linux-kernel - Re: [PATCH V3 2/3] ARM: net: bpf_jit: make code generation less dependent on struct sk

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Date:	Sat, 27 Apr 2013 00:01:10 +0200
From:	Daniel Borkmann <dborkman@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Arnd Bergmann <arnd@...db.de>,
	Nicolas Schichan <nschichan@...ebox.fr>,
	Will Drewry <wad@...omium.org>,
	Mircea Gherzan <mgherzan@...il.com>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Russell King <linux@....linux.org.uk>,
	"David S. Miller" <davem@...emloft.net>,
	Daniel Borkmann <daniel.borkmann@....ee.ethz.ch>,
	netdev@...r.kernel.org, Xi Wang <xi.wang@...il.com>
Subject: Re: [PATCH V3 2/3] ARM: net: bpf_jit: make code generation less dependent
 on struct sk_filter.

On 04/26/2013 10:09 PM, Andrew Morton wrote:
> On Fri, 26 Apr 2013 21:47:46 +0200 Daniel Borkmann <dborkman@...hat.com> wrote:
>> On 04/26/2013 09:26 PM, Andrew Morton wrote:
>>> On Fri, 26 Apr 2013 16:04:44 +0200 Arnd Bergmann <arnd@...db.de> wrote:
>>>> On Wednesday 24 April 2013 19:27:08 Nicolas Schichan wrote:
>>>>> @@ -858,7 +858,7 @@ b_epilogue:
>>>>>    }
>>>>>
>>>>>
>>>>> -void bpf_jit_compile(struct sk_filter *fp)
>>>>> +static void __bpf_jit_compile(struct jit_ctx *out_ctx)
>>>>>    {
>>>>>           struct jit_ctx ctx;
>>>>>           unsigned tmp_idx;
>>>>> @@ -867,11 +867,10 @@ void bpf_jit_compile(struct sk_filter *fp)
>>>>>           if (!bpf_jit_enable)
>>>>>                   return;
>>>>>
>>>>> -       memset(&ctx, 0, sizeof(ctx));
>>>>> -       ctx.skf         = fp;
>>>>> +       ctx = *out_ctx;
>>>>>           ctx.ret0_fp_idx = -1;
>>>>>
>>>>> -       ctx.offsets = kzalloc(4 * (ctx.skf->len + 1), GFP_KERNEL);
>>>>> +       ctx.offsets = kzalloc(4 * (ctx.prog_len + 1), GFP_KERNEL);
>>>>>           if (ctx.offsets == NULL)
>>>>>                   return;
>>>>>
>>>>> @@ -921,13 +920,26 @@ void bpf_jit_compile(struct sk_filter *fp)
>>>>>                   print_hex_dump(KERN_INFO, "BPF JIT code: ",
>>>>>                                  DUMP_PREFIX_ADDRESS, 16, 4, ctx.target,
>>>>>                                  alloc_size, false);
>>>>> -
>>>>> -       fp->bpf_func = (void *)ctx.target;
>>>>>    out:
>>>>>           kfree(ctx.offsets);
>>>>> +
>>>>> +       *out_ctx = ctx;
>>>>>           return;
>>>>
>>>> This part of the patch, in combination with 79617801e "filter: bpf_jit_comp:
>>>> refactor and unify BPF JIT image dump output" is now causing build errors
>>>> in linux-next:
>>>>
>>>> arch/arm/net/bpf_jit_32.c: In function '__bpf_jit_compile':
>>>> arch/arm/net/bpf_jit_32.c:930:16: error: 'fp' undeclared (first use in this function)
>>>>      bpf_jit_dump(fp->len, alloc_size, 2, ctx.target);
>>>
>>> Thanks, I did this.  There may be a smarter way...
>>
>> I think also seccomp_jit_compile() would need this change then, otherwise the build
>> with CONFIG_SECCOMP_FILTER_JIT might break.
>
> urgh, that tears it.
>
>> I can fix this up for you if not already applied. I presume it's against
>> linux-next tree?
>
> Yup, please send something.

Patch is attached. However, I currently don't have an ARM toolchain at hand, so
uncompiled, untested.

@Nicolas, Xi (cc, ref: http://thread.gmane.org/gmane.linux.kernel/1481464):

If there is someday support for other archs as well, it would be nice if we
do not have each time duplicated seccomp_jit_compile() etc functions in each
JIT implementation, i.e. because they do basically the same. So follow-up
{fix,clean}up is appreciated.

Also, I find it a bit weird that seccomp_filter_get_len() and some other
_one-line_ functions from kernel/seccomp.c are not placed into the
corresponding header file as inlines.

View attachment "0001-ARM-bpf_jit-seccomp-filtering-fixup-merge-conflict.patch" of type "text/x-patch" (1669 bytes)