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[PING][PATCH] Fix strcpy_chk and stpcpy_chk performance.


ping
On Wed, Aug 12, 2015 at 08:42:13AM +0200, OndÅej BÃlka wrote:
> Hi, as I wrote in previous patches a performance of checked strcpy and
> stpcpy is terrible as these don't use sse2 and are around four times
> slower that strcpy and stpcpy now.
> 
> As this bug shows that these functions are not performance sensitive I
> decided just to improve generic implementation instead for easier
> maintainance.
> 
> I could improve performance more if we allow to write past bound and
> then fail as we could just call stpcpy and check if it exceed bounds or
> not.
> 
> Other arches could also have bad performance so sobebody should finally
> read benchtests there to see problems.
> 
> 	* debug/strcpy_chk.c: Improve performance.
> 	* debug/stpcpy_chk.c: Likewise.
> 	* sysdeps/x86_64/strcpy_chk.S: Remove.
> 	* sysdeps/x86_64/stpcpy_chk.S: Remove.
> 
> diff --git a/debug/stpcpy_chk.c b/debug/stpcpy_chk.c
> index 91c5031..69476a2 100644
> --- a/debug/stpcpy_chk.c
> +++ b/debug/stpcpy_chk.c
> @@ -29,16 +29,9 @@ __stpcpy_chk (dest, src, destlen)
>       const char *src;
>       size_t destlen;
>  {
> -  char *d = dest;
> -  const char *s = src;
> -
> -  do
> -    {
> -      if (__glibc_unlikely (destlen-- == 0))
> -	__chk_fail ();
> -      *d++ = *s;
> -    }
> -  while (*s++ != '\0');
> -
> -  return d - 1;
> +  size_t len = strlen (src);
> +  if (len > destlen)
> +    __chk_fail ();
> +    
> +  return memcpy (dest, src, len + 1) + len;
>  }
> diff --git a/debug/strcpy_chk.c b/debug/strcpy_chk.c
> index 91bf0dd..92eb69d2 100644
> --- a/debug/strcpy_chk.c
> +++ b/debug/strcpy_chk.c
> @@ -28,40 +28,9 @@ __strcpy_chk (dest, src, destlen)
>       const char *src;
>       size_t destlen;
>  {
> -  char c;
> -  char *s = (char *) src;
> -  const ptrdiff_t off = dest - s;
> -
> -  while (__builtin_expect (destlen >= 4, 0))
> -    {
> -      c = s[0];
> -      s[off] = c;
> -      if (c == '\0')
> -        return dest;
> -      c = s[1];
> -      s[off + 1] = c;
> -      if (c == '\0')
> -        return dest;
> -      c = s[2];
> -      s[off + 2] = c;
> -      if (c == '\0')
> -        return dest;
> -      c = s[3];
> -      s[off + 3] = c;
> -      if (c == '\0')
> -        return dest;
> -      destlen -= 4;
> -      s += 4;
> -    }
> -
> -  do
> -    {
> -      if (__glibc_unlikely (destlen-- == 0))
> -        __chk_fail ();
> -      c = *s;
> -      *(s++ + off) = c;
> -    }
> -  while (c != '\0');
> -
> -  return dest;
> +  size_t len = strlen (src);
> +  if (len > destlen)
> +    __chk_fail ();
> +    
> +  return memcpy (dest, src, len + 1);
>  }
> diff --git a/sysdeps/x86_64/stpcpy_chk.S b/sysdeps/x86_64/stpcpy_chk.S
> deleted file mode 100644
> index 905e8d7..0000000
> --- a/sysdeps/x86_64/stpcpy_chk.S
> +++ /dev/null
> @@ -1,3 +0,0 @@
> -#define USE_AS_STPCPY_CHK
> -#define STRCPY_CHK __stpcpy_chk
> -#include <sysdeps/x86_64/strcpy_chk.S>
> diff --git a/sysdeps/x86_64/strcpy_chk.S b/sysdeps/x86_64/strcpy_chk.S
> deleted file mode 100644
> index 24e51c6..0000000
> --- a/sysdeps/x86_64/strcpy_chk.S
> +++ /dev/null
> @@ -1,208 +0,0 @@
> -/* strcpy/stpcpy checking implementation for x86-64.
> -   Copyright (C) 2002-2015 Free Software Foundation, Inc.
> -   This file is part of the GNU C Library.
> -   Contributed by Andreas Jaeger <aj@suse.de>, 2002.
> -   Adopted into checking version by Jakub Jelinek <jakub@redhat.com>.
> -
> -   The GNU C Library is free software; you can redistribute it and/or
> -   modify it under the terms of the GNU Lesser General Public
> -   License as published by the Free Software Foundation; either
> -   version 2.1 of the License, or (at your option) any later version.
