Re: [PATCH bpf v5 2/2] selftests/bpf: Cover negative buffer pointer offsets

[Eduard Zingerman]

On Wed, 2026-07-15 at 13:26 +0800, sun jian wrote:

[...]

> > Anyway, still recommend adding a regression test that test access to one
> > byte before the start of writable context.
> > 
> 
> The new tracepoint_writable_reject_negative_const_offset verifier case
> already covers an access before the start of the writable context:
> 
>     r6 = *(u64 *)(r1 + 0);
>     r6 += -8;
>     r0 = *(u64 *)(r6 + 0);
> 
> Its effective access range is [-8, 0), so it is rejected at load time.
> This is the direct regression test for the negative-start case.

The existing test seem to be sufficient, why would it matter is at
offset -8 or -1 given that the read is appropriately sized?

The added test in tools/testing/selftests/bpf/progs/verifier_raw_tp_writable.c
is redundant given the changes in raw_tp_writable_reject_bad_access.c
but I was going to apply anyway.