Re: [PATCH 2/2] selftests/bpf: tests to non_null ptr detection using register operand in JEQ/JNE

[Cupertino Miranda <cupertino.miranda@oracle.com>]

Hi Edward,

Thanks for the quick feedback.
Will prepare a v2, soon.

Cheers,
Cupertino

On 03-03-2026 6:12 PM, Eduard Zingerman wrote:
> On Mon, 2026-03-02 at 16:17 +0000, Cupertino Miranda wrote:
>> The 5 added tests are copies of the already existing tests in the same
>> file, but changed to use R3 instead of an immediate 0.
>>
>> Signed-off-by: Cupertino Miranda <cupertino.miranda@oracle.com>
>> Cc: David Faust  <david.faust@oracle.com>
>> Cc: Jose Marchesi  <jose.marchesi@oracle.com>
>> Cc: Elena Zannoni  <elena.zannoni@oracle.com>
>> ---
> 
> I think this is an overkill, these tests check nullness propagation
> over id chains etc. For the purpose of this change something like
> below should suffice:
> 
> +SEC("xdp")
> +__success __log_level(2)
> +/* to make sure the branch is not falsely predicted*/
> +__msg("r0 = *(u32 *)(r0 +0)")
> +__msg("from 7 to 9")
> +__naked void jeq_reg_reg_null_check(void)
> +{
> +        asm volatile ("                                 \
> +        *(u32*)(r10 - 8) = 0;                           \
> +        r1 = %[map_xskmap] ll;                          \
> +        r2 = r10;                                       \
> +        r2 += -8;                                       \
> +        call %[bpf_map_lookup_elem];                    \
> +        r1 = 0;                                         \
> +        if r0 == r1 goto 1f;                            \
> +        r0 = *(u32*)(r0 +0);                            \
> +1:      r0 = 0;                                         \
> +        exit;                                           \
> +"       :
> +        : __imm(bpf_map_lookup_elem),
> +          __imm_addr(map_xskmap)
> +        : __clobber_all);
> +}
> 
> And maybe a variant of this with `if r1 != r0` or maybe not.
> 
> [...]