid_t pid = 0;
> +       FILE *f;
> +
> +       sprintf(pathname, "/proc/%d/status", getpid());
> +
> +       f = fopen(pathname, "r");
> +       if (!f)
> +               return getppid();
> +
> +       for (;;) {
> +               char buf[1024];
> +               char *s;
> +
> +               s = fgets(buf, sizeof(buf), f);

I'd prefer fgetline, /proc/<pid>status is >1024 bytes so there's always
that chance we cut the TracerPid line.

> +               if (!s)
> +                       break;
> +
> +               if (sscanf(s, "TracerPid: %d", &pid) == 1)
> +                       break;
> +       }
> +
> +       fclose(f);
> +
> +       return pid ?: getppid();

Makes sense.

> +}
> +
> +static bool running_under_gdb(void)
> +{

/*
 * Annoyingly by default gdb will only track a single process.
 * To make it track all of them, and let them all run simultaneously
 * one needs the following incantations:
 *   set detach-on-fork off
 *   set schedule-multiple on
 */


TIL two things, so
Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
-Chris