On 16/12/2023 14.42, Nicholas Piggin wrote:
The backtrace handler terminates when it sees a NULL caller address,
but the powerpc stack setup does not keep such a NULL caller frame
at the start of the stack.
This happens to work on pseries because the memory at 0 is mapped and
it contains 0 at the location of the return address pointer if it
were a stack frame. But this is fragile, and does not work with powernv
where address 0 contains firmware instructions.
Use the existing dummy frame on stack as the NULL caller, and create a
new frame on stack for the entry code.
Signed-off-by: Nicholas Piggin <npig...@gmail.com>
---
powerpc/cstart64.S | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)
diff --git a/powerpc/cstart64.S b/powerpc/cstart64.S
index e18ae9a2..14ab0c6c 100644
--- a/powerpc/cstart64.S
+++ b/powerpc/cstart64.S
@@ -46,8 +46,16 @@ start:
add r1, r1, r31
add r2, r2, r31
+ /* Zero backpointers in initial stack frame so backtrace() stops */
+ li r0,0
+ std r0,0(r1)
+ std r0,16(r1)
+
+ /* Create entry frame */
+ stdu r1,-INT_FRAME_SIZE(r1)
Shouldn't that rather be STACK_FRAME_OVERHEAD instead of INT_FRAME_SIZE...
/* save DTB pointer */
- std r3, 56(r1)
+ SAVE_GPR(3,r1)
... since SAVE_GPR uses STACK_FRAME_OVERHEAD (via GPR0), too?
Thomas
