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

[Eduard Zingerman <eddyz87@gmail.com>]

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.

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