[01/13] posix: Consolidate Linux pause syscall

Message ID 1494611894-9282-1-git-send-email-adhemerval.zanella@linaro.org
State New
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  • [01/13] posix: Consolidate Linux pause syscall
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Adhemerval Zanella May 12, 2017, 5:58 p.m.
This patch consolidates the pause Linux implementation on
sysdeps/unix/sysv/linux/pause.c.  If defined the pause syscall
(__NR_pause) will be used, other ppoll with 0 arguments will be
used instead.

It has the small advantage of generic pause implementation with
uses rt_sigprocmask plus rt_sigsuspend because it requires only
one syscall and the pause is done atomically regarding signal
handling (for instance, pause may not be interrupted if the
signal arrives between the rt_sigprocmask and rt_sigsuspend
syscall).

Checked on i686-linux-gnu, x86_64-linux-gnu, x86_64-linux-gnux32,
arch64-linux-gnu, arm-linux-gnueabihf, powerpc64le-linux-gnu,
sparc64-linux-gnu, and sparcv9-linux-gnu.

	* sysdeps/unix/sysv/linux/generic/pause.c: Remove file.
	* sysdeps/unix/sysv/linux/sparc/sparc64/pause.c: Likewise.
	* sysdeps/unix/sysv/linux/sparc/kernel-features.h [__arch64__]
	(__NR_pause): Undefine.
	* sysdeps/unix/sysv/linux/pause.c: New file.
	* sysdeps/unix/sysv/linux/syscalls.list: Remove pause from
	auto-generation list.
---
 ChangeLog                                       | 10 ++++++++++
 sysdeps/unix/sysv/linux/{generic => }/pause.c   | 18 +++++++-----------
 sysdeps/unix/sysv/linux/sparc/kernel-features.h |  6 ++++++
 sysdeps/unix/sysv/linux/sparc/sparc64/pause.c   |  9 ---------
 sysdeps/unix/sysv/linux/syscalls.list           |  1 -
 5 files changed, 23 insertions(+), 21 deletions(-)
 rename sysdeps/unix/sysv/linux/{generic => }/pause.c (75%)
 delete mode 100644 sysdeps/unix/sysv/linux/sparc/sparc64/pause.c

-- 
2.7.4

Comments

Florian Weimer May 12, 2017, 6:15 p.m. | #1
On 05/12/2017 07:58 PM, Adhemerval Zanella wrote:
> +/* sparc64 defines __NR_pause,  however it is not supported (ENOSYS).

> +   Undefine so pause.c can use a correct alternative.  */

> +# ifdef __NR_pause

> +#  undef __NR_pause

> +# endif


I think you can #undef unconditionally, there isn't a warning for that.

+  return SYSCALL_CANCEL (ppoll, 0, 0, 0, 0, 0);

I think some of the arguments should be NULL instead of 0.

I'm not completely sure if an empty ppoll without a timeout has the 
required semantics, but I can't think of a reason why it would not work.

Thanks,
Florian
Adhemerval Zanella May 12, 2017, 6:41 p.m. | #2
On 12/05/2017 15:15, Florian Weimer wrote:
> On 05/12/2017 07:58 PM, Adhemerval Zanella wrote:

>> +/* sparc64 defines __NR_pause,  however it is not supported (ENOSYS).

>> +   Undefine so pause.c can use a correct alternative.  */

>> +# ifdef __NR_pause

>> +#  undef __NR_pause

>> +# endif

> 

> I think you can #undef unconditionally, there isn't a warning for that.


Alright, I will change it.

> 

> +  return SYSCALL_CANCEL (ppoll, 0, 0, 0, 0, 0);

> 

> I think some of the arguments should be NULL instead of 0.


I will change to SYSCALL_CANCEL (ppoll, NULL, 0, NULL, NULL).

> 

> I'm not completely sure if an empty ppoll without a timeout has the required semantics, but I can't think of a reason why it would not work.


I though about Linux syscall with similar semantics regarding signals,
but I couldn't find one.

