Re: [PATCH bpf-next v2] [tools/bpf] workaround a verifier failure for test_progs

From: Yonghong Song <yhs@fb.com>
To: Ma Xinjian <max.xinjian@intel.com>, <ast@fb.com>,
	<bpf@vger.kernel.org>, <daniel@iogearbox.net>,
	<kernel-team@fb.com>
Cc: "Li, Philip" <philip.li@intel.com>
Subject: Re: [PATCH bpf-next v2] [tools/bpf] workaround a verifier failure for test_progs
Date: Mon, 27 Apr 2020 23:13:10 -0700	[thread overview]
Message-ID: <1b8051db-20af-73ab-179e-8818bee7c7ee@fb.com> (raw)
In-Reply-To: <4c14c01e-be39-817b-ca8c-200690ac4caf@intel.com>

On 4/27/20 7:56 PM, Ma Xinjian wrote:
> Hi Yonghong.
> 
> During our team's test, we find a similar issue. when run test_sysctl of 
> bpf, we met error:
> 
> ```
> 
> libbpf: -- END LOG --
> libbpf: failed to load program 'cgroup/sysctl'
> libbpf: failed to load object './test_sysctl_prog.o'
> (test_sysctl.c:1490: errno: Permission denied) >>> Loading program 
> (./test_sysctl_prog.o) error.
> 
> ```
> 
> Testing env: "Debian GNU/Linux 9 (stretch)"
> 
> kernel: 5.6 5.7-rc1 5.7-rc2 5.7-rc3
> 
> clang/llvm version: v11.0.0.
> 
> we have tested a log of commits, following commits are part of them
> 
> drwxrwxr-x 2 root root  1 Apr 28 07:01 
> f30416fdde922eaa655934e050026930fefbd260
> drwxrwxr-x 2 root root  2 Apr 26 11:38 
> 10bc12588dac532fad044b2851dde8e7b9121e88
> drwxrwxr-x 2 root root  1 Apr 26 07:01 
> 969e7edd88ceb4791eb1cac22828290f0ae30b3d
> drwxrwxr-x 2 root root  1 Apr 23 13:51 
> bbf386f02b05db017fda66875cc5edef70779244
> drwxrwxr-x 2 root root  1 Apr 22 10:01 
> 2de52422acf04662b45599f77c14ce1b2cec2b81
> drwxrwxr-x 2 root root  1 Apr 21 07:07 
> a9b137f9ffba8cb25dfd7dd1fb613e8aac121b37
> drwxrwxr-x 2 root root  1 Apr 17 07:01 
> 40d139c620f83509fe18acbff5ec358298e99def
> 
> drwxrwxr-x 2 root root  1 Apr 16 07:02 
> bee6c234ed28ae7349cb83afa322dfd8394590ee
> 
> 
> And I have tested, If I add following patch like you did, test_sysctl pass:
> 
> diff --git a/tools/testing/selftests/bpf/progs/test_sysctl_prog.c 
> b/tools/testing/selftests/bpf/progs/test_sysctl_prog.c
> index 2d0b0b82a78a..8e3da8d2e7c9 100644
> --- a/tools/testing/selftests/bpf/progs/test_sysctl_prog.c
> +++ b/tools/testing/selftests/bpf/progs/test_sysctl_prog.c
> @@ -45,7 +45,10 @@ int sysctl_tcp_mem(struct bpf_sysctl *ctx)
>          unsigned long tcp_mem[3] = {0, 0, 0};
>          char value[MAX_VALUE_STR_LEN];
>          unsigned char i, off = 0;
> -       int ret;
> +      /* a workaround to prevent compiler from generating
> +      * codes verifier cannot handle yet.
> +      */
> +      volatile int ret;
> 
>          if (ctx->write)
>                  return 0;

Right. This is related to alu32 mode. The detailed description
https://lore.kernel.org/bpf/20191107170045.2503480-1-yhs@fb.com/

We are still working on this, either a verifier solution or a compiler 
workaround.

> 
> root@vm-snb-15 
> /usr/src/perf_selftests-x86_64-rhel-7.6-kselftests-6a8b55ed4056ea5559ebe4f6a4b247f627870d4c/tools/testing/selftests/bpf# 
> ./test_sysctl
> 
> ...
> 
>   Summary: 40 PASSED, 0 FAILED
> 