On Fri Mar 1, 2024 at 7:53 PM AEST, Thomas Huth wrote:
> On 26/02/2024 11.11, Nicholas Piggin wrote:
> > Add support for backtracing across interrupt stacks, and
> > add interrupt frame backtrace for unhandled interrupts.
> >
> > Signed-off-by: Nicholas Piggin <npiggin@xxxxxxxxx>
> > ---
> > lib/powerpc/processor.c | 4 ++-
> > lib/ppc64/asm/stack.h | 3 +++
> > lib/ppc64/stack.c | 55 +++++++++++++++++++++++++++++++++++++++++
> > powerpc/Makefile.ppc64 | 1 +
> > powerpc/cstart64.S | 7 ++++--
> > 5 files changed, 67 insertions(+), 3 deletions(-)
> > create mode 100644 lib/ppc64/stack.c
> >
> > diff --git a/lib/powerpc/processor.c b/lib/powerpc/processor.c
> > index ad0d95666..114584024 100644
> > --- a/lib/powerpc/processor.c
> > +++ b/lib/powerpc/processor.c
> > @@ -51,7 +51,9 @@ void do_handle_exception(struct pt_regs *regs)
> > return;
> > }
> >
> > - printf("unhandled cpu exception %#lx at NIA:0x%016lx MSR:0x%016lx\n", regs->trap, regs->nip, regs->msr);
> > + printf("Unhandled cpu exception %#lx at NIA:0x%016lx MSR:0x%016lx\n",
> > + regs->trap, regs->nip, regs->msr);
> > + dump_frame_stack((void *)regs->nip, (void *)regs->gpr[1]);
> > abort();
> > }
> >
> > diff --git a/lib/ppc64/asm/stack.h b/lib/ppc64/asm/stack.h
> > index 9734bbb8f..94fd1021c 100644
> > --- a/lib/ppc64/asm/stack.h
> > +++ b/lib/ppc64/asm/stack.h
> > @@ -5,4 +5,7 @@
> > #error Do not directly include <asm/stack.h>. Just use <stack.h>.
> > #endif
> >
> > +#define HAVE_ARCH_BACKTRACE
> > +#define HAVE_ARCH_BACKTRACE_FRAME
> > +
> > #endif
> > diff --git a/lib/ppc64/stack.c b/lib/ppc64/stack.c
> > new file mode 100644
> > index 000000000..fcb7fa860
> > --- /dev/null
> > +++ b/lib/ppc64/stack.c
> > @@ -0,0 +1,55 @@
> > +#include <libcflat.h>
> > +#include <asm/ptrace.h>
> > +#include <stack.h>
> > +
> > +extern char exception_stack_marker[];
> > +
> > +int backtrace_frame(const void *frame, const void **return_addrs, int max_depth)
> > +{
> > + static int walking;
> > + int depth = 0;
> > + const unsigned long *bp = (unsigned long *)frame;
> > + void *return_addr;
> > +
> > + asm volatile("" ::: "lr"); /* Force it to save LR */
> > +
> > + if (walking) {
> > + printf("RECURSIVE STACK WALK!!!\n");
> > + return 0;
> > + }
> > + walking = 1;
> > +
> > + bp = (unsigned long *)bp[0];
> > + return_addr = (void *)bp[2];
> > +
> > + for (depth = 0; bp && depth < max_depth; depth++) {
> > + return_addrs[depth] = return_addr;
> > + if (return_addrs[depth] == 0)
> > + break;
> > + if (return_addrs[depth] == exception_stack_marker) {
> > + struct pt_regs *regs;
> > +
> > + regs = (void *)bp + STACK_FRAME_OVERHEAD;
> > + bp = (unsigned long *)bp[0];
> > + /* Represent interrupt frame with vector number */
> > + return_addr = (void *)regs->trap;
> > + if (depth + 1 < max_depth) {
> > + depth++;
> > + return_addrs[depth] = return_addr;
> > + return_addr = (void *)regs->nip;
> > + }
> > + } else {
> > + bp = (unsigned long *)bp[0];
> > + return_addr = (void *)bp[2];
> > + }
> > + }
> > +
> > + walking = 0;
> > + return depth;
> > +}
> > +
> > +int backtrace(const void **return_addrs, int max_depth)
> > +{
> > + return backtrace_frame(__builtin_frame_address(0), return_addrs,
> > + max_depth);
> > +}
> > diff --git a/powerpc/Makefile.ppc64 b/powerpc/Makefile.ppc64
> > index b0ed2b104..eb682c226 100644
> > --- a/powerpc/Makefile.ppc64
> > +++ b/powerpc/Makefile.ppc64
> > @@ -17,6 +17,7 @@ cstart.o = $(TEST_DIR)/cstart64.o
> > reloc.o = $(TEST_DIR)/reloc64.o
> >
> > OBJDIRS += lib/ppc64
> > +cflatobjs += lib/ppc64/stack.o
> >
> > # ppc64 specific tests
> > tests = $(TEST_DIR)/spapr_vpa.elf
> > diff --git a/powerpc/cstart64.S b/powerpc/cstart64.S
> > index 14ab0c6c8..278af84a6 100644
> > --- a/powerpc/cstart64.S
> > +++ b/powerpc/cstart64.S
> > @@ -188,6 +188,7 @@ call_handler:
> > .endr
> > mfsprg1 r0
> > std r0,GPR1(r1)
> > + std r0,0(r1)
> >
> > /* lr, xer, ccr */
> >
> > @@ -206,12 +207,12 @@ call_handler:
> > subi r31, r31, 0b - start_text
> > ld r2, (p_toc_text - start_text)(r31)
> >
> > - /* FIXME: build stack frame */
> > -
> > /* call generic handler */
> >
> > addi r3,r1,STACK_FRAME_OVERHEAD
> > bl do_handle_exception
> > + .global exception_stack_marker
> > +exception_stack_marker:
> >
> > /* restore context */
> >
> > @@ -321,6 +322,7 @@ handler_trampoline:
> > /* nip and msr */
> > mfsrr0 r0
> > std r0, _NIP(r1)
> > + std r0, INT_FRAME_SIZE+16(r1)
>
> So if I got that right, INT_FRAME_SIZE+16 points to the stack frame of the
> function that was running before the interrupt handler? Is it such a good
> idea to change that here?
No, we switch to exception stack and don't support recursing interrupts
on stack at the moment, so this goes into the initial frame.
> Please add a comment here explaining this line.
> Thanks!
Yes, good idea.
Thanks,
Nick
>
>
> > mfsrr1 r0
> > std r0, _MSR(r1)
> > @@ -337,6 +339,7 @@ handler_htrampoline:
> > /* nip and msr */
> > mfspr r0, SPR_HSRR0
> > std r0, _NIP(r1)
> > + std r0, INT_FRAME_SIZE+16(r1)
>
> dito.
>
> > mfspr r0, SPR_HSRR1
> > std r0, _MSR(r1)
>
> Thomas
