Re: [PATCH] aarch64: Fix an infinite loop on bt when the core dump has an SVE section but the target does not support it.

[Luis Machado <luis.machado@arm.com>]

Hi,

On 3/19/23 20:55, Dmytro Medvied via Gdb-patches wrote:
> When read_aarch64_ctx() returns AARCH64_SVE_MAGIC and the target does not support SVE gdb goes in an infinite loop because the section was not incremented by the size of the read context.
> To fix this behavior, the section needs to be incremented by the size of the read context after the check for target supporting of SVE has returned false.
> ---
>   gdb/aarch64-linux-tdep.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/gdb/aarch64-linux-tdep.c b/gdb/aarch64-linux-tdep.c
> index b183a3c9a38..439760fffe2 100644
> --- a/gdb/aarch64-linux-tdep.c
> +++ b/gdb/aarch64-linux-tdep.c
> @@ -337,7 +337,10 @@ aarch64_linux_sigframe_init (const struct tramp_frame *self,
>   	    uint16_t vq;
>   
>   	    if (!tdep->has_sve ())
> -	      break;
> +	      {
> +		section += size;
> +		break;
> +	      }
>   
>   	    if (target_read_memory (section + AARCH64_SVE_CONTEXT_VL_OFFSET,
>   				    buf, 2) != 0)

That's interesting. If the target doesn't support SVE, why is the SVE_MAGIC context being generated in the first place?

It should've been handled by the default case, where we increment the section by the size.

If gdb knows about SVE, it should be able to handle it, unless the target says the vector length is 0.

Could you please clarify what target you observed this on?