Subject: Re: [oss-drivers] netronome/nfp/bpf/jit.c cannot be build with -O3

From: Jiong Wang <[email-masked]>
Date: Tue, 07 May 2019 12:31:29 +0100

Oleksandr Natalenko writes:

> Hi.
>
> On 07.05.2019 00:01, Jiong Wang wrote:
>> I guess it's because constant prop. Could you try the following change 
>> to
>> __emit_shift?
>> 
>> drivers/net/ethernet/netronome/nfp/bpf/jit.c
>> __emit_shift:331
>> -       if (sc == SHF_SC_L_SHF)
>> +       if (sc == SHF_SC_L_SHF && shift)
>>                 shift = 32 - shift;
>> 
>> emit_shf_indir is passing "0" as shift to __emit_shift which will
>> eventually be turned into 32 and it was OK because we truncate to 
>> 5-bit,
>> but before truncation, it will overflow the shift mask.
>
> Yup, it silences the error for me.

Thanks for the testing.

I have also reproduced this issue after switching to gcc 8.3, and confirmed
the error is triggered from "value too large for the field" check inside
__BF_FIELD_CHECK due to immediate "32" is out of range for mask 0x1f.

Will send out a fix.

Regards,
Jiong