linux-kernel - Re: [PATCH] perf test: Fix perf test 42

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Date:   Tue, 23 Mar 2021 15:06:32 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Thomas Richter <tmricht@...ux.ibm.com>
Cc:     linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        svens@...ux.ibm.com, gor@...ux.ibm.com, sumanthk@...ux.ibm.com,
        hca@...ux.ibm.com
Subject: Re: [PATCH] perf test: Fix perf test 42

Em Mon, Mar 22, 2021 at 01:53:39PM +0100, Thomas Richter escreveu:
> For some time now the perf test 42: BPF filter returns an error
> on bpf relocation subtest, at least on x86 and s390. This is caused by
> 
> commit d859900c4c56 ("bpf, libbpf: support global data/bss/rodata sections")
> 
> which introduces support for global variables in eBPF programs. At least
> for global variables defined static.
> 
> Perf test 42 checks that the eBPF relocation fails when the eBPF program
> contains a global variable. It returns OK when the eBPF program
> could not be loaded and FAILED otherwise.
> 
> With above commit the test logic for the eBPF relocation need to change:
> 1. The function prepare_bpf() now always succeeds, the eBPF program
>    compiled without errors and returns a valid object pointer instead of
>    NULL.
> 2. There is no kprobe named sys_write, it now named ksys_write.
> 3. The function do_test() now returns TEST_FAIL because function
>    parse_events_load_bpf_obj() can not execute the eBPF program. The
>    eBPF verifier complains on an invalid map pointer:
>       libbpf: load bpf program failed: Permission denied
>       libbpf: -- BEGIN DUMP LOG ---
>       libbpf:
>       0: (b7) r1 = 0
>       1: (63) *(u32 *)(r10 -4) = r1
>       last_idx 1 first_idx 0
>       regs=2 stack=0 before 0: (b7) r1 = 0
>       2: (63) *(u32 *)(r10 -8) = r1
>       3: (bf) r2 = r10
>       4: (07) r2 += -4
>       5: (bf) r3 = r10
>       6: (07) r3 += -8
>       7: (18) r1 = 0x380006ce000
>       9: (b7) r4 = 0
>       10: (85) call bpf_map_update_elem#2
>       R1 type=map_value expected=map_ptr
> 
> Fix this by added logic to handle the kernel verifier return code:
> 1. Add function myksys_write() to cope with successful compile.
> 2. Use kprobe ksys_write
> 3. Handle eBPF verifier error.
> 
> Output after:
>  42: BPF filter                          :
>  42.1: Basic BPF filtering               : Ok
>  42.2: BPF pinning                       : Ok
>  42.3: BPF prologue generation           : Ok
>  42.4: BPF relocation checker            : Failed
>  #
> 
> Output after:
>  # ./perf test -F 42
>  42: BPF filter                          :
>  42.1: Basic BPF filtering               : Ok
>  42.2: BPF pinning                       : Ok
>  42.3: BPF prologue generation           : Ok
>  42.4: BPF relocation checker            : Ok
>  #
> 
> Signed-off-by: Thomas Richter <tmricht@...ux.ibm.com>
> ---
>  tools/perf/tests/bpf-script-test-relocation.c |  4 ++--
>  tools/perf/tests/bpf.c                        | 11 +++++++++++
>  2 files changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/perf/tests/bpf-script-test-relocation.c b/tools/perf/tests/bpf-script-test-relocation.c
> index 74006e4b2d24..f8f8176ad4d1 100644
> --- a/tools/perf/tests/bpf-script-test-relocation.c
> +++ b/tools/perf/tests/bpf-script-test-relocation.c
> @@ -34,8 +34,8 @@ struct bpf_map_def SEC("maps") my_table = {
>  
>  int this_is_a_global_val;
>  
> -SEC("func=sys_write")
> -int bpf_func__sys_write(void *ctx)
> +SEC("func=ksys_write")
> +int bpf_func__ksys_write(void *ctx)
>  {
>  	int key = 0;
>  	int value = 0;
> diff --git a/tools/perf/tests/bpf.c b/tools/perf/tests/bpf.c
> index f57e075b0ed2..d60ef9472d3d 100644
> --- a/tools/perf/tests/bpf.c
> +++ b/tools/perf/tests/bpf.c
> @@ -59,6 +59,11 @@ static int llseek_loop(void)
>  
>  #endif
>  
> +static int myksys_write(void)
> +{
> +	return 0;
> +}
> +
>  static struct {
>  	enum test_llvm__testcase prog_id;
>  	const char *desc;
> @@ -105,6 +110,7 @@ static struct {
>  		.name		  = "[bpf_relocation_test]",
>  		.msg_compile_fail = "fix 'perf test LLVM' first",
>  		.msg_load_fail	  = "libbpf error when dealing with relocation",
> +		.target_func	  = &myksys_write,
>  	},
>  };
>  
> @@ -258,6 +264,11 @@ static int __test__bpf(int idx)
>  		ret = do_test(obj,
>  			      bpf_testcase_table[idx].target_func,
>  			      bpf_testcase_table[idx].expect_result);
> +		if (bpf_testcase_table[idx].prog_id == LLVM_TESTCASE_BPF_RELOCATION
> +		    && ret == TEST_FAIL) {
> +			ret = TEST_OK;
> +			goto out;
> +		}

At this point, if it doesn't matter if it fails or succeeds, just drop
this test case?

- Arnaldo

>  		if (ret != TEST_OK)
>  			goto out;
>  		if (bpf_testcase_table[idx].pin) {
> -- 
> 2.30.2
> 

-- 

- Arnaldo