netdev - Re: [PATCHv2 bpf-next 1/3] bpf, tests: tweak endianness selection

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Date:   Fri, 22 Mar 2019 11:46:52 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Stanislav Fomichev <sdf@...ichev.me>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Shuah Khan <shuah@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        linux-kselftest@...r.kernel.org, netdev@...r.kernel.org,
        bpf@...r.kernel.org
Subject: Re: [PATCHv2 bpf-next 1/3] bpf, tests: tweak endianness selection

On (03/21/19 08:49), Stanislav Fomichev wrote:
> On 03/21, Sergey Senozhatsky wrote:
> > On (03/20/19 20:24), Alexei Starovoitov wrote:
> > > On Wed, Mar 20, 2019 at 09:53:33PM +0900, Sergey Senozhatsky wrote:
> > > > Not all compilers have __builtin_bswap16() and __builtin_bswap32(),
> > > > thus not all compilers are able to compile the following code:
> > > > 
> > > >         (__builtin_constant_p(x) ? \
> > > >                 ___constant_swab16(x) : __builtin_bswap16(x))
> > > > 
> > > > That's the reason why bpf_ntohl() doesn't work on GCC < 4.8, for
> > > > instance:
> > > 
> > > nack to fixes to support such old compilers.
> > 
> > Fair enough.
> What is too old? Documentation/process/changes.rst says that minimum
> supported gcc is 4.6, do we lift that requirement for the tests?

Hmm, good point, Stanislav. I thought it was gcc 4.9 which introduced
asm goto and hence 4.9 is the minimum supported version. But it seems
that it was 4.5/4.6, so the min supported gcc version is 4.6. Which
means that those bpf defines won't work on some compilers.

Alexei, does your NACK still stand?

	-ss