From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Jiong Wang <jiong.wang@netronome.com>
Cc: daniel@iogearbox.net, bpf@vger.kernel.org,
netdev@vger.kernel.org, oss-drivers@netronome.com
Subject: Re: [PATCH v6 bpf-next 01/17] bpf: verifier: offer more accurate helper function arg and return type
Date: Wed, 8 May 2019 10:51:13 -0700 [thread overview]
Message-ID: <20190508175111.hcbufw22mbksbpca@ast-mbp> (raw)
In-Reply-To: <87mujx6m4n.fsf@netronome.com>
On Wed, May 08, 2019 at 03:45:12PM +0100, Jiong Wang wrote:
>
> I might be misunderstanding your points, please just shout if I am wrong.
>
> Suppose the following BPF code:
>
> unsigned helper(unsigned long long, unsigned long long);
> unsigned long long test(unsigned *a, unsigned int c)
> {
> unsigned int b = *a;
> c += 10;
> return helper(b, c);
> }
>
> We get the following instruction sequence by latest llvm
> (-O2 -mattr=+alu32 -mcpu=v3)
>
> test:
> 1: w1 = *(u32 *)(r1 + 0)
> 2: w2 += 10
> 3: call helper
> 4: exit
>
> Argument Types
> ===
> Now instruction 1 and 2 are sub-register defines, and instruction 3, the
> call, use them implicitly.
>
> Without the introduction of the new ARG_CONST_SIZE32 and
> ARG_CONST_SIZE32_OR_ZERO, we don't know what should be done with w1 and
> w2, zero-extend them should be fine for all cases, but could resulting in a
> few unnecessary zero-extension inserted.
I don't think we're on the same page.
The argument type is _const_.
In the example above they are not _const_.
>
> And that why I introduce these new argument types, without them, there
> could be more than 10% extra zext inserted on benchmarks like bpf_lxc.
10% extra ? so be it.
We're talking past each other here.
I agree with your optimization goal, but I think you're missing
the safety concerns I'm trying to explain.
>
> But for helper functions, they are done by native code which may not follow
> this convention. For example, on arm32, calling helper functions are just
> jump to and execute native code. And if the helper returns u32, it just set
> r0, no clearing of r1 which is the high 32-bit in the register pair
> modeling eBPF R0.
it's arm32 bug then. All helpers _must_ return 64-bit back to bpf prog
and _must_ accept 64-bit from bpf prog.
next prev parent reply other threads:[~2019-05-08 17:51 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-03 10:42 [PATCH v6 bpf-next 00/17] bpf: eliminate zero extensions for sub-register writes Jiong Wang
2019-05-03 10:42 ` [PATCH v6 bpf-next 01/17] bpf: verifier: offer more accurate helper function arg and return type Jiong Wang
2019-05-06 13:57 ` Daniel Borkmann
2019-05-06 22:25 ` Jiong Wang
2019-05-08 11:12 ` Jiong Wang
2019-05-06 15:50 ` Alexei Starovoitov
2019-05-08 14:45 ` Jiong Wang
2019-05-08 17:51 ` Alexei Starovoitov [this message]
2019-05-09 12:32 ` Jiong Wang
2019-05-09 17:31 ` Jiong Wang
2019-05-10 1:53 ` Alexei Starovoitov
2019-05-10 8:30 ` Jiong Wang
2019-05-10 20:10 ` Alexei Starovoitov
2019-05-10 21:59 ` Jiong Wang
2019-05-03 10:42 ` [PATCH v6 bpf-next 02/17] bpf: verifier: mark verified-insn with sub-register zext flag Jiong Wang
2019-05-06 13:49 ` Daniel Borkmann
2019-05-06 14:49 ` Daniel Borkmann
2019-05-06 22:14 ` Jiong Wang
2019-05-03 10:42 ` [PATCH v6 bpf-next 03/17] bpf: verifier: mark patched-insn " Jiong Wang
2019-05-03 10:42 ` [PATCH v6 bpf-next 04/17] bpf: introduce new alu insn BPF_ZEXT for explicit zero extension Jiong Wang
2019-05-06 15:57 ` Alexei Starovoitov
2019-05-06 23:19 ` Jiong Wang
2019-05-07 4:29 ` Jiong Wang
2019-05-07 4:40 ` Alexei Starovoitov
2019-05-03 10:42 ` [PATCH v6 bpf-next 05/17] bpf: verifier: insert BPF_ZEXT according to zext analysis result Jiong Wang
2019-05-03 10:42 ` [PATCH v6 bpf-next 06/17] bpf: introduce new bpf prog load flags "BPF_F_TEST_RND_HI32" Jiong Wang
2019-05-03 10:42 ` [PATCH v6 bpf-next 07/17] bpf: verifier: randomize high 32-bit when BPF_F_TEST_RND_HI32 is set Jiong Wang
2019-05-03 10:42 ` [PATCH v6 bpf-next 08/17] libbpf: add "prog_flags" to bpf_program/bpf_prog_load_attr/bpf_load_program_attr Jiong Wang
2019-05-03 10:42 ` [PATCH v6 bpf-next 09/17] selftests: bpf: adjust several test_verifier helpers for insn insertion Jiong Wang
2019-05-03 10:42 ` [PATCH v6 bpf-next 10/17] selftests: bpf: enable hi32 randomization for all tests Jiong Wang
2019-05-03 10:42 ` [PATCH v6 bpf-next 11/17] arm: bpf: eliminate zero extension code-gen Jiong Wang
2019-05-03 10:42 ` [PATCH v6 bpf-next 12/17] powerpc: " Jiong Wang
2019-05-03 10:42 ` [PATCH v6 bpf-next 13/17] s390: " Jiong Wang
2019-05-03 13:41 ` Heiko Carstens
2019-05-03 13:50 ` Eric Dumazet
2019-05-03 14:09 ` Jiong Wang
2019-05-03 10:42 ` [PATCH v6 bpf-next 14/17] sparc: " Jiong Wang
2019-05-03 10:42 ` [PATCH v6 bpf-next 15/17] x32: " Jiong Wang
2019-05-03 10:42 ` [PATCH v6 bpf-next 16/17] riscv: " Jiong Wang
2019-05-03 10:42 ` [PATCH v6 bpf-next 17/17] nfp: " Jiong Wang
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