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From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Stanislav Fomichev <sdf@google.com>,
	Eduard Zingerman <eddyz87@gmail.com>, bpf <bpf@vger.kernel.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Andrii Nakryiko <andrii@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Martin KaFai Lau <martin.lau@linux.dev>,
	Kernel Team <kernel-team@fb.com>, Yonghong Song <yhs@fb.com>
Subject: Re: [PATCH bpf-next 00/43] First set of verifier/*.c migrated to inline assembly
Date: Mon, 27 Mar 2023 09:37:12 -0700	[thread overview]
Message-ID: <CAEf4BzYhNcgFZEr8pcUJAtPubwRwRJhO=VXBOAnYRntnnUfGtA@mail.gmail.com> (raw)
In-Reply-To: <CAEf4BzaYEpqNG_trRL=LOKBi7txBdWefLO-aktTb2Gb=1K1wDQ@mail.gmail.com>

On Mon, Mar 27, 2023 at 9:35 AM Andrii Nakryiko
<andrii.nakryiko@gmail.com> wrote:
>
> On Sun, Mar 26, 2023 at 8:57 PM Alexei Starovoitov
> <alexei.starovoitov@gmail.com> wrote:
> >
> > On Sun, Mar 26, 2023 at 8:16 PM Andrii Nakryiko
> > <andrii.nakryiko@gmail.com> wrote:
> > >
> > > On Sat, Mar 25, 2023 at 6:19 PM Alexei Starovoitov
> > > <alexei.starovoitov@gmail.com> wrote:
> > > >
> > > > On Sat, Mar 25, 2023 at 9:16 AM Stanislav Fomichev <sdf@google.com> wrote:
> > > > >
> > > > > >
> > > > > > It was my understanding from the RFC feedback that this "lighter" way
> > > > > > is preferable and we already have some tests written like that.
> > > > > > Don't have a strong opinion on this topic.
> > > > >
> > > > > Ack, I'm obviously losing a bunch of context here :-(
> > > > > I like coalescing better, but if the original suggestion was to use
> > > > > this lighter way, I'll keep that in mind while reviewing.
> > > >
> > > > I still prefer the clean look of the tests, so I've applied this set.
> > > >
> > > > But I'm not going to insist that this is the only style developers
> > > > should use moving forward.
> > > > Whoever prefers "" style can use it in the future tests.
> > >
> > > Great, because I found out in practice that inability to add comments
> > > to the manually written asm code is a pretty big limitation.
> >
> > What do you mean by "inability" ?
> > The comments can be added. See verifier_and.c
> >         r0 &= 0xFFFF1234;                               \
> >         /* Upper bits are unknown but AND above masks out 1 zero'ing
> > lower bits */\
> >         if w0 < 1 goto l0_%=;                           \
>
> My bad. I remembered that there were problems with comments in Eduards
> previous revision and concluded that they don't work in this
> "\-delimited mode". Especially that online documentation for GCC or
> Clang didn't explicitly say that they support /* */ comments in asm
> blocks (as far as I could google that).
>
> So now I know it's possible, thanks. I still find it very tedious to
> do manually, so I appreciate the flexibility in allowing to do
> ""-delimited style for new programs.
>
> Just to explain where I'm coming from. I took one asm program I have
> locally and converted it to a new style. It was tedious with all the
> tab alignment. Then I realized that one comment block uses too long
> lines and wanted to use vim to reformat them, and that doesn't work
> with those '\' delimiters at the end (I didn't have such a problem
> with the original style). So that turned into more tedious work. So
> for something that needs iteration and adjustments, ""-delimited style
> gives more flexibility. See below for reference.
>
> '#' comments are dangerous, btw, they silently ignore everything till
> the very end of asm block. No warning or error, just wrong and
> incomplete asm is generated, unfortunately.
>
>
> SEC("?raw_tp")
> __failure __log_level(2)
> __msg("XXX")
> __naked int subprog_result_precise(void)
> {
>         asm volatile (
>                 "r6 = 3;"
>                 /* pass r6 through r1 into subprog to get it back as r0;
>                  * this whole chain will have to be marked as precise later
>                  */
>                 "r1 = r6;"
>                 "call identity_subprog;"
>                 /* now use subprog's returned value (which is a
>                  * r6 -> r1 -> r0 chain), as index into vals array, forcing
>                  * all of that to be known precisely
>                  */
>                 "r0 *= 4;"
>                 "r1 = %[vals];"
>                 "r1 += r0;"
>                 /* here r0->r1->r6 chain is forced to be precise and has to be
>                  * propagated back to the beginning, including through the
>                  * subprog call
>                  */
>                 "r0 = *(u32 *)(r1 + 0);"
>                 "exit;"
>                 :
>                 : __imm_ptr(vals)
>                 : __clobber_common, "r6"
>         );
> }
>
> SEC("?raw_tp")
> __failure __log_level(2)
> __msg("XXX")
> __naked int subprog_result_precise2(void)
> {
>         asm volatile ("
>          \
>                 r6 = 3;
>          \
>                 /* pass r6 through r1 into subprog to get it back as
> r0;        \
>                  * this whole chain will have to be marked as precise
> later     \
>                  */
>          \
>                 r1 = r6;
>          \
>                 call identity_subprog;
>          \
>                 /* now use subprog's returned value (which is a
>          \
>                  * r6 -> r1 -> r0 chain), as index into vals array,
> forcing     \
>                  * all of that to be known precisely
>          \
>                  */
>          \
>                 r0 *= 4;
>          \
>                 r1 = %[vals];
>          \
>                 r1 += r0;
>          \
>                 /* here r0->r1->r6 chain is forced to be precise and
> has to be  \
>                  * propagated back to the beginning, including through
> the      \
>                  * subprog call
>          \
>                  */
>          \
>                 r0 = *(u32 *)(r1 + 0);
>          \
>                 exit;
>          \

