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powerpc/lib: fix unsafe register handling in wait_ticks 

If watchdog is enabled, the arch/powerpc/lib/ticks.S::wait_ticks() function
calls the function specified by the WATCHDOG_RESET macro.
The wait_ticks function depends on the registers r0, r6 and r7 being
preserved however that is not guaranteed, e.g. if the reset function is a
C function this will probably overwrite r0 and cause an endless loop.

The following patch changes to using r14+r15 instead of r6+r7 (to resemble
what would have been generated by a C compiler) and saves all necessary
registers on the stack.

The patch has been tested on a custom MPC5125 based machine using the 512x
powerpc architecture.

Signed-off-by: Mats Karrman <mats.karrman@tritech.se>
Cc: Wolfgang Denk <wd@denx.de>
Acked-by: Joakim Tjernlund <joakim.tjernlund@transmode.se>
Tested-by: Stefan Roese <sr@denx.de>
This commit is contained in:
Mats Kärrman 2013-04-09 17:10:59 +02:00 committed by Tom Rini
parent 645b271a60
commit fac150e83f
1 changed files with 11 additions and 6 deletions
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17
arch/powerpc/lib/ticks.S
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@ -50,19 +50,24 @@ wait_ticks:
stwu r1, -16(r1)
mflr r0 /* save link register */
stw r0, 20(r1) /* Use r0 or GDB will be unhappy */
mr r7, r3 /* save tick count */
stw r14, 12(r1) /* save used registers */
stw r15, 8(r1)
mr r14, r3 /* save tick count */
bl get_ticks /* Get start time */
/* Calculate end time */
addc r7, r4, r7 /* Compute end time lower */
addze r6, r3 /* and end time upper */
addc r14, r4, r14 /* Compute end time lower */
addze r15, r3 /* and end time upper */
WATCHDOG_RESET /* Trigger watchdog, if needed */
1: bl get_ticks /* Get current time */
subfc r4, r4, r7 /* Subtract current time from end time */
subfe. r3, r3, r6
subfc r4, r4, r14 /* Subtract current time from end time */
subfe. r3, r3, r15
bge 1b /* Loop until time expired */
mtlr r0 /* restore link register */
lwz r15, 8(r1) /* restore saved registers */
lwz r14, 12(r1)
lwz r0, 20(r1)
addi r1,r1,16
mtlr r0
blr