[PATCH] Fix LD_DEBUG=statistics on x86-64

[PATCH] Fix LD_DEBUG=statistics on x86-64

[Jakub Jelinek]

Hi!

     17214:     runtime linker statistics:
     17214:       total startup time in dynamic loader: 12434 clock cycles
     17214:                 time needed for relocation: 280243 clock cycles (%)
     17214:                      number of relocations: 98
     17214:           number of relocations from cache: 3
     17214:             number of relative relocations: 1286
     17214:                time needed to load objects: 0 clock cycles (.0%)
certainly doesn't look correct.
The problem is that without volatile in the rdtsc asm GCC happily merges
HP_TIMING_NOW (start);
call something
HP_TIMING_NOW (stop);
so that stop == start (rdtsc done only before the call).

     17232:     runtime linker statistics:
     17232:       total startup time in dynamic loader: 733738 clock cycles
     17232:                 time needed for relocation: 278644 clock cycles (37.9%)
     17232:                      number of relocations: 83
     17232:           number of relocations from cache: 3
     17232:             number of relative relocations: 1295
     17232:                time needed to load objects: 326662 clock cycles (44.5%)

looks better.

2004-03-17  Jakub Jelinek  <jakub@redhat.com>

	* sysdeps/x86_64/hp-timing.h (HP_TIMING_NOW): Make asm volatile.

--- libc/sysdeps/x86_64/hp-timing.h.jj	2002-08-31 01:09:29.000000000 +0200
+++ libc/sysdeps/x86_64/hp-timing.h	2004-03-17 13:26:02.139127766 +0100
@@ -1,5 +1,5 @@
 /* High precision, low overhead timing functions.  x86-64 version.
-   Copyright (C) 2002 Free Software Foundation, Inc.
+   Copyright (C) 2002, 2004 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
 
    The GNU C Library is free software; you can redistribute it and/or
@@ -25,7 +25,8 @@
 /* The "=A" constraint used in 32-bit mode does not work in 64-bit mode.  */
 # undef HP_TIMING_NOW
 # define HP_TIMING_NOW(Var) \
-  ({ unsigned int _hi, _lo; asm ("rdtsc" : "=a" (_lo), "=d" (_hi)); \
+  ({ unsigned int _hi, _lo; \
+     asm volatile ("rdtsc" : "=a" (_lo), "=d" (_hi)); \
      (Var) = ((unsigned long long int) _hi << 32) | _lo; })
 
 /* The funny business for 32-bit mode is not required here.  */

	Jakub

Re: [PATCH] Fix LD_DEBUG=statistics on x86-64

[Ulrich Drepper]

Jakub Jelinek wrote:

> 	* sysdeps/x86_64/hp-timing.h (HP_TIMING_NOW): Make asm volatile.

Applied.

-- 
➧ Ulrich Drepper ➧ Red Hat, Inc. ➧ 444 Castro St ➧ Mountain View, CA ❖