From: Daniel Borkmann <daniel@iogearbox.net>
To: Okash Khawaja <osk@fb.com>
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 22:02:07 +0200 [thread overview]
Message-ID: <939115f0-3457-75f2-c1df-4cfc6a53ba52@iogearbox.net> (raw)
In-Reply-To: <20180710174904.GA3247@w1t1fb>
On 07/10/2018 07:49 PM, Okash Khawaja wrote:
> 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?
Given this deals with bitfields, should be __{BIG,LITTLE}_ENDIAN_BITFIELD.
next prev parent reply other threads:[~2018-07-10 20:02 UTC|newest]
Thread overview: 9+ 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
[not found] ` <20180710174904.GA3247@w1t1fb>
2018-07-10 20:02 ` Daniel Borkmann [this message]
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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