From: Stanislav Fomichev <sdf@fomichev.me>
To: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Shuah Khan <shuah@kernel.org>,
Alexei Starovoitov <ast@kernel.org>,
Stanislav Fomichev <sdf@google.com>,
Daniel Borkmann <daniel@iogearbox.net>,
Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
Yonghong Song <yhs@fb.com>,
linux-kselftest@vger.kernel.org, netdev@vger.kernel.org,
bpf@vger.kernel.org
Subject: Re: [PATCHv2 bpf-next 1/3] bpf, tests: tweak endianness selection
Date: Wed, 20 Mar 2019 10:13:32 -0700 [thread overview]
Message-ID: <20190320171332.GJ7431@mini-arch.hsd1.ca.comcast.net> (raw)
In-Reply-To: <20190320125335.19621-1-sergey.senozhatsky@gmail.com>
On 03/20, 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:
>
> error: implicit declaration of function '__builtin_bswap16'
>
> We can use __builtin_bswap16() only if compiler has this built-in,
> that is, only if __HAVE_BUILTIN_BSWAP16__ is defined. Standard UAPI
> __swab16()/__swab32() take care of that, and, additionally, handle
> __builtin_constant_p() cases as well:
>
> #ifdef __HAVE_BUILTIN_BSWAP16__
> #define __swab16(x) (__u16)__builtin_bswap16((__u16)(x))
> #else
> #define __swab16(x) \
> (__builtin_constant_p((__u16)(x)) ? \
> ___constant_swab16(x) : \
> __fswab16(x))
> #endif
>
> So we can tweak selftests/bpf/bpf_endian.h and use UAPI
> __swab16()/__swab32().
>
> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
> ---
>
> v2: fixed build error, reshuffled patches (Stanislav Fomichev)
Tested them locally with the compiler I saw the initial issues with - all
fine, I don't see any errors with the older gcc.
One last question I have is: what happens in the llvm+bpf case? Have
you tested that? I think LLVM has all the builtins required, but since
we are relying on the swab.h now (and it relies on
__HAVE_BUILTIN_BSWAP16__), I wonder whether this detection works
correctly on the llvm when targeting bpf. (sidenote: bpf_endian.h can be
used from both userspace and bpf programs).
>
> tools/testing/selftests/bpf/bpf_endian.h | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/bpf_endian.h b/tools/testing/selftests/bpf/bpf_endian.h
> index b25595ea4a78..1ed268b2002b 100644
> --- a/tools/testing/selftests/bpf/bpf_endian.h
> +++ b/tools/testing/selftests/bpf/bpf_endian.h
> @@ -20,12 +20,12 @@
> * use different targets.
> */
> #if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
> -# define __bpf_ntohs(x) __builtin_bswap16(x)
> -# define __bpf_htons(x) __builtin_bswap16(x)
> +# define __bpf_ntohs(x) __swab16(x)
> +# define __bpf_htons(x) __swab16(x)
> # define __bpf_constant_ntohs(x) ___constant_swab16(x)
> # define __bpf_constant_htons(x) ___constant_swab16(x)
> -# define __bpf_ntohl(x) __builtin_bswap32(x)
> -# define __bpf_htonl(x) __builtin_bswap32(x)
> +# define __bpf_ntohl(x) __swab32(x)
> +# define __bpf_htonl(x) __swab32(x)
> # define __bpf_constant_ntohl(x) ___constant_swab32(x)
> # define __bpf_constant_htonl(x) ___constant_swab32(x)
> #elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
> --
> 2.21.0
>
next prev parent reply other threads:[~2019-03-20 17:13 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-20 12:53 [PATCHv2 bpf-next 1/3] bpf, tests: tweak endianness selection Sergey Senozhatsky
2019-03-20 12:53 ` [PATCHv2 bpf-next 2/3] bpf, tests: drop unused __bpf_constant_foo defines Sergey Senozhatsky
2019-03-20 12:56 ` Sergey Senozhatsky
2019-03-20 12:53 ` [PATCHv2 bpf-next 3/3] bpf, tests: don't use __bpf_constant_htons() Sergey Senozhatsky
2019-03-20 12:55 ` Sergey Senozhatsky
2019-03-20 17:13 ` Stanislav Fomichev [this message]
2019-03-20 22:20 ` [PATCHv2 bpf-next 1/3] bpf, tests: tweak endianness selection Yonghong Song
2019-03-20 22:27 ` Stanislav Fomichev
2019-03-20 22:45 ` Yonghong Song
2019-03-20 23:08 ` Daniel Borkmann
2019-03-21 0:03 ` Stanislav Fomichev
2019-03-21 0:23 ` Yonghong Song
2019-03-21 0:34 ` Sergey Senozhatsky
2019-03-21 0:22 ` Sergey Senozhatsky
2019-03-21 3:24 ` Alexei Starovoitov
2019-03-21 5:08 ` Sergey Senozhatsky
2019-03-21 15:49 ` Stanislav Fomichev
2019-03-22 2:46 ` Sergey Senozhatsky
2019-03-22 3:12 ` Alexei Starovoitov
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190320171332.GJ7431@mini-arch.hsd1.ca.comcast.net \
--to=sdf@fomichev.me \
--cc=ast@kernel.org \
--cc=bpf@vger.kernel.org \
--cc=daniel@iogearbox.net \
--cc=kafai@fb.com \
--cc=linux-kselftest@vger.kernel.org \
--cc=netdev@vger.kernel.org \
--cc=sdf@google.com \
--cc=sergey.senozhatsky@gmail.com \
--cc=shuah@kernel.org \
--cc=songliubraving@fb.com \
--cc=yhs@fb.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).