> -
> -   The GNU C Library is distributed in the hope that it will be useful,
> -   but WITHOUT ANY WARRANTY; without even the implied warranty of
> -   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> -   Lesser General Public License for more details.
> -
> -   You should have received a copy of the GNU Lesser General Public
> -   License along with the GNU C Library; if not, see
> -   <http://www.gnu.org/licenses/>.  */
> -
> -#include <sysdep.h>
> -#include "asm-syntax.h"
> -
> -#ifndef USE_AS_STPCPY_CHK
> -# define STRCPY_CHK __strcpy_chk
> -#endif
> -
> -	.text
> -ENTRY (STRCPY_CHK)
> -	movq	%rsi, %rcx	/* Source register. */
> -	andl	$7, %ecx	/* mask alignment bits */
> -#ifndef USE_AS_STPCPY_CHK
> -	movq	%rdi, %r10	/* Duplicate destination pointer.  */
> -#endif
> -	jz 5f			/* aligned => start loop */
> -
> -	cmpq	$8, %rdx	/* Check if only few bytes left in
> -				   destination.  */
> -	jb	50f
> -
> -	subq	$8, %rcx	/* We need to align to 8 bytes.  */
> -	addq	%rcx, %rdx	/* Subtract count of stored bytes
> -				   in the cycle below from destlen.  */
> -
> -	/* Search the first bytes directly.  */
> -0:
> -	movb	(%rsi), %al	/* Fetch a byte */
> -	testb	%al, %al	/* Is it NUL? */
> -	movb	%al, (%rdi)	/* Store it */
> -	jz	4f		/* If it was NUL, done! */
> -	incq	%rsi
> -	incq	%rdi
> -	incl	%ecx
> -	jnz	0b
> -
> -5:
> -	movq $0xfefefefefefefeff,%r8
> -	cmpq	$32, %rdx	/* Are there enough bytes in destination
> -				   for the next unrolled round?  */
> -	jb	60f		/* If not, avoid the unrolled loop.  */
> -
> -	/* Now the sources is aligned.  Unfortunatly we cannot force
> -	   to have both source and destination aligned, so ignore the
> -	   alignment of the destination.  */
> -	.p2align 4
> -1:
> -	/* 1st unroll.  */
> -	movq	(%rsi), %rax	/* Read double word (8 bytes).  */
> -	addq	$8, %rsi	/* Adjust pointer for next word.  */
> -	movq	%rax, %r9	/* Save a copy for NUL finding.  */
> -	addq	%r8, %r9	/* add the magic value to the word.  We get
> -				   carry bits reported for each byte which
> -				   is *not* 0 */
> -	jnc	3f		/* highest byte is NUL => return pointer */
> -	xorq	%rax, %r9	/* (word+magic)^word */
> -	orq	%r8, %r9	/* set all non-carry bits */
> -	incq	%r9		/* add 1: if one carry bit was *not* set
> -				   the addition will not result in 0.  */
> -
> -	jnz	3f		/* found NUL => return pointer */
> -
> -	movq	%rax, (%rdi)	/* Write value to destination.  */
> -	addq	$8, %rdi	/* Adjust pointer.  */
> -
> -	/* 2nd unroll.  */
> -	movq	(%rsi), %rax	/* Read double word (8 bytes).  */
> -	addq	$8, %rsi	/* Adjust pointer for next word.  */
> -	movq	%rax, %r9	/* Save a copy for NUL finding.  */
> -	addq	%r8, %r9	/* add the magic value to the word.  We get
> -				   carry bits reported for each byte which
> -				   is *not* 0 */
> -	jnc	3f		/* highest byte is NUL => return pointer */
> -	xorq	%rax, %r9	/* (word+magic)^word */
> -	orq	%r8, %r9	/* set all non-carry bits */
> -	incq	%r9		/* add 1: if one carry bit was *not* set
> -				   the addition will not result in 0.  */
> -
> -	jnz	3f		/* found NUL => return pointer */
> -
> -	movq	%rax, (%rdi)	/* Write value to destination.  */
> -	addq	$8, %rdi	/* Adjust pointer.  */
> -
> -	/* 3rd unroll.  */
> -	movq	(%rsi), %rax	/* Read double word (8 bytes).  */
> -	addq	$8, %rsi	/* Adjust pointer for next word.  */
> -	movq	%rax, %r9	/* Save a copy for NUL finding.  */
> -	addq	%r8, %r9	/* add the magic value to the word.  We get
> -				   carry bits reported for each byte which
> -				   is *not* 0 */
