Re: [PATCH 1/3] net: bpf jit: ppc: optimize choose_load_func error path

Jan Seiffert
2013-10-08T22:50:37Z

Vladimir Murzin schrieb:
> Macro CHOOSE_LOAD_FUNC returns handler for "any offset" if checks for K
> were not passed. At the same time handlers for "any offset" cases make
> the same checks against r_addr at run-time, that will always lead to
> bpf_error.
>

Hmmm, if i only would remember why i wrote it that way....
I memory serves me right the idea was to always have a solid fall back, no
matter what, to the generic load function which works more like the load_pointer
from filter.c.
This way the COOSE-macro may could have been used at more places, but that
never played out.

And since all i wanted was to get the negative indirect load fixed,
optimizing the constant error case was not on my plate.
That you can get your negative K filter JITed in the first place, even
if the constant error case was slower than necessary, was good enough ;)

The ARM JIT is broken till this date...

You can have my
I'm-OK-with-this: Jan Seiffert <kaffeemonster@googlemail.com>

for all three patches, -ENOTIME for a full review ATM.

> Run-time checks are still necessary for indirect load operations, but
> error path for absolute and mesh loads are worth to optimize during bpf
> compile time.
>
> Signed-off-by: Vladimir Murzin <murzin.v@gmail.com>
>
> Cc: Jan Seiffert <kaffeemonster@googlemail.com>
> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Cc: Paul Mackerras <paulus@samba.org>
> Cc: Daniel Borkmann <dborkman@redhat.com>
> Cc: Matt Evans <matt@ozlabs.org>
>
> ---
> arch/powerpc/net/bpf_jit_comp.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
> index bf56e33..754320a 100644
> --- a/arch/powerpc/net/bpf_jit_comp.c
> +++ b/arch/powerpc/net/bpf_jit_comp.c
> @@ -132,7 +132,7 @@ static void bpf_jit_build_epilogue(u32 *image, struct codegen_context *ctx)
> }
>
> #define CHOOSE_LOAD_FUNC(K, func) \
> - ((int)K < 0 ? ((int)K >= SKF_LL_OFF ? func##_negative_offset : func) : func##_positive_offset)
> + ((int)K < 0 ? ((int)K >= SKF_LL_OFF ? func##_negative_offset : NULL) : func##_positive_offset)
>
> /* Assemble the body code between the prologue & epilogue. */
> static int bpf_jit_build_body(struct sk_filter *fp, u32 *image,
> @@ -427,6 +427,11 @@ static int bpf_jit_build_body(struct sk_filter *fp, u32 *image,
> case BPF_S_LD_B_ABS:
> func = CHOOSE_LOAD_FUNC(K, sk_load_byte);
> common_load:
> + if (!func) {
> + PPC_LI(r_ret, 0);
> + PPC_JMP(exit_addr);
> + break;
> + }
> /* Load from [K]. */
> ctx->seen |= SEEN_DATAREF;
> PPC_LI64(r_scratch1, func);
>

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