Re: [PATCH] elf: Get rid of alloca usage in _dl_start_profile

[Joe Simmons-Talbott <josimmon@redhat.com>]

On Fri, Sep 29, 2023 at 09:52:19AM -0400, Joe Simmons-Talbott wrote:
> Replace alloca usage with a scratch_buffer.

This was tested by enabling profiling in the build and running a test
application with LD_PROFILE defined.  I also generated a directory with
over 1024 characters and defined LD_PROFILE_OUTPUT pointing to that
directory to test the malloc path.  In both cases the .profile file was
created.  I wasn't able to process the .profile files with gprof though
as it complained about the version.

Thanks,
Joe
> ---
>  elf/dl-profile.c | 17 +++++++++++++++--
>  1 file changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/elf/dl-profile.c b/elf/dl-profile.c
> index 8be0065fbd..8ae50020bb 100644
> --- a/elf/dl-profile.c
> +++ b/elf/dl-profile.c
> @@ -22,6 +22,7 @@
>  #include <fcntl.h>
>  #include <inttypes.h>
>  #include <limits.h>
> +#include <scratch_buffer.h>
>  #include <stdio.h>
>  #include <stdlib.h>
>  #include <string.h>
> @@ -201,6 +202,8 @@ _dl_start_profile (void)
>    int s_scale;
>  #define SCALE_1_TO_1	0x10000L
>    const char *errstr = NULL;
> +  struct scratch_buffer sbuf;
> +  scratch_buffer_init (&sbuf);
>  
>    /* Compute the size of the sections which contain program code.  */
>    for (ph = GL(dl_profile_map)->l_phdr;
> @@ -318,8 +321,14 @@ _dl_start_profile (void)
>    /* First determine the output name.  We write in the directory
>       OUTPUT_DIR and the name is composed from the shared objects
>       soname (or the file name) and the ending ".profile".  */
> -  filename = (char *) alloca (strlen (GLRO(dl_profile_output)) + 1
> -			      + strlen (GLRO(dl_profile)) + sizeof ".profile");
> +  size_t filename_len = (strlen (GLRO(dl_profile_output)) + 1
> +	+ strlen (GLRO(dl_profile)) + sizeof ".profile");
> +  if (!scratch_buffer_set_array_size (&sbuf, 1, filename_len))
> +    {
> +      _dl_error_printf ("failed to allocate memory");
> +      return;
> +    }
> +  filename = sbuf.data;
>    cp = __stpcpy (filename, GLRO(dl_profile_output));
>    *cp++ = '/';
>    __stpcpy (__stpcpy (cp, GLRO(dl_profile)), ".profile");
> @@ -339,6 +348,7 @@ _dl_start_profile (void)
>  	__close_nocancel (fd);
>        _dl_error_printf (errstr, filename,
>  			__strerror_r (errnum, buf, sizeof buf));
> +      scratch_buffer_free (&sbuf);
>        return;
>      }
>  
> @@ -380,6 +390,7 @@ _dl_start_profile (void)
>  
>        _dl_error_printf ("%s: file is no correct profile data file for `%s'\n",
>  			filename, GLRO(dl_profile));
> +      scratch_buffer_free (&sbuf);
>        return;
>      }
>  
> @@ -483,6 +494,8 @@ _dl_start_profile (void)
>  
>    /* Turn on profiling.  */
>    running = 1;
> +
> +  scratch_buffer_free (&sbuf);
>  }
>  
>  
> -- 
> 2.39.2
>