From: Okash Khawaja <osk@fb•com>
To: Daniel Borkmann <daniel@iogearbox•net>
Cc: Martin KaFai Lau <kafai@fb•com>,
Alexei Starovoitov <ast@kernel•org>, Yonghong Song <yhs@fb•com>,
Jakub Kicinski <jakub.kicinski@netronome•com>,
"David S. Miller" <davem@davemloft•net>, <netdev@vger•kernel.org>,
<kernel-team@fb•com>, <linux-kernel@vger•kernel.org>
Subject: Re: [PATCH bpf 1/1] bpf: btf: Fix bitfield extraction for big endian
Date: Tue, 10 Jul 2018 18:49:05 +0100 [thread overview]
Message-ID: <20180710174904.GA3247@w1t1fb> (raw)
In-Reply-To: <58136182-0eb1-78c9-ceb9-402418c7d10c@iogearbox.net>
On Tue, Jul 10, 2018 at 10:21:02AM +0200, Daniel Borkmann wrote:
> On 07/09/2018 08:32 PM, Martin KaFai Lau wrote:
> > On Sun, Jul 08, 2018 at 05:22:03PM -0700, Okash Khawaja wrote:
> >> When extracting bitfield from a number, btf_int_bits_seq_show() builds
> >> a mask and accesses least significant byte of the number in a way
> >> specific to little-endian. This patch fixes that by checking endianness
> >> of the machine and then shifting left and right the unneeded bits.
> >>
> >> Thanks to Martin Lau for the help in navigating potential pitfalls when
> >> dealing with endianess and for the final solution.
> >>
> >> Fixes: b00b8daec828 ("bpf: btf: Add pretty print capability for data with BTF type info")
> >> Signed-off-by: Okash Khawaja <osk@fb•com>
> >>
> >> ---
> >> kernel/bpf/btf.c | 32 +++++++++++++++-----------------
> >> 1 file changed, 15 insertions(+), 17 deletions(-)
> >>
> >> --- a/kernel/bpf/btf.c
> >> +++ b/kernel/bpf/btf.c
> >> @@ -162,6 +162,8 @@
> >> #define BITS_ROUNDDOWN_BYTES(bits) ((bits) >> 3)
> >> #define BITS_ROUNDUP_BYTES(bits) \
> >> (BITS_ROUNDDOWN_BYTES(bits) + !!BITS_PER_BYTE_MASKED(bits))
> >> +const int one = 1;
> >> +#define is_big_endian() ((*(char *)&one) == 0)
>
> Also here, in the kernel archs provide proper definitions.
Is this the __BIG_ENDIAN #define or are there better ways to check that?
Thanks,
Okash
next prev parent reply other threads:[~2018-07-10 17:49 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-09 0:22 [PATCH bpf 0/1] bpf: btf: Fix endianness of bitfields Okash Khawaja
2018-07-09 0:22 ` [PATCH bpf 1/1] bpf: btf: Fix bitfield extraction for big endian Okash Khawaja
2018-07-09 17:32 ` Martin KaFai Lau
2018-07-09 18:32 ` Martin KaFai Lau
2018-07-10 8:21 ` Daniel Borkmann
2018-07-10 17:49 ` Okash Khawaja [this message]
2018-07-10 20:02 ` Daniel Borkmann
2018-07-10 16:35 ` David Laight
2018-07-10 17:18 ` Martin KaFai Lau
2018-07-10 18:13 ` Daniel Borkmann
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