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[Bug libc/16629] [aarch64] setcontext clobbers alternate signal stack
- From: "cvs-commit at gcc dot gnu.org" <sourceware-bugzilla at sourceware dot org>
- To: glibc-bugs at sourceware dot org
- Date: Thu, 17 Apr 2014 10:41:41 +0000
- Subject: [Bug libc/16629] [aarch64] setcontext clobbers alternate signal stack
- Auto-submitted: auto-generated
- References: <bug-16629-131 at http dot sourceware dot org/bugzilla/>
https://sourceware.org/bugzilla/show_bug.cgi?id=16629
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- Log -----------------------------------------------------------------
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=7c6776620db8e48fca492dbcac88d1c0f239dcde
commit 7c6776620db8e48fca492dbcac88d1c0f239dcde
Author: Will Newton <will.newton@linaro.org>
Date: Thu Mar 13 09:45:29 2014 +0000
manual/setjmp.texi: Clarify setcontext and signal handlers text
Calling setcontext from a signal handler can be done safely so
it is sufficient to note that it is not recommended.
Also mention in setcontext documentation that the behaviour of
setcontext when restoring a context created by a call to a signal
handler is unspecified.
2014-04-17 Will Newton <will.newton@linaro.org>
* manual/setjmp.texi (System V contexts): Add note that
calling setcontext on a context created by a call to a
signal handler is undefined. Update text to note that
setcontext from a signal handler is possible but not
recommended.
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=e04a4e9d2e639a7770e1c0d24ecbcf92abf6bba8
commit e04a4e9d2e639a7770e1c0d24ecbcf92abf6bba8
Author: Will Newton <will.newton@linaro.org>
Date: Tue Feb 25 14:29:32 2014 +0000
stdlib/tst-setcontext.c: Check for clobbering of signal stack
On aarch64 calling swapcontext clobbers the state of the signal
stack (BZ #16629). Check that the address and size of the signal
stack before and after the call to swapcontext remains the same.
ChangeLog:
2014-04-17 Will Newton <will.newton@linaro.org>
[BZ #16629]
* stdlib/tst-setcontext.c: Include signal.h.
(main): Check that the signal stack before and
after swapcontext is the same.
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=37d350073888887637aa67dddf988d9c4b226032
commit 37d350073888887637aa67dddf988d9c4b226032
Author: Will Newton <will.newton@linaro.org>
Date: Wed Mar 12 16:14:51 2014 +0000
aarch64: Re-implement setcontext without rt_sigreturn syscall
The current implementation of setcontext uses rt_sigreturn to restore
the contents of registers. This contrasts with the way most other
architectures implement setcontext:
powerpc64, mips, tile:
Call rt_sigreturn if context was created by a call to a signal handler,
otherwise restore in user code.
powerpc32:
Call swapcontext system call and don't call sigreturn or rt_sigreturn.
x86_64, sparc, hppa, sh, ia64, m68k, s390, arm:
Only support restoring "synchronous" contexts, that is contexts
created by getcontext, and restoring in user code and don't call
sigreturn or rt_sigreturn.
alpha:
Call sigreturn (but not rt_sigreturn) in all cases to do the restore.
The text of the setcontext manpage suggests that the requirement to be
able to restore a signal handler created context has been dropped from
SUSv2:
If the context was obtained by a call to a signal handler, then old
standard text says that "program execution continues with the program
instruction following the instruction interrupted by the signal".
However, this sentence was removed in SUSv2, and the present verdict
is "the result is unspecified".
Implementing setcontext by calling rt_sigreturn unconditionally causes
problems when used with sigaltstack as in BZ #16629. On this basis it
seems that aarch64 is broken and that new ports should only support
restoring contexts created with getcontext and do not need to call
rt_sigreturn at all.
This patch re-implements the aarch64 setcontext function to restore
the context in user code in a similar manner to x86_64 and other ports.
ChangeLog:
2014-04-17 Will Newton <will.newton@linaro.org>
[BZ #16629]
* sysdeps/unix/sysv/linux/aarch64/setcontext.S (__setcontext):
Re-implement to restore registers in user code and avoid
rt_sigreturn system call.
-----------------------------------------------------------------------
Summary of changes:
ChangeLog | 17 +++
NEWS | 10 +-
manual/setjmp.texi | 19 ++--
stdlib/tst-setcontext.c | 21 ++++
sysdeps/unix/sysv/linux/aarch64/setcontext.S | 150 ++++++++++++++++----------
5 files changed, 149 insertions(+), 68 deletions(-)
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