Re: [kvm-unit-tests PATCH 04/32] powerpc: interrupt stack backtracing

["Nicholas Piggin" <npiggin@gmail.com>]

On Wed Feb 28, 2024 at 9:46 PM AEST, Andrew Jones wrote:
> On Mon, Feb 26, 2024 at 08:11:50PM +1000, Nicholas Piggin wrote:
> > Add support for backtracing across interrupt stacks, and
> > add interrupt frame backtrace for unhandled interrupts.
> > 
> > Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> > ---
> >  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);
> > +}
>
> I'm about to post a series which has a couple treewide tracing changes
> in them. Depending on which series goes first the other will need to
> accommodate.

Yeah that's fine.

Thanks,
Nick