linux-kernel - Re: [PATCH v2 0/2] perf trace: Fix support for the new BPF feature in clang 12

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Message-ID: <ZxkKnIaz6QaIC4VN@x1>
Date: Wed, 23 Oct 2024 11:39:24 -0300
From: Arnaldo Carvalho de Melo <acme@...nel.org>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Song Liu <songliubraving@...com>, Howard Chu <howardchu95@...il.com>,
	Andrea Righi <andrea.righi@...ux.dev>, peterz@...radead.org,
	mingo@...hat.com, mark.rutland@....com,
	alexander.shishkin@...ux.intel.com, jolsa@...nel.org,
	irogers@...gle.com, adrian.hunter@...el.com,
	kan.liang@...ux.intel.com, linux-perf-users@...r.kernel.org,
	linux-kernel@...r.kernel.org, james.clark@...aro.org,
	alan.maguire@...cle.com
Subject: Re: [PATCH v2 0/2] perf trace: Fix support for the new BPF feature
 in clang 12

On Tue, Oct 22, 2024 at 04:52:16PM -0700, Namhyung Kim wrote:
> On Tue, Oct 22, 2024 at 03:33:00PM -0300, Arnaldo Carvalho de Melo wrote:
> > On Tue, Oct 22, 2024 at 10:04:52AM -0700, Namhyung Kim wrote:
> > > On Wed, Oct 16, 2024 at 11:22:15AM -0300, Arnaldo Carvalho de Melo wrote:
> > > > On Tue, Oct 15, 2024 at 07:06:35PM -0700, Namhyung Kim wrote:
> > > > > On Tue, Oct 15, 2024 at 05:37:38PM -0300, Arnaldo Carvalho de Melo wrote:
> > > > > > On Tue, Oct 15, 2024 at 04:58:56PM -0300, Arnaldo Carvalho de Melo wrote:
> > > > > > Its all at:

> > > > > > https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools.git tmp.perf-tools

> > > > > > This is the current set of patches that when further tested will go to
> > > > > > Linus for v6.12:

> > > > > > ⬢[acme@...lbox perf-tools]$ git log --oneline torvalds/master..
> > > > > > ff14baa7a290bf42 (HEAD -> perf-tools, x1/perf-tools, perf-tools/tmp.perf-tools) perf trace augmented_raw_syscalls: Add more checks to pass the verifier
> > > > > > 46180bec048aad85 perf trace augmented_raw_syscalls: Add extra array index bounds checking to satisfy some BPF verifiers
> > > > > > 45d1aadac64869a2 perf build: Change the clang check back to 12.0.1

> > > > > Wouldn't it be better to have this change after fixing the verifier
> > > > > issues in the later commits?

> > > > I'm still testing it, this is a one-liner, so I think that the order in
> > > > which the patches are applied isn't important. Also Howard's patch (the
> > > > simplified one) doesn't clash with it.

> > > I'm afraid if it'd break git bisect by allowing old clang versions
> > > before the fix.

> > I can reorder the patches if you think it is interesting, but from the
> > extended set of tests I'm performing on different kernel and clang
> > version and in x86_64 and arm 64-bit, 32-bit and various distros, I'm
> > not sure bisection is an option for BPF programs at this stage 8-)

> Maybe.  But at least we can try our best. :)

That rhel8 verifier case was with clang 17 even, but whatever, see below
:-)

> > There, did it now it looks like this:
> > 
> > ⬢ [acme@...lbox perf-tools]$ git log --oneline torvalds/master..
> > 5d3a1b9ca3b1a059 (HEAD -> perf-tools) perf trace arm32: Fix iteration of syscall ids in syscalltbl->entries
> > 34d2358a24fb5963 perf trace augmented_raw_syscalls: Add more checks to pass the verifier
> > cdb84c31bd2813de perf trace augmented_raw_syscalls: Add extra array index bounds checking to satisfy some BPF verifiers
> > e5c1811c590c4312 perf build: Change the clang check back to 12.0.1
> > 39c6a356201ebbd7 perf trace: The return from 'write' isn't a pid
> > ab8aaab874c4aa37 tools headers UAPI: Sync linux/const.h with the kernel headers
> > ⬢ [acme@...lbox perf-tools]$

> > Is that what you meant?
 
> Nope, I'd like to have e5c1811c590c4312 after the verifier fixes:
 
>  34d2358a24fb5963 perf trace augmented_raw_syscalls: Add more checks to pass the verifier
>  cdb84c31bd2813de perf trace augmented_raw_syscalls: Add extra array index bounds checking to satisfy some BPF verifiers

Done:

⬢ [acme@...lbox perf-tools]$ git log --oneline torvalds/master..
d822ca29a4fc5278 (HEAD -> perf-tools) tools headers UAPI: Sync kvm headers with the kernel sources
5d35634ecc2d2c39 perf trace: Fix non-listed archs in the syscalltbl routines
7fbff3c0e085745b perf build: Change the clang check back to 12.0.1
395d38419f1853de perf trace augmented_raw_syscalls: Add more checks to pass the verifier
ecabac70ff919580 perf trace augmented_raw_syscalls: Add extra array index bounds checking to satisfy some BPF verifiers
39c6a356201ebbd7 perf trace: The return from 'write' isn't a pid
ab8aaab874c4aa37 tools headers UAPI: Sync linux/const.h with the kernel headers
⬢ [acme@...lbox perf-tools]$

- Arnaldo