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

[Andrew Jones <andrew.jones@linux.dev>]

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.

Thanks,
drew