Re: [PATCH v4 2/2] selftests/bpf: Add tests for sdiv32/smod32 with INT_MIN dividend

[Jiayuan Chen <jiayuan.chen@linux.dev>]

On 3/10/26 5:59 AM, Jenny Guanni Qu wrote:
> Add tests to verify that signed 32-bit division and modulo operations
> produce correct results when the dividend is INT_MIN (0x80000000).
>
> The bug fixed in the previous commit only affects the BPF interpreter
> path. When JIT is enabled (the default on most architectures), the
> native CPU division instruction produces the correct result and these
> tests pass regardless. With bpf_jit_enable=0, the interpreter is used
> and without the previous fix, INT_MIN / 2 incorrectly returns
> 0x40000000 instead of 0xC0000000 due to abs(S32_MIN) undefined
> behavior, causing these tests to fail.
>
> Test cases:
>    - SDIV32 INT_MIN / 2 = -1073741824 (imm and reg divisor)
>    - SMOD32 INT_MIN % 2 = 0 (positive and negative divisor)
>
> Signed-off-by: Jenny Guanni Qu <qguanni@gmail.com>
> ---
>   .../selftests/bpf/progs/verifier_sdiv.c       | 58 +++++++++++++++++++
>   1 file changed, 58 insertions(+)
>
> diff --git a/tools/testing/selftests/bpf/progs/verifier_sdiv.c b/tools/testing/selftests/bpf/progs/verifier_sdiv.c
> index 148d2299e5b4..fd59d57e8e37 100644
> --- a/tools/testing/selftests/bpf/progs/verifier_sdiv.c
> +++ b/tools/testing/selftests/bpf/progs/verifier_sdiv.c
> @@ -1209,6 +1209,64 @@ __naked void smod32_ri_divisor_neg_1(void)
>   	: __clobber_all);
>   }
>   
> +SEC("socket")
> +__description("SDIV32, INT_MIN divided by 2, imm")
> +__success __success_unpriv __retval(-1073741824)
> +__naked void sdiv32_int_min_div_2_imm(void)
> +{
> +	asm volatile ("					\
> +	w0 = %[int_min];				\
> +	w0 s/= 2;					\
> +	exit;						\
> +"	:
> +	: __imm_const(int_min, INT_MIN)
> +	: __clobber_all);
> +}
> +
> +SEC("socket")
> +__description("SDIV32, INT_MIN divided by 2, reg")
> +__success __success_unpriv __retval(-1073741824)
> +__naked void sdiv32_int_min_div_2_reg(void)
> +{
> +	asm volatile ("					\
> +	w0 = %[int_min];				\
> +	w1 = 2;						\
> +	w0 s/= w1;					\
> +	exit;						\
> +"	:
> +	: __imm_const(int_min, INT_MIN)
> +	: __clobber_all);
> +}
> +
> +SEC("socket")
> +__description("SMOD32, INT_MIN modulo 2, imm")
> +__success __success_unpriv __retval(0)
> +__naked void smod32_int_min_mod_2_imm(void)
> +{
> +	asm volatile ("					\
> +	w0 = %[int_min];				\
> +	w0 s%%= 2;					\
> +	exit;						\
> +"	:
> +	: __imm_const(int_min, INT_MIN)
> +	: __clobber_all);
> +}
> +
> +SEC("socket")
> +__description("SMOD32, INT_MIN modulo -2, imm")
> +__success __success_unpriv __retval(0)
> +__naked void smod32_int_min_mod_neg2_imm(void)
> +{
> +	asm volatile ("					\
> +	w0 = %[int_min];				\
> +	w0 s%%= -2;					\
> +	exit;						\
> +"	:
> +	: __imm_const(int_min, INT_MIN)
> +	: __clobber_all);
> +}
> +
> +
>   #else
>   


Minor nits: extra blank line before #else, and smod32 tests only cover 
the imm
form — a reg variant (w0 s%%= w1) would make coverage symmetric with sdiv32.

Neither worth a respin.

Reviewed-by: Jiayuan Chen <jiayuan.chen@linux.dev>

>   SEC("socket")