From e306dfd06fcb44d21c80acb8e5a88d55f3d1cf63 Mon Sep 17 00:00:00 2001 From: Olof Johansson Date: Fri, 14 Feb 2014 19:35:15 +0000 Subject: [PATCH] ARM64: unwind: Fix PC calculation The frame PC value in the unwind code used to just take the saved LR value and use that. That's incorrect as a stack trace, since it shows the return path stack, not the call path stack. In particular, it shows faulty information in case the bl is done as the very last instruction of one label, since the return point will be in the next label. That can easily be seen with tail calls to panic(), which is marked __noreturn and thus doesn't have anything useful after it. Easiest here is to just correct the unwind code and do a -4, to get the actual call site for the backtrace instead of the return site. Signed-off-by: Olof Johansson Cc: stable@vger.kernel.org Signed-off-by: Catalin Marinas --- arch/arm64/kernel/stacktrace.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c index c3b6c63ea5fb..38f0558f0c0a 100644 --- a/arch/arm64/kernel/stacktrace.c +++ b/arch/arm64/kernel/stacktrace.c @@ -48,7 +48,11 @@ int unwind_frame(struct stackframe *frame) frame->sp = fp + 0x10; frame->fp = *(unsigned long *)(fp); - frame->pc = *(unsigned long *)(fp + 8); + /* + * -4 here because we care about the PC at time of bl, + * not where the return will go. + */ + frame->pc = *(unsigned long *)(fp + 8) - 4; return 0; } -- 2.20.1