linux-kernel - Re: perf test BPF subtest bpf-prologue test fails on s390x

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Message-Id: <baf74c0b-56a8-c67b-6376-e8bdebf30636@linux.vnet.ibm.com>
Date:   Fri, 11 Aug 2017 13:13:08 +0200
From:   Thomas-Mich Richter <tmricht@...ux.vnet.ibm.com>
To:     "Wangnan (F)" <wangnan0@...wei.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Hendrik Brueckner <brueckner@...ux.vnet.ibm.com>,
        Zefan Li <lizefan@...wei.com>,
        linux-perf-users@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: perf test BPF subtest bpf-prologue test fails on s390x

On 08/11/2017 11:57 AM, Wangnan (F) wrote:
> 
> 
> On 2017/8/11 17:17, Thomas-Mich Richter wrote:
>> On 08/11/2017 07:19 AM, Wangnan (F) wrote:


[....]

> Your analysis is correct.
> 
>>
>> Maybe the solution is to add an endianness convertion into the gen_read_mem()
>> function.
> 
> That means alert the prologue. We can utilize the size field in BPF_LDX_MEM.
> 
> Could you please try this patch:
> 
> diff --git a/tools/perf/util/bpf-prologue.c b/tools/perf/util/bpf-prologue.c
> index 6cdbee1..aadbda4 100644
> --- a/tools/perf/util/bpf-prologue.c
> +++ b/tools/perf/util/bpf-prologue.c
> @@ -258,7 +258,7 @@ gen_prologue_slowpath(struct bpf_insn_pos *pos,
> 
>         /* Final pass: read to registers */
>         for (i = 0; i < nargs; i++)
> -               ins(BPF_LDX_MEM(BPF_DW, BPF_PROLOGUE_START_ARG_REG + i,
> +               ins(BPF_LDX_MEM(BPF_W, BPF_PROLOGUE_START_ARG_REG + i,
>                                 BPF_REG_FP, -BPF_REG_SIZE * (i + 1)), pos);
> 
>         ins(BPF_JMP_IMM(BPF_JA, BPF_REG_0, 0, JMP_TO_SUCCESS_CODE), pos);
> 
> 
> On your platform and check if the value of f_mode is correct?
> 
> NOTE: 64 bit load becomes incorrect after applying this patch. I want to make sure
> the behavior of 32 bit BPF load instruction works correct on big endian machine.
> 
> Thank you.
> 

This patch solves the issue with the first parameter. Now I see the correct
value of f_mode member of struct-file.
As you said the other loads are wrong. Here is the output of the 
trace:

           perf-13438 [000] d..2  2102.392312: : f_mode 6001f offset:0 orig:0
            perf-13438 [000] d..2  2102.392414: : f_mode 2001d offset:0 orig:0
            perf-13438 [000] d..2  2102.392440: : f_mode 2001d offset:0 orig:0
            perf-13438 [000] d..2  2102.392453: : f_mode 6001f offset:0 orig:0

PS: When I ran this test I undid the changes to tests/bpf-test-script-prologue.c.
It was in its original state when this test was executed.


-- 
Thomas Richter, Dept 3303, IBM LTC Boeblingen Germany
--
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