Patch hide | download patch | download mbox

diff --git a/sysdeps/unix/sysv/linux/generic/pause.c b/sysdeps/unix/sysv/linux/pause.c
similarity index 75%
rename from sysdeps/unix/sysv/linux/generic/pause.c
rename to sysdeps/unix/sysv/linux/pause.c
index a8b3e33..c6b252a 100644
--- a/sysdeps/unix/sysv/linux/generic/pause.c
+++ b/sysdeps/unix/sysv/linux/pause.c
@@ -1,6 +1,6 @@ 
-/* Copyright (C) 2011-2017 Free Software Foundation, Inc.
+/* Linux pause syscall implementation.
+   Copyright (C) 2017 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
-   Contributed by Chris Metcalf <cmetcalf@tilera.com>, 2011.
 
    The GNU C Library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Lesser General Public
@@ -26,14 +26,10 @@ 
 int
 __libc_pause (void)
 {
-  sigset_t set;
-
-  int rc =
-    SYSCALL_CANCEL (rt_sigprocmask, SIG_BLOCK, NULL, &set, _NSIG / 8);
-  if (rc == 0)
-    rc = SYSCALL_CANCEL (rt_sigsuspend, &set, _NSIG / 8);
-
-  return rc;
+#ifdef __NR_pause
+  return SYSCALL_CANCEL (pause);
+#else
+  return SYSCALL_CANCEL (ppoll, 0, 0, 0, 0, 0);
+#endif
 }
-
 weak_alias (__libc_pause, pause)
diff --git a/sysdeps/unix/sysv/linux/sparc/kernel-features.h b/sysdeps/unix/sysv/linux/sparc/kernel-features.h
index 72065a0..dd9108b 100644
--- a/sysdeps/unix/sysv/linux/sparc/kernel-features.h
+++ b/sysdeps/unix/sysv/linux/sparc/kernel-features.h
@@ -32,6 +32,12 @@ 
 # undef __ASSUME_ACCEPT_SYSCALL
 # undef __ASSUME_CONNECT_SYSCALL
 # undef __ASSUME_RECVFROM_SYSCALL
+#else
+/* sparc64 defines __NR_pause,  however it is not supported (ENOSYS).
+   Undefine so pause.c can use a correct alternative.  */
+# ifdef __NR_pause
+#  undef __NR_pause
+# endif
 #endif
 
 /* sparc only supports ipc syscall.  */
diff --git a/sysdeps/unix/sysv/linux/sparc/sparc64/pause.c b/sysdeps/unix/sysv/linux/sparc/sparc64/pause.c
deleted file mode 100644
index e399e7c..0000000
--- a/sysdeps/unix/sysv/linux/sparc/sparc64/pause.c
+++ /dev/null
@@ -1,9 +0,0 @@ 
-#include <errno.h>
-#include <signal.h>
-#include <unistd.h>
-#include <sysdep-cancel.h>
-
-#define __sigprocmask(how, set, oset) \
-  INLINE_SYSCALL (rt_sigprocmask, 4, how, set, oset, _NSIG / 8)
-
-#include <sysdeps/posix/pause.c>
diff --git a/sysdeps/unix/sysv/linux/syscalls.list b/sysdeps/unix/sysv/linux/syscalls.list
index f4abf3e..eab30dd 100644
--- a/sysdeps/unix/sysv/linux/syscalls.list
+++ b/sysdeps/unix/sysv/linux/syscalls.list
@@ -44,7 +44,6 @@  munlock		-	munlock		i:ai	munlock
 munlockall	-	munlockall	i:	munlockall
 nanosleep	-	nanosleep	Ci:pp	__nanosleep	nanosleep
 nfsservctl	EXTRA	nfsservctl	i:ipp	nfsservctl
-pause		-	pause		Ci:	__libc_pause	pause
 pipe		-	pipe		i:f	__pipe		pipe
 pipe2		-	pipe2		i:fi	__pipe2		pipe2
 pivot_root	EXTRA	pivot_root	i:ss	pivot_root