GCC does not issue unwind information for function epilogues.
Unfortunately we can catch a signal during an epilogue. The signal
handler writes the current context and signal return code onto the stack
overwriting previous contents. During unwinding, libgcc can try to
restore registers from the stack and restores corrupted ones. This can
lead to segmentation, misaligned access and sigbus faults.
For example, consider the following code:
mov.l r12,@-r15
mov.l r14,@-r15
sts.l pr,@-r15
mov r15,r14
<do stuff>
mov r14, r15
lds.l @r15+, pr
<<< SIGNAL HERE
mov.l @r15+, r14
mov.l @r15+, r12
rts
Unwind is aware that pr was pushed to stack in prolog, so tries to
restore it. Unfortunately it restores the last word of the signal
handler code placed on the stack by the kernel.
This patch tries to avoid the problem by adding a guard region on the
stack between where the function pushes data and where the signal handler
pushes its return code. We probably don't see this problem often because
exception handling unwinding in an epilogue only occurs due to a pthread
cancel signal. Also the kernel signal stack handler alignment of 8 bytes
could hide the occurance of this problem sometimes as the stack may not
be trampled at a particular required word.
This is not guaranteed to always work. It relies on a frame pointer
existing for the function (so it can get the correct sp value) which is
not always the case for the SH4.
Modifications will also be made to libgcc for the case where there is no
fp.
Signed-off-by: Carl Shaw <carl.shaw@st.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>
GCC 4.5.0 complains about the declaration of variables
__kernel_sigreturn and __kernel_rt_sigreturn because they have type
void. Correctly declare these symbols as functions to fix the
following error,
arch/sh/kernel/signal_32.c: In function 'setup_frame':
arch/sh/kernel/signal_32.c:368:14: error: taking address of expression of type 'void'
arch/sh/kernel/signal_32.c: In function 'setup_rt_frame':
arch/sh/kernel/signal_32.c:452:14: error: taking address of expression of type 'void'
make[1]: *** [arch/sh/kernel/signal_32.o] Error 1
make: *** [arch/sh/kernel] Error 2
Signed-off-by: Matt Fleming <matt@console-pimps.org>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>
The T-bit manipulation for syscall error checking had the side effect of
spuriously returning ERESTART* errno values over EINTR. So, we simplify
the error checking a bit and leave the T-bit alone.
Reported-by: Kaz Kojima <kkojima@rr.iij4u.or.jp>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>
This follows the changes in commits:
7d6d637dac4f72c4279e
on powerpc. Adding in TIF_NOTIFY_RESUME, and cleaning up the syscall
tracing to be more generic. This is an incremental step to turning
on tracehook, as well as unifying more of the ptrace and signal code
across the 32/64 split.
Signed-off-by: Paul Mundt <lethal@linux-sh.org>
The current kernel behaviour is to reenable interrupts unconditionally
when taking a page fault. This patch changes this to only enable them
if interrupts were previously enabled.
It also fixes a problem seen with this fix in place: the kernel previously
flushed the vsyscall page when handling a signal, which is not only
unncessary, but caused a possible sleep with interrupts disabled.
Signed-off-by: Stuart Menefy <stuart.menefy@st.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>
Add implementation of flush_icache_range() suitable for signal handler
and kprobes. Remove flush_cache_sigtramp() and change signal.c to use
flush_icache_range().
Signed-off-by: Chris Smith <chris.smith@st.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>
Presently with preempt enabled there's the possibility to be preempted
after the TIF_USEDFPU test and the register save, leading to bogus
state post-__switch_to(). Use an explicit preempt_disable()/enable()
pair around unlazy_fpu()/clear_fpu() to avoid this. Follows the x86
change.
Reported-by: Takuo Koguchi <takuo.koguchi.sw@hitachi.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>
This implements kernel-level atomic rollback built on top of gUSA,
as an alternative non-IRQ based atomicity method. This is generally
a faster method for platforms that are lacking the LL/SC pairs that
SH-4A and later use, and is only supportable on legacy cores.
Signed-off-by: Stuart Menefy <stuart.menefy@st.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>
