RE: [PATCH v3 2/6] test/bpf: add JSET test with small immediate

[Marat Khalili <marat.khalili@huawei.com>]

This instruction has an interesting behavior for negative values of immediate,
to be thorough I would test them as well. Fixed x86 should pass but who knows.

I would also welcome a test reproducing the problem with shifts.

For the narrow scope of this test,

Acked-by: Marat Khalili <marat.khalili@huawei.com>

> -----Original Message-----
> From: Stephen Hemminger <stephen@networkplumber.org>
> Sent: Sunday 21 June 2026 17:24
> To: dev@dpdk.org
> Cc: Stephen Hemminger <stephen@networkplumber.org>; Konstantin Ananyev <konstantin.ananyev@huawei.com>;
> Marat Khalili <marat.khalili@huawei.com>
> Subject: [PATCH v3 2/6] test/bpf: add JSET test with small immediate
> 
> The existing jump test only used a 32-bit JSET mask,
> so the broken imm8 encoding of TEST in the x86 JIT was never exercised.
> Add a case with a byte-sized mask;
> run_test() runs it through the interpreter and the JIT.
> 
> Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> ---
>  app/test/test_bpf.c | 82 +++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 82 insertions(+)
> 
> diff --git a/app/test/test_bpf.c b/app/test/test_bpf.c
> index dd24722450..e70dea736f 100644
> --- a/app/test/test_bpf.c
> +++ b/app/test/test_bpf.c
> @@ -3158,7 +3158,89 @@ static const struct ebpf_insn test_ld_mbuf3_prog[] = {
>  };
> 
>  /* all bpf test cases */
> +/*
> + * JSET with a byte-sized mask: exercises the imm8 path of the TEST
> + * encoding in the x86 JIT (a 32-bit mask takes a different path).
> + */
> +static const struct ebpf_insn test_jset1_prog[] = {
> +	{
> +		.code = (BPF_ALU | EBPF_MOV | BPF_K),
> +		.dst_reg = EBPF_REG_0,
> +		.imm = 0,
> +	},
> +	{
> +		.code = (BPF_LDX | BPF_MEM | BPF_B),
> +		.dst_reg = EBPF_REG_2,
> +		.src_reg = EBPF_REG_1,
> +		.off = offsetof(struct dummy_offset, u8),
> +	},
> +	/* bit 0 is set in the input: branch is taken */
> +	{
> +		.code = (BPF_JMP | BPF_JSET | BPF_K),
> +		.dst_reg = EBPF_REG_2,
> +		.imm = 0x1,
> +		.off = 1,
> +	},
> +	{
> +		.code = (BPF_JMP | BPF_JA),
> +		.off = 1,
> +	},
> +	{
> +		.code = (EBPF_ALU64 | BPF_OR | BPF_K),
> +		.dst_reg = EBPF_REG_0,
> +		.imm = 0x1,
> +	},
> +	/* bit 1 is clear in the input: branch is not taken */
> +	{
> +		.code = (BPF_JMP | BPF_JSET | BPF_K),
> +		.dst_reg = EBPF_REG_2,
> +		.imm = 0x2,
> +		.off = 1,
> +	},
> +	{
> +		.code = (BPF_JMP | BPF_JA),
> +		.off = 1,
> +	},
> +	{
> +		.code = (EBPF_ALU64 | BPF_OR | BPF_K),
> +		.dst_reg = EBPF_REG_0,
> +		.imm = 0x2,
> +	},
> +	{
> +		.code = (BPF_JMP | EBPF_EXIT),
> +	},
> +};
> +
> +static void
> +test_jset1_prepare(void *arg)
> +{
> +	struct dummy_offset *df = arg;
> +
> +	memset(df, 0, sizeof(*df));
> +	df->u8 = 0x1;	/* bit 0 set, bit 1 clear */
> +}
> +
> +static int
> +test_jset1_check(uint64_t rc, const void *arg)
> +{
> +	return cmp_res(__func__, 0x1, rc, arg, arg, 0);
> +}
> +
>  static const struct bpf_test tests[] = {
> +	{
> +		.name = "test_jset1",
> +		.arg_sz = sizeof(struct dummy_offset),
> +		.prm = {
> +			.ins = test_jset1_prog,
> +			.nb_ins = RTE_DIM(test_jset1_prog),
> +			.prog_arg = {
> +				.type = RTE_BPF_ARG_PTR,
> +				.size = sizeof(struct dummy_offset),
> +			},
> +		},
> +		.prepare = test_jset1_prepare,
> +		.check_result = test_jset1_check,
> +	},
>  	{
>  		.name = "test_store1",
>  		.arg_sz = sizeof(struct dummy_offset),
> --
> 2.53.0