[Pdbg] [PATCH] stack: unwinder fix endian heuristic at top of stack

[Alistair Popple]

On Friday, 28 June 2019 2:20:38 PM AEST Nicholas Piggin wrote:
> When the stack is followed to the top and the next backpointer is
> zero, the endian guess for the frame does not work properly. This
> changes it to remember the previous endianness and use that.
> 
> Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
> ---
> This stack unwinder is becoming a proper Rube Goldberg machine, it
> can probably be rewritten sanely and more reliably, but here's one
> last little fix I've been carrying around for a while that helps
> things.

Yeah, I convinced myself the original implementation worked but if these fixes 
make it more useful we can merge it and worry about sanity later :-)

Acked-by: Alistair Popple <alistair at popple.id.au>

>  src/thread.c | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/src/thread.c b/src/thread.c
> index 8f34233..ede797a 100644
> --- a/src/thread.c
> +++ b/src/thread.c
> @@ -57,6 +57,7 @@ static int dump_stack(struct thread_regs *regs, struct
> pdbg_target *adu) uint64_t next_sp = regs->gprs[1];
>  	uint64_t pc;
>  	bool finished = false;
> +	bool prev_flip = false;
> 
>  	printf("STACK:           SP                NIA\n");
>  	if (!(next_sp && is_real_address(regs, next_sp))) {
> @@ -82,13 +83,17 @@ static int dump_stack(struct thread_regs *regs, struct
> pdbg_target *adu) if (!load8(adu, sp + 16, &pc))
>  			return 1;
> 
> -		tmp2 = flip_endian(tmp);
> -
>  		if (!tmp) {
>  			finished = true;
> -			goto no_flip;
> +			flip = prev_flip;
> +			if (flip)
> +				be = !be;
> +			next_sp = 0;
> +			goto do_pc;
>  		}
> 
> +		tmp2 = flip_endian(tmp);
> +
>  		/*
>  		 * Basic endian detection.
>  		 * Stack grows down, so as we unwind it we expect to see
> @@ -130,11 +135,14 @@ no_flip:
>  			next_sp = tmp;
>  		}
> 
> +do_pc:
>  		if (flip)
>  			pc = flip_endian(pc);
> 
>  		printf(" 0x%016" PRIx64 " 0x%016" PRIx64 " (%s)\n",
>  			sp, pc, be ? "big-endian" : "little-endian");
> +
> +		prev_flip = flip;
>  	}
>  	printf(" 0x%016" PRIx64 "\n", next_sp);