Since clang does not push pc and sp in function prologues, the current implementation of unwind_frame does not work. By using the previous frame's lr/fp instead of saved pc/sp we get valid unwinds on clang-built kernels. The bounds check on next frame pointer must be changed as well since there are 8 less bytes between frames. This fixes /proc/<pid>/stack. Link: https://github.com/ClangBuiltLinux/linux/issues/912 Reported-by: Miles Chen <miles.chen@xxxxxxxxxxxx> Tested-by: Miles Chen <miles.chen@xxxxxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> Signed-off-by: Nathan Huckleberry <nhuck@xxxxxxxxxx> --- arch/arm/kernel/stacktrace.c | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) diff --git a/arch/arm/kernel/stacktrace.c b/arch/arm/kernel/stacktrace.c index cc726afea023..76ea4178a55c 100644 --- a/arch/arm/kernel/stacktrace.c +++ b/arch/arm/kernel/stacktrace.c @@ -22,6 +22,19 @@ * A simple function epilogue looks like this: * ldm sp, {fp, sp, pc} * + * When compiled with clang, pc and sp are not pushed. A simple function + * prologue looks like this when built with clang: + * + * stmdb {..., fp, lr} + * add fp, sp, #x + * sub sp, sp, #y + * + * A simple function epilogue looks like this when built with clang: + * + * sub sp, fp, #x + * ldm {..., fp, pc} + * + * * Note that with framepointer enabled, even the leaf functions have the same * prologue and epilogue, therefore we can ignore the LR value in this case. */ @@ -34,6 +47,16 @@ int notrace unwind_frame(struct stackframe *frame) low = frame->sp; high = ALIGN(low, THREAD_SIZE); +#ifdef CONFIG_CC_IS_CLANG + /* check current frame pointer is within bounds */ + if (fp < low + 4 || fp > high - 4) + return -EINVAL; + + frame->sp = frame->fp; + frame->fp = *(unsigned long *)(fp); + frame->pc = frame->lr; + frame->lr = *(unsigned long *)(fp + 4); +#else /* check current frame pointer is within bounds */ if (fp < low + 12 || fp > high - 4) return -EINVAL; @@ -42,6 +65,7 @@ int notrace unwind_frame(struct stackframe *frame) frame->fp = *(unsigned long *)(fp - 12); frame->sp = *(unsigned long *)(fp - 8); frame->pc = *(unsigned long *)(fp - 4); +#endif return 0; } -- 2.27.0.212.ge8ba1cc988-goog
