powerpc/lib: fix unsafe register handling in wait_ticks
PATCH 1/1 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.
--- arch/powerpc/lib/ticks.S | 17 +++++++++++------ 1 files changed, 11 insertions(+), 6 deletions(-)
arch/powerpc/lib/ticks.S +11 -6
@@ -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
Signature · 1 line
1.7.1
PATCH 1/1 powerpc/lib: fix unsafe register handling in wait_ticks
Quoted 10 lines · Mats K?rrman
If watchdog is enabled, the arch/powerpc/lib/ticks.S::wait_ticks() function calls the function specified by the
WATCHDOG_RESETmacro.
Thewait_ticksfunction 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.
Quoted 6 lines
The patch has been tested on a custom MPC5125 based machine using the 512x powerpc architecture.
Signed-off-by Mats Karrman <[email protected]>Cc Wolfgang Denk <[email protected]>Acked-by Joakim Tjernlund <[email protected]>
Thanks for this fix. I just reproduced this problem on another MPC5200 based board (a4m2k) while implementing watchdog support. And this patch fixes the problem (hangup in wait_ticks).
So:
Thanks,
Stefan
PATCH 1/1 powerpc/lib: fix unsafe register handling in wait_ticks
Quoted 3 lines · Mats K?rrman
Quoted 1 line
If watchdog is enabled, the arch/powerpc/lib/ticks.S::wait_ticks()
function
Quoted 3 lines
Quoted 3 lines
calls the function specified by the
WATCHDOG_RESETmacro. Thewait_ticksfunction depends on the registers r0, r6 and r7 being preserved however that is not guaranteed, e.g. if the reset function
is a
Quoted 3 lines
Quoted 3 lines
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
Quoted 1 line
Quoted 1 line
what would have been generated by a C compiler) and saves all
necessary
Quoted 3 lines
Quoted 3 lines
registers on the stack.
The patch has been tested on a custom MPC5125 based machine using the
512x
Quoted 6 lines
Quoted 5 lines
powerpc architecture.
Signed-off-by Mats Karrman <[email protected]>Cc Wolfgang Denk <[email protected]>Acked-by Joakim Tjernlund <[email protected]>
Quoted 7 lines
Thanks for this fix. I just reproduced this problem on another MPC5200 based board (a4m2k) while implementing watchdog support. And this patch fixes the problem (hangup in
wait_ticks).So:
Tested-by Stefan Roese <[email protected]>
If someone wants to play with a C only impl. I THINK it this is a good starting point:
#define WATCHDOG_RESET
/*static inline */unsigned long long get_ticks(void)
{
union xx {
unsigned long long r3_r4;
struct yx {
unsigned long r3;
unsigned long r4;
} xy;
} res;
register unsigned long tmp;
do {
asm ("mftbu %0\n\t"
"mftb %1\n\t"
"mftbu %2"
: "=r"(res.xy.r3), "=r"(res.xy.r4), "=r"(tmp));
} while (res.xy.r3 != tmp);
return res.r3_r4;
}wait_ticks(unsigned long wt)
{
unsigned long long ticks_end;
ticks_end = get_ticks() + wt;
WATCHDOG_RESET;
do {
} while((signed long long)ticks_end - (signed long long)get_ticks() >= 0);
}
Quoted 10 lines · On Sun, Jan 27, 2013 at 07:03:44AM -0000…
If watchdog is enabled, the arch/powerpc/lib/ticks.S::wait_ticks() function calls the function specified by the
WATCHDOG_RESETmacro.
Thewait_ticksfunction 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.
Quoted 7 lines
The patch has been tested on a custom MPC5125 based machine using the 512x powerpc architecture.
Signed-off-by Mats Karrman <[email protected]>Cc Wolfgang Denk <[email protected]>Acked-by Joakim Tjernlund <[email protected]>Tested-by Stefan Roese <[email protected]>
This does not cleanly apply to u-boot/master, can you please resend based on top of tree? Thanks!
Signature · 8 lines
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