| Message ID | 1494611894-9282-3-git-send-email-adhemerval.zanella@linaro.org |
|---|---|
| State | New |
| Headers | show |
| Series | [01/13] posix: Consolidate Linux pause syscall | expand |
On 05/12/2017 07:58 PM, Adhemerval Zanella wrote: > +++ b/nptl/Makefile > +CFLAGS-nanosleep.c = -fexceptions -fasynchronous-unwind-tables > +++ b/posix/Makefile > +CFLAGS-nanosleep.c = -fexceptions Why the discrepancy? I suppose both implementations could be called in a multi-threaded program. Thanks, Florian
On 12/05/2017 15:21, Florian Weimer wrote: > On 05/12/2017 07:58 PM, Adhemerval Zanella wrote: >> +++ b/nptl/Makefile > >> +CFLAGS-nanosleep.c = -fexceptions -fasynchronous-unwind-tables > > >> +++ b/posix/Makefile > >> +CFLAGS-nanosleep.c = -fexceptions > > Why the discrepancy? I suppose both implementations could be called in a multi-threaded program. I do not recall a reason why these are different, I will set both to -fexceptions -fasynchronous-unwind-tables. AFAIK -fexception is the required flag for cancelable syscall to work correctly, while -fasynchronous-unwind-tables is make it work also through signals (not really sure though). So I would say to be safe we should set both.
On Mon, 15 May 2017, Florian Weimer wrote: > Technically, __gcc_personality_v0 is part of the ABI, so there could still be > user code out there that uses it. And of course, Ada and C++ code which is > called from glibc code (or which runs from a signal handler that interrupts > glibc code) could have stack frames with crucial unwinding information when > thread cancellation happens. > > In order to reach those stack frames, the cancellation code needs to unwind > through glibc code. This could be any code in glibc which calls a function > which is a cancellation point. > > Based on that, I think we should compile all of glibc with unwinding support, > and considering that asynchronous cancellation can happen through synchronous > cancellation within signal handlers, we need both -fexceptions *and* > -fasynchronous-unwind-tables. See <https://sourceware.org/ml/libc-alpha/2015-10/msg00569.html> and followups for discussion of the circumstances when those options may be needed. -- Joseph S. Myers joseph@codesourcery.com
On 05/15/2017 01:36 PM, Joseph Myers wrote: > See <https://sourceware.org/ml/libc-alpha/2015-10/msg00569.html> and > followups for discussion of the circumstances when those options may be > needed. Interesting. So the C frontend can actually generate code which invokes the personality routine (via the cleanup attribute). I wonder if we can use this to make cancellation safer, at least within glibc. Florian
diff --git a/nptl/Makefile b/nptl/Makefile index d39bb50..cdf69bd 100644 --- a/nptl/Makefile +++ b/nptl/Makefile @@ -216,6 +216,7 @@ CFLAGS-sendmsg.c = -fexceptions -fasynchronous-unwind-tables CFLAGS-close.c = -fexceptions -fasynchronous-unwind-tables CFLAGS-read.c = -fexceptions -fasynchronous-unwind-tables CFLAGS-write.c = -fexceptions -fasynchronous-unwind-tables +CFLAGS-nanosleep.c = -fexceptions -fasynchronous-unwind-tables CFLAGS-pt-system.c = -fexceptions diff --git a/posix/Makefile b/posix/Makefile index 0025d8a..9f186cd 100644 --- a/posix/Makefile +++ b/posix/Makefile @@ -232,6 +232,7 @@ CFLAGS-execle.os = -fomit-frame-pointer CFLAGS-execl.os = -fomit-frame-pointer CFLAGS-execvp.os = -fomit-frame-pointer CFLAGS-execlp.os = -fomit-frame-pointer +CFLAGS-nanosleep.c = -fexceptions tstgetopt-ARGS = -a -b -cfoobar --required foobar --optional=bazbug \ --none random --col --color --colour diff --git a/sysdeps/unix/sysv/linux/nanosleep.c b/sysdeps/unix/sysv/linux/nanosleep.c new file mode 100644 index 0000000..b352f84 --- /dev/null +++ b/sysdeps/unix/sysv/linux/nanosleep.c @@ -0,0 +1,30 @@ +/* Linux high resolution nanosleep implementation. + Copyright (C) 2017 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 + 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 <time.h> +#include <sysdep-cancel.h> + +/* Pause execution for a number of nanoseconds. */ +int +__nanosleep (const struct timespec *requested_time, + struct timespec *remaining) +{ + return SYSCALL_CANCEL (nanosleep, requested_time, remaining); +} +libc_hidden_def (__nanosleep) +weak_alias (__nanosleep, nanosleep) diff --git a/sysdeps/unix/sysv/linux/syscalls.list b/sysdeps/unix/sysv/linux/syscalls.list index eab30dd..7fca6f8 100644 --- a/sysdeps/unix/sysv/linux/syscalls.list +++ b/sysdeps/unix/sysv/linux/syscalls.list @@ -42,7 +42,6 @@ mount EXTRA mount i:sssip __mount mount mremap EXTRA mremap b:ainip __mremap mremap munlock - munlock i:ai munlock munlockall - munlockall i: munlockall -nanosleep - nanosleep Ci:pp __nanosleep nanosleep nfsservctl EXTRA nfsservctl i:ipp nfsservctl pipe - pipe i:f __pipe pipe pipe2 - pipe2 i:fi __pipe2 pipe2