On 2/27/23 10:56, Michael Ellerman wrote: > David Binderman <dcb314@xxxxxxxxxxx> writes: >> Hello there, >> >> I ran the static analyser cppcheck over the linux-6.2 source code and got this: >> >> linux-6.2/tools/testing/selftests/powerpc/pmu/sampling_tests/mmcra_thresh_marked_sample_test.c:68:10: style: Same expression '0x3' found multiple times in chain of '&' operators. [duplicateExpression] Hi, Thanks David for reporting it. > > Thanks. > >> Source code is >> >> FAIL_IF(EV_CODE_EXTRACT(event.attr.config, sample & 0x3) != >> get_mmcra_sample_mode(get_reg_value(intr_regs, "MMCRA"), 4)); >> >> but >> >> #define EV_CODE_EXTRACT(x, y) \ >> ((x >> ev_shift_##y) & ev_mask_##y) >> >> >> Given the token pasting, I very much doubt an expression like "sample & 0x3" >> will work correctly. Same thing on the line above >> >> FAIL_IF(EV_CODE_EXTRACT(event.attr.config, sample >> 2) != >> get_mmcra_rand_samp_elig(get_reg_value(intr_regs, "MMCRA"), 4)); >> >> "sample >> 2" doesn't look like a valid token to me. > > It expands to: > > if ((((event.attr.config >> ev_shift_sample >> 2) & ev_mask_sample >> 2) != get_mmcra_rand_samp_elig(get_reg_value(intr_regs, "MMCRA"), 4))) > > Which AFAICS is valid, and does compile. > > Whether it's what the author actually intended is less clear. > > And the other example with & 0x3 seems obviously wrong, it expands to: > > if ((((event.attr.config >> ev_shift_sample & 0x3) & ev_mask_sample & 0x3) != get_mmcra_sample_mode(get_reg_value(intr_regs, "MMCRA"), 4))) > > The shift is 24, so bitwise anding it with 0x3 gets 0 which doesn't seem > likely to be what was intended. > Hi Michael, Thanks for checking it. The intention is to check 3 bits of rand_samp_elig field and 2 bits of rand_samp_mode field from the sampling bits. Basically we first want to extract that sample field using EV_CODE_EXTRACT macro and then fetch required value of rand_samp_elig and rand_samp_mode, to compare it with MMCRA bits. Right approach to do that would be: FAIL_IF((EV_CODE_EXTRACT(event.attr.config, sample) >> 2) != get_mmcra_rand_samp_elig(get_reg_value(intr_regs, "MMCRA"), 4)); FAIL_IF((EV_CODE_EXTRACT(event.attr.config, sample) & 0x3) != get_mmcra_rand_samp_elig(get_reg_value(intr_regs, "MMCRA"), 4)); I will send a fix patch for same. Thanks, Kajol Jain > cheers