> -	jnc	3f		/* highest byte is NUL => return pointer */
> -	xorq	%rax, %r9	/* (word+magic)^word */
> -	orq	%r8, %r9	/* set all non-carry bits */
> -	incq	%r9		/* add 1: if one carry bit was *not* set
> -				   the addition will not result in 0.  */
> -
> -	jnz	3f		/* found NUL => return pointer */
> -
> -	movq	%rax, (%rdi)	/* Write value to destination.  */
> -	addq	$8, %rdi	/* Adjust pointer.  */
> -
> -	/* 4th unroll.  */
> -	movq	(%rsi), %rax	/* Read double word (8 bytes).  */
> -	addq	$8, %rsi	/* Adjust pointer for next word.  */
> -	movq	%rax, %r9	/* Save a copy for NUL finding.  */
> -	addq	%r8, %r9	/* add the magic value to the word.  We get
> -				   carry bits reported for each byte which
> -				   is *not* 0 */
> -	jnc	3f		/* highest byte is NUL => return pointer */
> -	xorq	%rax, %r9	/* (word+magic)^word */
> -	orq	%r8, %r9	/* set all non-carry bits */
> -	incq	%r9		/* add 1: if one carry bit was *not* set
> -				   the addition will not result in 0.  */
> -
> -	jnz	3f		/* found NUL => return pointer */
> -
> -	subq	$32, %rdx	/* Adjust destlen.  */
> -	movq	%rax, (%rdi)	/* Write value to destination.  */
> -	addq	$8, %rdi	/* Adjust pointer.  */
> -	cmpq	$32, %rdx	/* Are there enough bytes in destination
> -				   for the next unrolled round?  */
> -	jae	1b		/* Next iteration.  */
> -
> -60:
> -	cmpq	$8, %rdx	/* Are there enough bytes in destination
> -				   for the next unrolled round?  */
> -	jb	50f		/* Now, copy and check byte by byte.  */
> -
> -	movq	(%rsi), %rax	/* Read double word (8 bytes).  */
> -	addq	$8, %rsi	/* Adjust pointer for next word.  */
> -	movq	%rax, %r9	/* Save a copy for NUL finding.  */
> -	addq	%r8, %r9	/* add the magic value to the word.  We get
> -				   carry bits reported for each byte which
> -				   is *not* 0 */
> -	jnc	3f		/* highest byte is NUL => return pointer */
> -	xorq	%rax, %r9	/* (word+magic)^word */
> -	orq	%r8, %r9	/* set all non-carry bits */
> -	incq	%r9		/* add 1: if one carry bit was *not* set
> -				   the addition will not result in 0.  */
> -
> -	jnz	3f		/* found NUL => return pointer */
> -
> -	subq	$8, %rdx	/* Adjust destlen.  */
> -	movq	%rax, (%rdi)	/* Write value to destination.  */
> -	addq	$8, %rdi	/* Adjust pointer.  */
> -	jmp	60b		/* Next iteration.  */
> -
> -	/* Do the last few bytes. %rax contains the value to write.
> -	   The loop is unrolled twice.  */
> -	.p2align 4
> -3:
> -	/* Note that stpcpy needs to return with the value of the NUL
> -	   byte.  */
> -	movb	%al, (%rdi)	/* 1st byte.  */
> -	testb	%al, %al	/* Is it NUL.  */
> -	jz	4f		/* yes, finish.  */
> -	incq	%rdi		/* Increment destination.  */
> -	movb	%ah, (%rdi)	/* 2nd byte.  */
> -	testb	%ah, %ah	/* Is it NUL?.  */
> -	jz	4f		/* yes, finish.  */
> -	incq	%rdi		/* Increment destination.  */
> -	shrq	$16, %rax	/* Shift...  */
> -	jmp	3b		/* and look at next two bytes in %rax.  */
> -
> -51:
> -	/* Search the bytes directly, checking for overflows.  */
> -	incq	%rsi
> -	incq	%rdi
> -	decq	%rdx
> -	jz	HIDDEN_JUMPTARGET (__chk_fail)
> -52:
> -	movb	(%rsi), %al	/* Fetch a byte */
> -	testb	%al, %al	/* Is it NUL? */
> -	movb	%al, (%rdi)	/* Store it */
> -	jnz	51b		/* If it was NUL, done! */
> -4:
> -#ifdef USE_AS_STPCPY_CHK
> -	movq	%rdi, %rax	/* Destination is return value.  */
> -#else
> -	movq	%r10, %rax	/* Source is return value.  */
> -#endif
> -	retq
> -
> -50:
> -	testq	%rdx, %rdx
> -	jnz	52b
> -	jmp	HIDDEN_JUMPTARGET (__chk_fail)
> -
> -END (STRCPY_CHK)


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