Re: [PATCH] Properly detect working jobserver in gcc driver.

[Jakub Jelinek <jakub at redhat dot com>]

On Fri, Aug 02, 2019 at 10:47:10AM +0200, Martin Liška wrote:
> > Can you strace if other fds are opened and not closed in the spot you had it
> > before?  Advantage of doing it there is that it will not be done for all the
> > -E/-S/-c compilations when the linker is not spawned.
> 
> I've used the same trick which you used and I'm attaching the output.
> I believe it's fine, I can't see any opened fd by GCC.

LGTM.

> gcc/ChangeLog:
> 
> 2019-08-02  Martin Liska  <mliska@suse.cz>
> 
> 	* gcc.c (driver::maybe_run_linker): Call detect_jobserver
> 	to detect working job server.
> 	(driver::detect_jobserver): Test whether jobserver
> 	is active from GCC driver. That will prevent situation where
> 	GCC is invoked from a LD plugin and the linker already uses
> 	file descriptors suggested by make.  That leads to a wrong
> 	detection.
> 	* gcc.h (driver): Add detect_jobserver.
> 	* lto-wrapper.c (jobserver_active_p): Simplify sscanf by
> 	not scanning for --jobserver-auth prefix.
> ---
>  gcc/gcc.c         | 42 ++++++++++++++++++++++++++++++++++++++++++
>  gcc/gcc.h         |  1 +
>  gcc/lto-wrapper.c |  2 +-
>  3 files changed, 44 insertions(+), 1 deletion(-)
> 
> diff --git a/gcc/gcc.c b/gcc/gcc.c
> index a4323eb146e..18a07426290 100644
> --- a/gcc/gcc.c
> +++ b/gcc/gcc.c
> @@ -8268,6 +8268,8 @@ driver::maybe_run_linker (const char *argv0) const
>      {
>        int tmp = execution_count;
>  
> +      detect_jobserver ();
> +
>        if (! have_c)
>  	{
>  #if HAVE_LTO_PLUGIN > 0
> @@ -8357,6 +8359,46 @@ driver::final_actions () const
>      }
>  }
>  
> +/* Detect whether jobserver is active and working.  If not drop
> +   --jobserver-auth from MAKEFLAGS.  */
> +
> +void
> +driver::detect_jobserver () const
> +{
> +  /* Detect jobserver and drop it if it's not working.  */
> +  const char *makeflags = env.get ("MAKEFLAGS");
> +  if (makeflags != NULL)
> +    {
> +      const char *needle = "--jobserver-auth=";
> +      const char *n = strstr (makeflags, needle);
> +      if (n != NULL)
> +	{
> +	  int rfd = -1;
> +	  int wfd = -1;
> +
> +	  bool jobserver
> +	    = (sscanf (n + strlen (needle), "%d,%d", &rfd, &wfd) == 2
> +	       && rfd > 0
> +	       && wfd > 0
> +	       && fcntl (rfd, F_GETFD) >= 0
> +	       && fcntl (wfd, F_GETFD) >= 0);
> +
> +	  /* Drop the jobserver if it's not working now.  */
> +	  if (!jobserver)
> +	    {
> +	      unsigned offset = n - makeflags;
> +	      char *dup = xstrdup (makeflags);
> +	      dup[offset] = '\0';
> +
> +	      const char *space = strchr (makeflags + offset, ' ');
> +	      if (space != NULL)
> +		strcpy (dup + offset, space);
> +	      xputenv (concat ("MAKEFLAGS=", dup, NULL));
> +	    }
> +	}
> +    }
> +}
> +
>  /* Determine what the exit code of the driver should be.  */
>  
>  int
> diff --git a/gcc/gcc.h b/gcc/gcc.h
> index a0a1d94c6e6..dc77dba67fb 100644
> --- a/gcc/gcc.h
> +++ b/gcc/gcc.h
> @@ -51,6 +51,7 @@ class driver
>    void do_spec_on_infiles () const;
>    void maybe_run_linker (const char *argv0) const;
>    void final_actions () const;
> +  void detect_jobserver () const;
>    int get_exit_code () const;
>  
>   private:
> diff --git a/gcc/lto-wrapper.c b/gcc/lto-wrapper.c
> index 353187c6043..3414adedd26 100644
> --- a/gcc/lto-wrapper.c
> +++ b/gcc/lto-wrapper.c
> @@ -1234,7 +1234,7 @@ jobserver_active_p (void)
>    int rfd = -1;
>    int wfd = -1;
>  
> -  return ((sscanf(n, "--jobserver-auth=%d,%d", &rfd, &wfd) == 2)
> +  return (sscanf (n + strlen (needle), "%d,%d", &rfd, &wfd) == 2
>  	  && rfd > 0
>  	  && wfd > 0
>  	  && fcntl (rfd, F_GETFD) >= 0
> -- 
> 2.22.0
> 


	Jakub