Great, Gmail doesn't like this style as well :( Sorry for the visual noise.
>                 "
>                 :
>                 : __imm_ptr(vals)
>                 : __clobber_common, "r6"
>         );
> }

  reply	other threads:[~2023-03-27 16:37 UTC|newest]

Thread overview: 60+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-03-25  2:54 [PATCH bpf-next 00/43] First set of verifier/*.c migrated to inline assembly Eduard Zingerman
2023-03-25  2:54 ` [PATCH bpf-next 01/43] selftests/bpf: Report program name on parse_test_spec error Eduard Zingerman
2023-03-25  2:54 ` [PATCH bpf-next 02/43] selftests/bpf: __imm_insn & __imm_const macro for bpf_misc.h Eduard Zingerman
2023-03-25  2:54 ` [PATCH bpf-next 03/43] selftests/bpf: Unprivileged tests for test_loader.c Eduard Zingerman
2023-03-25  2:54 ` [PATCH bpf-next 04/43] selftests/bpf: Tests execution support " Eduard Zingerman
2023-03-25  2:54 ` [PATCH bpf-next 05/43] selftests/bpf: prog_tests entry point for migrated test_verifier tests Eduard Zingerman
2023-03-25  2:54 ` [PATCH bpf-next 06/43] selftests/bpf: verifier/and.c converted to inline assembly Eduard Zingerman
2023-03-25  2:54 ` [PATCH bpf-next 07/43] selftests/bpf: verifier/array_access.c " Eduard Zingerman
2023-03-25  2:54 ` [PATCH bpf-next 08/43] selftests/bpf: verifier/basic_stack.c " Eduard Zingerman
2023-03-25  2:54 ` [PATCH bpf-next 09/43] selftests/bpf: verifier/bounds_deduction.c " Eduard Zingerman
2023-03-25  2:54 ` [PATCH bpf-next 10/43] selftests/bpf: verifier/bounds_mix_sign_unsign.c " Eduard Zingerman
2023-03-25  2:54 ` [PATCH bpf-next 11/43] selftests/bpf: verifier/cfg.c " Eduard Zingerman
2023-03-25  2:54 ` [PATCH bpf-next 12/43] selftests/bpf: verifier/cgroup_inv_retcode.c " Eduard Zingerman
2023-03-25  2:54 ` [PATCH bpf-next 13/43] selftests/bpf: verifier/cgroup_skb.c " Eduard Zingerman
2023-03-25  2:54 ` [PATCH bpf-next 14/43] selftests/bpf: verifier/cgroup_storage.c " Eduard Zingerman
2023-03-25  2:54 ` [PATCH bpf-next 15/43] selftests/bpf: verifier/const_or.c " Eduard Zingerman
2023-03-25  2:54 ` [PATCH bpf-next 16/43] selftests/bpf: verifier/ctx_sk_msg.c " Eduard Zingerman
2023-03-25  2:54 ` [PATCH bpf-next 17/43] selftests/bpf: verifier/direct_stack_access_wraparound.c " Eduard Zingerman
2023-03-25  2:54 ` [PATCH bpf-next 18/43] selftests/bpf: verifier/div0.c " Eduard Zingerman
2023-03-25  2:55 ` [PATCH bpf-next 19/43] selftests/bpf: verifier/div_overflow.c " Eduard Zingerman
2023-03-25  2:55 ` [PATCH bpf-next 20/43] selftests/bpf: verifier/helper_access_var_len.c " Eduard Zingerman
2023-03-25  2:55 ` [PATCH bpf-next 21/43] selftests/bpf: verifier/helper_packet_access.c " Eduard Zingerman
2023-03-25  2:55 ` [PATCH bpf-next 22/43] selftests/bpf: verifier/helper_restricted.c " Eduard Zingerman
