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

[Yonghong Song <yonghong.song@linux.dev>]

On 3/9/26 7:05 PM, Jiayuan Chen wrote:
>
> 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.

Right, the committer should be able to remove the extra line.

Acked-by: Yonghong Song <yonghong.song@linux.dev>

>
> Neither worth a respin.
>
> Reviewed-by: Jiayuan Chen <jiayuan.chen@linux.dev>
>
>>   SEC("socket")