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Re: [PATCH] Avoid reading errno in syscall implementations
- From: "H.J. Lu" <hjl dot tools at gmail dot com>
- To: Joseph Myers <joseph at codesourcery dot com>
- Cc: GNU C Library <libc-alpha at sourceware dot org>
- Date: Mon, 19 Oct 2015 10:49:17 -0700
- Subject: Re: [PATCH] Avoid reading errno in syscall implementations
- Authentication-results: sourceware.org; auth=none
- References: <20151019164832 dot GA28619 at intel dot com> <alpine dot DEB dot 2 dot 10 dot 1510191653500 dot 23235 at digraph dot polyomino dot org dot uk>
On Mon, Oct 19, 2015 at 10:00 AM, Joseph Myers <joseph@codesourcery.com> wrote:
> On Mon, 19 Oct 2015, H.J. Lu wrote:
>
>> Reading errno is expensive for x86 PIC. With INTERNAL_SYSCALL,
>> INTERNAL_SYSCALL_ERROR_P, INTERNAL_SYSCALL_ERRNO and
>> INLINE_SYSCALL_ERROR_RETURN_VALUE, we can avoid reading errno.
>
> I don't follow how this patch works. How do you ensure that in the cases
> where there is an error that is not ENOSYS, errno does get set as it would
> have been before?
>
>> - int res = INLINE_SYSCALL (eventfd2, 2, count, flags);
>> # ifndef __ASSUME_EVENTFD2
>> - if (res != -1 || errno != ENOSYS)
>> -# endif
>> + INTERNAL_SYSCALL_DECL (err);
>> + int res = INTERNAL_SYSCALL (eventfd2, err, 2, count, flags);
>> + if (!__glibc_unlikely (INTERNAL_SYSCALL_ERROR_P (res, err))
>> + || INTERNAL_SYSCALL_ERRNO (res, err) != ENOSYS)
>> return res;
>
> E.g. this appears to be semantically different from the previous code -
> the previous code would have set errno here from a non-ENOSYS error, and
> the new code wouldn't.
>
> (__ASSUME_EVENTFD2 is always defined except on alpha. Presumably your "no
> code changes" was because code paths used on x86_64 didn't get changed by
> the patch.)
Here is the updated patch. Only getrlimit64.os and setrlimit64.os
are changed on i686. OK for master?
Thanks.
--
H.J.
From 6f6e3ee567cbff328df83dcf9ee0a5459746fce0 Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.tools@gmail.com>
Date: Fri, 21 Aug 2015 14:46:05 -0700
Subject: [PATCH] Avoid reading errno in syscall implementations
Reading errno is expensive for x86 PIC. With INTERNAL_SYSCALL,
INTERNAL_SYSCALL_ERROR_P, INTERNAL_SYSCALL_ERRNO and
INLINE_SYSCALL_ERROR_RETURN_VALUE, we can avoid reading errno.
There are no code changes on x86-64. On i686, libc.so sizes in bytes
show:
text data bss dec
after 1748495 11380 11132 1771007
before 1748403 11380 11132 1770915
* sysdeps/unix/sysv/linux/eventfd.c (eventfd): Use
INTERNAL_SYSCALL, INTERNAL_SYSCALL_ERROR_P and
INTERNAL_SYSCALL_ERRNO to avoid reading errno.
* sysdeps/unix/sysv/linux/fstatfs64.c (__fstatfs64): Likewise.
* sysdeps/unix/sysv/linux/getrlimit64.c (__getrlimit64):
Likewise.
* sysdeps/unix/sysv/linux/setrlimit64.c (setrlimit64):
Likewise.
* sysdeps/unix/sysv/linux/signalfd.c (signalfd): Likewise.
* sysdeps/unix/sysv/linux/statfs64.c (__statfs64): Likewise.
