On Tue Dec 19, 2023 at 10:22 PM AEST, Thomas Huth wrote: > 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 <npiggin@xxxxxxxxx> > > --- > > 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? No I think it's correct. INT_FRAME_SIZE has STACK_FRAME_OVERHEAD and struct pt_regs. The STACK_FRAME_OVERHEAD in GPR offsets is just to skip that and get to pt_regs.gpr[]. Thanks, Nick
