Messages in this thread | | | Date | Tue, 10 Jul 2018 18:49:05 +0100 | From | Okash Khawaja <> | Subject | Re: [PATCH bpf 1/1] bpf: btf: Fix bitfield extraction for big endian |
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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
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