---
sysdeps/unix/sysv/linux/eventfd.c | 11 ++++++++---
sysdeps/unix/sysv/linux/fstatfs64.c | 13 +++++++++----
sysdeps/unix/sysv/linux/getrlimit64.c | 8 ++++++--
sysdeps/unix/sysv/linux/lxstat64.c | 7 +++++--
sysdeps/unix/sysv/linux/setrlimit64.c | 8 ++++++--
sysdeps/unix/sysv/linux/signalfd.c | 12 +++++++++---
sysdeps/unix/sysv/linux/statfs64.c | 14 ++++++++++----
7 files changed, 53 insertions(+), 20 deletions(-)
diff --git a/sysdeps/unix/sysv/linux/eventfd.c b/sysdeps/unix/sysv/linux/eventfd.c
index efce282..3a91781 100644
--- a/sysdeps/unix/sysv/linux/eventfd.c
+++ b/sysdeps/unix/sysv/linux/eventfd.c
@@ -25,11 +25,16 @@ int
eventfd (unsigned int count, int flags)
{
#ifdef __NR_eventfd2
- int res = INLINE_SYSCALL (eventfd2, 2, count, flags);
# ifndef __ASSUME_EVENTFD2
- if (res != -1 || errno != ENOSYS)
-# endif
+ INTERNAL_SYSCALL_DECL (err);
+ int res = INTERNAL_SYSCALL (eventfd2, err, 2, count, flags);
+ if (!__glibc_unlikely (INTERNAL_SYSCALL_ERROR_P (res, err)))
return res;
+ else if (INTERNAL_SYSCALL_ERRNO (res, err) != ENOSYS)
+ return INLINE_SYSCALL_ERROR_RETURN_VALUE (INTERNAL_SYSCALL_ERRNO (res, err));
+# else
+ return INLINE_SYSCALL (eventfd2, 2, count, flags);
+# endif
#endif
#ifndef __ASSUME_EVENTFD2
diff --git a/sysdeps/unix/sysv/linux/fstatfs64.c b/sysdeps/unix/sysv/linux/fstatfs64.c
index af83830..819b623 100644
--- a/sysdeps/unix/sysv/linux/fstatfs64.c
+++ b/sysdeps/unix/sysv/linux/fstatfs64.c
@@ -35,12 +35,17 @@ __fstatfs64 (int fd, struct statfs64 *buf)
if (! __no_statfs64)
# endif
{
- int result = INLINE_SYSCALL (fstatfs64, 3, fd, sizeof (*buf), buf);
-
# if __ASSUME_STATFS64 == 0
- if (result == 0 || errno != ENOSYS)
-# endif
+ INTERNAL_SYSCALL_DECL (err);
+ int result = INTERNAL_SYSCALL (fstatfs64, err, 3, fd,
+ sizeof (*buf), buf);
+ if (!__glibc_unlikely (INTERNAL_SYSCALL_ERROR_P (result, err)))
return result;
+ else if (INTERNAL_SYSCALL_ERRNO (result, err) != ENOSYS)
+ return INLINE_SYSCALL_ERROR_RETURN_VALUE (INTERNAL_SYSCALL_ERRNO (result, err));
+# else
+ return INLINE_SYSCALL (fstatfs64, 3, fd, sizeof (*buf), buf);
+# endif
# if __ASSUME_STATFS64 == 0
__no_statfs64 = 1;
diff --git a/sysdeps/unix/sysv/linux/getrlimit64.c b/sysdeps/unix/sysv/linux/getrlimit64.c
index 100ba62..bc36c14 100644
--- a/sysdeps/unix/sysv/linux/getrlimit64.c
+++ b/sysdeps/unix/sysv/linux/getrlimit64.c
@@ -30,9 +30,13 @@ __getrlimit64 (enum __rlimit_resource resource, struct rlimit64 *rlimits)
return INLINE_SYSCALL (prlimit64, 4, 0, resource, NULL, rlimits);
#else
# ifdef __NR_prlimit64
- int res = INLINE_SYSCALL (prlimit64, 4, 0, resource, NULL, rlimits);
- if (res == 0 || errno != ENOSYS)
+ INTERNAL_SYSCALL_DECL (err);
+ int res = INTERNAL_SYSCALL (prlimit64, err, 4, 0, resource, NULL,
+ rlimits);
+ if (!__glibc_unlikely (INTERNAL_SYSCALL_ERROR_P (res, err)))
return res;
+ else if (INTERNAL_SYSCALL_ERRNO (res, err) != ENOSYS)
+ return INLINE_SYSCALL_ERROR_RETURN_VALUE (INTERNAL_SYSCALL_ERRNO (res, err));
# endif
struct rlimit rlimits32;
diff --git a/sysdeps/unix/sysv/linux/lxstat64.c b/sysdeps/unix/sysv/linux/lxstat64.c
index 5d0c051..63959cf 100644
--- a/sysdeps/unix/sysv/linux/lxstat64.c
+++ b/sysdeps/unix/sysv/linux/lxstat64.c
@@ -30,8 +30,11 @@