2023-03-25  2:55 ` [PATCH bpf-next 23/43] selftests/bpf: verifier/helper_value_access.c " Eduard Zingerman
2023-03-25  2:55 ` [PATCH bpf-next 24/43] selftests/bpf: verifier/int_ptr.c " Eduard Zingerman
2023-03-25  2:55 ` [PATCH bpf-next 25/43] selftests/bpf: verifier/ld_ind.c " Eduard Zingerman
2023-03-25  2:55 ` [PATCH bpf-next 26/43] selftests/bpf: verifier/leak_ptr.c " Eduard Zingerman
2023-03-25  2:55 ` [PATCH bpf-next 27/43] selftests/bpf: verifier/map_ptr.c " Eduard Zingerman
2023-03-25  2:55 ` [PATCH bpf-next 28/43] selftests/bpf: verifier/map_ret_val.c " Eduard Zingerman
2023-03-25  2:55 ` [PATCH bpf-next 29/43] selftests/bpf: verifier/masking.c " Eduard Zingerman
2023-03-25  2:55 ` [PATCH bpf-next 30/43] selftests/bpf: verifier/meta_access.c " Eduard Zingerman
2023-03-25  2:55 ` [PATCH bpf-next 31/43] selftests/bpf: verifier/raw_stack.c " Eduard Zingerman
2023-03-25  2:55 ` [PATCH bpf-next 32/43] selftests/bpf: verifier/raw_tp_writable.c " Eduard Zingerman
2023-03-25  2:55 ` [PATCH bpf-next 33/43] selftests/bpf: verifier/ringbuf.c " Eduard Zingerman
2023-03-25  2:55 ` [PATCH bpf-next 34/43] selftests/bpf: verifier/spill_fill.c " Eduard Zingerman
2023-03-25  2:55 ` [PATCH bpf-next 35/43] selftests/bpf: verifier/stack_ptr.c " Eduard Zingerman
2023-03-25  2:55 ` [PATCH bpf-next 36/43] selftests/bpf: verifier/uninit.c " Eduard Zingerman
2023-03-25  2:55 ` [PATCH bpf-next 37/43] selftests/bpf: verifier/value_adj_spill.c " Eduard Zingerman
2023-03-25  2:55 ` [PATCH bpf-next 38/43] selftests/bpf: verifier/value.c " Eduard Zingerman
2023-03-25  2:55 ` [PATCH bpf-next 39/43] selftests/bpf: verifier/value_or_null.c " Eduard Zingerman
2023-03-25  2:55 ` [PATCH bpf-next 40/43] selftests/bpf: verifier/var_off.c " Eduard Zingerman
2023-03-25  2:55 ` [PATCH bpf-next 41/43] selftests/bpf: verifier/xadd.c " Eduard Zingerman
2023-03-25  2:55 ` [PATCH bpf-next 42/43] selftests/bpf: verifier/xdp.c " Eduard Zingerman
2023-03-25  3:23 ` [PATCH bpf-next 00/43] First set of verifier/*.c migrated " Stanislav Fomichev
2023-03-25 12:20   ` Eduard Zingerman
2023-03-25 16:16     ` Stanislav Fomichev
2023-03-26  1:19       ` Alexei Starovoitov
2023-03-27  3:15         ` Andrii Nakryiko
2023-03-27  3:57           ` Alexei Starovoitov
2023-03-27 11:26             ` Eduard Zingerman
2023-03-27 16:35             ` Andrii Nakryiko
2023-03-27 16:37               ` Andrii Nakryiko [this message]
2023-03-26  1:32 ` patchwork-bot+netdevbpf
2023-03-28  3:48 ` Daniel Borkmann
2023-03-28 21:52   ` Eduard Zingerman
2023-03-28 22:24     ` Andrii Nakryiko
2023-03-28 22:38       ` Eduard Zingerman
2023-03-28 23:31         ` Alexei Starovoitov
2023-03-29  0:11           ` Andrii Nakryiko
2023-03-29  0:07         ` Andrii Nakryiko

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