linux-kernel - Re: [REGRESSION][PATCH V4 3/3] bpf jit: Let the powerpc jit handle negative offsets

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Date:	Mon, 30 Apr 2012 13:40:46 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	David Miller <davem@...emloft.net>
Cc:	kaffeemonster@...glemail.com, eric.dumazet@...il.com,
	matt@...abs.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [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 ?

Cheers,
Ben.


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