[PATCH] arm: Add unwinding annotations for 64bit division functions

On Mon, September 19, 2011 4:22 pm, Nicolas Pitre wrote:

On Mon, 19 Sep 2011, Laura Abbott wrote:

quoted

The 64bit division functions never had unwinding annotations
added. This prevents a backtrace from being printed within
the function and if a division by 0 occurs. Add the annotations.

Signed-off-by: Laura Abbott <redacted>
---
 arch/arm/lib/div64.S |    8 ++++++++
 1 files changed, 8 insertions(+), 0 deletions(-)

diff --git a/arch/arm/lib/div64.S b/arch/arm/lib/div64.S
index faa7748..e55c484 100644
--- a/arch/arm/lib/div64.S
+++ b/arch/arm/lib/div64.S

@@ -13,6 +13,7 @@
  */

 #include <linux/linkage.h>
+#include <asm/unwind.h>

 #ifdef __ARMEB__
 #define xh r0

@@ -44,6 +45,7 @@
  */

 ENTRY(__do_div64)
+UNWIND(.fnstart)

 	@ Test for easy paths first.
 	subs	ip, r4, #1

@@ -189,7 +191,12 @@ ENTRY(__do_div64)
 	moveq	yh, xh
 	moveq	xh, #0
 	moveq	pc, lr
+UNWIND(.fnend)

+UNWIND(.fnstart)
+UNWIND(.pad #4)
+UNWIND(.save {lr})
+Ldiv0_64:

Why this phony fnend+fnstart here?

If a division by 0 occurs, we need to be able to access the saved LR on
the stack which is setup right before calling the __div0 function. This
can't go at the top of __do_div64 because if we try to do a backtrace from
within __do_div64 the annotation won't be correct as the LR was never
saved on the stack. (yes, __do_div64 is all register math but it's still
possible to take a prefetch abort in the middle of that function. Taking a
prefetch abort in the middle of __do_div64 is what found this issue in the
first place.) This setup handles both cases correctly.

Nicolas

Laura

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