int
___lxstat64 (int vers, const char *name, struct stat64 *buf)
{
- int result;
- result = INLINE_SYSCALL (lstat64, 2, name, buf);
+ INTERNAL_SYSCALL_DECL (err);
+ int result = INTERNAL_SYSCALL (lstat64, err, 2, name, buf);
+ if (__glibc_unlikely (INTERNAL_SYSCALL_ERROR_P (result, err)))
+ return INLINE_SYSCALL_ERROR_RETURN_VALUE (INTERNAL_SYSCALL_ERRNO (result,
+ err));
#if defined _HAVE_STAT64___ST_INO && __ASSUME_ST_INO_64_BIT == 0
if (__builtin_expect (!result, 1) && buf->__st_ino != (__ino_t) buf->st_ino)
buf->st_ino = buf->__st_ino;
diff --git a/sysdeps/unix/sysv/linux/setrlimit64.c b/sysdeps/unix/sysv/linux/setrlimit64.c
index 5b1f657..b13014a 100644
--- a/sysdeps/unix/sysv/linux/setrlimit64.c
+++ b/sysdeps/unix/sysv/linux/setrlimit64.c
@@ -31,9 +31,13 @@ setrlimit64 (enum __rlimit_resource resource, const struct rlimit64 *rlimits)
return INLINE_SYSCALL (prlimit64, 4, 0, resource, rlimits, NULL);
#else
# ifdef __NR_prlimit64
- int res = INLINE_SYSCALL (prlimit64, 4, 0, resource, rlimits, NULL);
- if (res == 0 || errno != ENOSYS)
+ INTERNAL_SYSCALL_DECL (err);
+ int res = INTERNAL_SYSCALL (prlimit64, err, 4, 0, resource, rlimits,
+ NULL);
+ if (!__glibc_unlikely (INTERNAL_SYSCALL_ERROR_P (res, err)))
return res;
+ else if (INTERNAL_SYSCALL_ERRNO (res, err) != ENOSYS)
+ return INLINE_SYSCALL_ERROR_RETURN_VALUE (INTERNAL_SYSCALL_ERRNO (res, err));
# endif
struct rlimit rlimits32;
diff --git a/sysdeps/unix/sysv/linux/signalfd.c b/sysdeps/unix/sysv/linux/signalfd.c
index 8573450..95a9707 100644
--- a/sysdeps/unix/sysv/linux/signalfd.c
+++ b/sysdeps/unix/sysv/linux/signalfd.c
@@ -26,11 +26,17 @@ int
signalfd (int fd, const sigset_t *mask, int flags)
{
#ifdef __NR_signalfd4
- int res = INLINE_SYSCALL (signalfd4, 4, fd, mask, _NSIG / 8, flags);
# ifndef __ASSUME_SIGNALFD4
- if (res != -1 || errno != ENOSYS)
-# endif
+ INTERNAL_SYSCALL_DECL (err);
+ int res = INTERNAL_SYSCALL (signalfd4, err, 4, fd, mask, _NSIG / 8,
+ flags);
+ if (!__glibc_unlikely (INTERNAL_SYSCALL_ERROR_P (res, err)))
return res;
+ else if (INTERNAL_SYSCALL_ERRNO (res, err) != ENOSYS)
+ return INLINE_SYSCALL_ERROR_RETURN_VALUE (INTERNAL_SYSCALL_ERRNO (res, err));
+# else
+ return INLINE_SYSCALL (signalfd4, 4, fd, mask, _NSIG / 8, flags);
+# endif
#endif
#ifndef __ASSUME_SIGNALFD4
diff --git a/sysdeps/unix/sysv/linux/statfs64.c b/sysdeps/unix/sysv/linux/statfs64.c
index ac5c33f..469eda1 100644
--- a/sysdeps/unix/sysv/linux/statfs64.c
+++ b/sysdeps/unix/sysv/linux/statfs64.c
@@ -37,12 +37,18 @@ __statfs64 (const char *file, struct statfs64 *buf)
if (! __no_statfs64)
# endif
{
- int result = INLINE_SYSCALL (statfs64, 3, file, sizeof (*buf), buf);
-
# if __ASSUME_STATFS64 == 0
- if (result == 0 || errno != ENOSYS)
-# endif
+ INTERNAL_SYSCALL_DECL (err);
+ int result = INTERNAL_SYSCALL (statfs64, err, 3, file,
+ sizeof (*buf), buf);
+
+ if (!__glibc_unlikely (INTERNAL_SYSCALL_ERROR_P (result, err)))
return result;
+ else if (INTERNAL_SYSCALL_ERRNO (result, err) != ENOSYS)
+ return INLINE_SYSCALL_ERROR_RETURN_VALUE (INTERNAL_SYSCALL_ERRNO (result, err));
+# else
+ return INLINE_SYSCALL (statfs64, 3, file, sizeof (*buf), buf);
+# endif
# if __ASSUME_STATFS64 == 0
__no_statfs64 = 1;
--
2.4.3