mtrace: Use a static buffer for printing [BZ #25947]

Message ID 20210722132430.1945153-1-siddhesh@sourceware.org
State New
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Series
  • mtrace: Use a static buffer for printing [BZ #25947]
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Commit Message

Florian Weimer via Libc-alpha July 22, 2021, 1:24 p.m.
Use a static buffer for mtrace printing now that it no longer adds to
default libc footprint.
---
 malloc/mtrace-impl.c | 14 +++-----------
 1 file changed, 3 insertions(+), 11 deletions(-)

-- 
2.31.1

Comments

Florian Weimer via Libc-alpha Aug. 11, 2021, 7:41 a.m. | #1
Ping!

On 7/22/21 6:54 PM, Siddhesh Poyarekar via Libc-alpha wrote:
> Use a static buffer for mtrace printing now that it no longer adds to

> default libc footprint.

> ---

>   malloc/mtrace-impl.c | 14 +++-----------

>   1 file changed, 3 insertions(+), 11 deletions(-)

> 

> diff --git a/malloc/mtrace-impl.c b/malloc/mtrace-impl.c

> index 0e10ab7f60..83008ca18f 100644

> --- a/malloc/mtrace-impl.c

> +++ b/malloc/mtrace-impl.c

> @@ -34,11 +34,8 @@

>   

>   #include <kernel-features.h>

>   

> -#define TRACE_BUFFER_SIZE 512

> -

>   static FILE *mallstream;

>   static const char mallenv[] = "MALLOC_TRACE";

> -static char *malloc_trace_buffer;

>   

>   static void

>   tr_where (const void *caller, Dl_info *info)

> @@ -184,16 +181,13 @@ do_mtrace (void)

>     mallfile = secure_getenv (mallenv);

>     if (mallfile != NULL)

>       {

> -      char *mtb = malloc (TRACE_BUFFER_SIZE);

> -      if (mtb == NULL)

> -        return;

> -

>         mallstream = fopen (mallfile != NULL ? mallfile : "/dev/null", "wce");

>         if (mallstream != NULL)

>           {

>             /* Be sure it doesn't malloc its buffer!  */

> -          malloc_trace_buffer = mtb;

> -          setvbuf (mallstream, malloc_trace_buffer, _IOFBF, TRACE_BUFFER_SIZE);

> +	  static char tracebuf [512];

> +

> +	  setvbuf (mallstream, tracebuf, _IOFBF, sizeof (tracebuf));

>             fprintf (mallstream, "= Start\n");

>             if (!added_atexit_handler)

>               {

> @@ -203,8 +197,6 @@ do_mtrace (void)

>               }

>   	  __malloc_debug_enable (MALLOC_MTRACE_HOOK);

>           }

> -      else

> -        free (mtb);

>       }

>   }

>   

>
Florian Weimer via Libc-alpha Aug. 11, 2021, 4:55 p.m. | #2
Siddhesh Poyarekar via Libc-alpha <libc-alpha@sourceware.org> writes:
> -#define TRACE_BUFFER_SIZE 512


I think it would be prudent to keep this, instead of hard-coding the 512
in the code below.  I don't feel strongly about it, since the 512 only
appears once.

> -static char *malloc_trace_buffer;


We could have kept this here, too, but I have no real preference about
it.

> -      char *mtb = malloc (TRACE_BUFFER_SIZE);

> -      if (mtb == NULL)

> -        return;


Ok.

>            /* Be sure it doesn't malloc its buffer!  */

> -          malloc_trace_buffer = mtb;

> -          setvbuf (mallstream, malloc_trace_buffer, _IOFBF, TRACE_BUFFER_SIZE);

> +	  static char tracebuf [512];

> +

> +	  setvbuf (mallstream, tracebuf, _IOFBF, sizeof (tracebuf));


_IOFBF is same as before, so OK, but I wonder if _IOLBF (line buffered)
would be more user-friendly?  I can't think of a use case for piping the
output through "tail -f" or something, and actually needing to wait for
it, but it's text output.

> -      else

> -        free (mtb);


Ok.

LGTM as-is, my comments are for pondering only ;-)

Reviewed-by: DJ Delorie <dj@redhat.com>

Patch

diff --git a/malloc/mtrace-impl.c b/malloc/mtrace-impl.c
index 0e10ab7f60..83008ca18f 100644
--- a/malloc/mtrace-impl.c
+++ b/malloc/mtrace-impl.c
@@ -34,11 +34,8 @@ 
 
 #include <kernel-features.h>
 
-#define TRACE_BUFFER_SIZE 512
-
 static FILE *mallstream;
 static const char mallenv[] = "MALLOC_TRACE";
-static char *malloc_trace_buffer;
 
 static void
 tr_where (const void *caller, Dl_info *info)
@@ -184,16 +181,13 @@  do_mtrace (void)
   mallfile = secure_getenv (mallenv);
   if (mallfile != NULL)
     {
-      char *mtb = malloc (TRACE_BUFFER_SIZE);
-      if (mtb == NULL)
-        return;
-
       mallstream = fopen (mallfile != NULL ? mallfile : "/dev/null", "wce");
       if (mallstream != NULL)
         {
           /* Be sure it doesn't malloc its buffer!  */
-          malloc_trace_buffer = mtb;
-          setvbuf (mallstream, malloc_trace_buffer, _IOFBF, TRACE_BUFFER_SIZE);
+	  static char tracebuf [512];
+
+	  setvbuf (mallstream, tracebuf, _IOFBF, sizeof (tracebuf));
           fprintf (mallstream, "= Start\n");
           if (!added_atexit_handler)
             {
@@ -203,8 +197,6 @@  do_mtrace (void)
             }
 	  __malloc_debug_enable (MALLOC_MTRACE_HOOK);
         }
-      else
-        free (mtb);
     }
 }