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

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Message-ID: <87ef5abiwe.fsf@netronome.com>
Date:   Tue, 07 May 2019 12:31:29 +0100
From:   Jiong Wang <jiong.wang@...ronome.com>
To:     Oleksandr Natalenko <oleksandr@...alenko.name>
Cc:     Jiong Wang <jiong.wang@...ronome.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        "David S. Miller" <davem@...emloft.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        netdev@...r.kernel.org, bpf@...r.kernel.org,
        oss-drivers@...ronome.com, linux-kernel@...r.kernel.org,
        xdp-newbies@...r.kernel.org, valdis@...edu
Subject: Re: [oss-drivers] netronome/nfp/bpf/jit.c cannot be build with -O3


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