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authorCarl Shaw <carl.shaw@st.com>2009-08-24 15:07:08 +0900
committerPaul Mundt <lethal@linux-sh.org>2009-08-24 15:07:08 +0900
commit2fc742f8d64c68b4a175a1dcb28351b112d63315 (patch)
treed49512af5019d3ecdfddd96f9f2a0398184f352b /arch/sh/include/asm
parent5a0ab35e43a6e3c69893c0091fe6a78ea8b3e443 (diff)
sh: Improve unwind info for signals
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>
Diffstat (limited to 'arch/sh/include/asm')
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