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: <Zw7SkmEaz730uVbL@x1>
Date: Tue, 15 Oct 2024 17:37:38 -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 15, 2024 at 04:58:56PM -0300, Arnaldo Carvalho de Melo wrote:
> So I'm trying adding extra bounds checking, marking the index as
> volatile, adding compiler barriers, etc, all the fun with the verifier,
> but got distracted with other stuff, coming back to this now.
 
> Ok, the following seems to do the trick:
 
> [acme@...l-per740-01 perf-tools]$ git diff
> diff --git a/tools/perf/util/bpf_skel/augmented_raw_syscalls.bpf.c b/tools/perf/util/bpf_skel/augmented_raw_syscalls.bpf.c
> index 3b30aa74a3ae..ef87a04ff8d0 100644
> --- a/tools/perf/util/bpf_skel/augmented_raw_syscalls.bpf.c
> +++ b/tools/perf/util/bpf_skel/augmented_raw_syscalls.bpf.c
> @@ -486,6 +486,7 @@ static int augment_sys_enter(void *ctx, struct syscall_enter_args *args)
>                                 augmented = true;
>                 } else if (size < 0 && size >= -6) { /* buffer */
>                         index = -(size + 1);
> +                       index &= 7; // To satisfy the bounds checking with the verifier in some kernels
>                         aug_size = args->args[index];
>  
>                         if (aug_size > TRACE_AUG_MAX_BUF)
> 
> I'll now test it without Howard's patch to see if it fixes the RHEL8 +
> clang 17 case.

It works with this one-liner + the simplified patch from Howard and also
on this other system (RHEL9), as well as with Fedora 40, it would be
nice if someone could test with clang 16 and report back the version of
the kernel tested as well as the distro name/release, that way I can try
to get my hands on such as system and test there as well.

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
4e21679eb81b5f0d perf trace: The return from 'write' isn't a pid
2d2314d4b09b5ed9 tools headers UAPI: Sync linux/const.h with the kernel headers
⬢[acme@...lbox perf-tools]$

[root@...e ~]# uname -a
Linux nine 5.14.0-427.31.1.el9_4.x86_64 #1 SMP PREEMPT_DYNAMIC Fri Aug 9 14:06:03 EDT 2024 x86_64 x86_64 x86_64 GNU/Linux
[root@...e ~]# perf trace -e *sleep* sleep 1.234567890
     0.000 (1234.742 ms): sleep/80014 clock_nanosleep(rqtp: 0x7ffc55b11240, rmtp: 0x7ffc55b11230)           = 0
[root@...e ~]# clang --version
clang version 17.0.6 (Red Hat, Inc. 17.0.6-5.el9)
Target: x86_64-redhat-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
[root@...e ~]#

- Arnaldo