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SubjectRe: [REGRESSION][PATCH V4 3/3] bpf jit: Let the powerpc jit handle negative offsets
On Mon, 2012-04-30 at 12:43 +1000, Benjamin Herrenschmidt wrote:

> Ok, he hasn't so I'll dig a bit.
> No obvious wrongness (but I'm not very familiar with bpf), though I do
> have a comment: sk_negative_common() and bpf_slow_path_common() should
> be made one and single macro which takes the fallback function as an
> argument.
> I'll mess around & try to test using Jan test case & will come back
> with an updated patch.

Wow, hit that nasty along the way: The test program will not work
on big endian machines because of a nasty difference between
the kernel struct sock_fprog and libpcap struct bpf_program:

Kernel expects:

struct sock_fprog { /* Required for SO_ATTACH_FILTER. */
unsigned short len; /* Number of filter blocks */
struct sock_filter __user *filter;

libpcap provides:

struct bpf_program {
u_int bf_len;
struct bpf_insn *bf_insns;

Note the unsigned short vs. unsigned int there ? This totally
breaks it here.

Is it expected that one can pass a struct bpf_program directly
to the kernel or should it be "converted" by the library in which
case it's just a bug in Jan's test program ?


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