ARM: 8992/1: Fix unwind_frame for clang-built kernels

commit b4d5ec9b39f8b31d98f65bc5577b5d15d93795d7 upstream.

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@mediatek.com>
Tested-by: Miles Chen <miles.chen@mediatek.com>
Cc: stable@vger.kernel.org
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Nathan Huckleberry <nhuck@google.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/arm/kernel/stacktrace.c b/arch/arm/kernel/stacktrace.c
index 65228bf4c6dfee221e4e3a38112c0d59ecda65f9..ba9b9a77bcd2c28ecae0198c5573c6f95337ed62 100644 (file)
--- a/arch/arm/kernel/stacktrace.c
+++ b/arch/arm/kernel/stacktrace.c
@@ -20,6 +20,19 @@
  * 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.
  */
@@ -32,6 +45,16 @@ 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;
@@ -40,6 +63,7 @@ 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;
 }