Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <7c85f9d8-458d-6881-ffbe-4f5c6384e35e@yadro.com>
Date:   Tue, 17 Jan 2023 19:22:30 +0300
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.4.2
Subject: Re: [PATCH -next V7 6/7] samples: ftrace: Add riscv support for
 SAMPLE_FTRACE_DIRECT[_MULTI]
Content-Language: en-US
From:   Evgenii Shatokhin <e.shatokhin@yadro.com>
To:     Song Shuai <suagrfillet@gmail.com>
CC:     <guoren@kernel.org>, <linux-riscv@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>, <anup@brainfault.org>,
        <paul.walmsley@sifive.com>, <palmer@dabbelt.com>,
        <conor.dooley@microchip.com>, <heiko@sntech.de>,
        <rostedt@goodmis.org>, <mhiramat@kernel.org>, <jolsa@redhat.com>,
        <bp@suse.de>, <jpoimboe@kernel.org>, <andy.chiu@sifive.com>,
        <linux@yadro.com>
References: <20230112090603.1295340-1-guoren@kernel.org>
 <20230112090603.1295340-7-guoren@kernel.org>
 <a83dc6de-8fda-439d-b2dd-d05786e642eb@yadro.com>
 <CAAYs2=jj2uiF3P_B1tXQTHdYOmcN7dRcMyPx2tW2kg4QWvq3Lg@mail.gmail.com>
 <1514c929-5a98-0e58-e038-9bb4537d5189@yadro.com>
In-Reply-To: <1514c929-5a98-0e58-e038-9bb4537d5189@yadro.com>
Content-Type: text/plain; charset="UTF-8"; format=flowed
Content-Transfer-Encoding: 8bit
Precedence: bulk

On 17.01.2023 16:16, Evgenii Shatokhin wrote:
> Hi, Song,
> 
> On 17.01.2023 12:32, Song Shuai wrote:
>>
>> Hi, Evgenii:
>>
>> Evgenii Shatokhin <e.shatokhin@yadro.com> 于2023年1月16日周一 14:30写道：
>>
>>>
>>> Hi,
>>>
>>> On 12.01.2023 12:06, guoren@kernel.org wrote:
>>>> From: Song Shuai <suagrfillet@gmail.com>
>>>>
>>>> select HAVE_SAMPLE_FTRACE_DIRECT and HAVE_SAMPLE_FTRACE_DIRECT_MULTI
>>>> for ARCH_RV64I in arch/riscv/Kconfig. And add riscv asm code for
>>>> the ftrace-direct*.c files in samples/ftrace/.
>>>>
>>>> Signed-off-by: Song Shuai <suagrfillet@gmail.com>
>>>> Tested-by: Guo Ren <guoren@kernel.org>
>>>> Signed-off-by: Guo Ren <guoren@kernel.org>
>>>> ---
>>>>    arch/riscv/Kconfig                          |  2 ++
>>>>    samples/ftrace/ftrace-direct-modify.c       | 33 ++++++++++++++++++
>>>>    samples/ftrace/ftrace-direct-multi-modify.c | 37 
>>>> +++++++++++++++++++++
>>>>    samples/ftrace/ftrace-direct-multi.c        | 22 ++++++++++++
>>>>    samples/ftrace/ftrace-direct-too.c          | 26 +++++++++++++++
>>>>    samples/ftrace/ftrace-direct.c              | 22 ++++++++++++
>>>>    6 files changed, 142 insertions(+)
>>>
>>> The samples were built OK now, but ftrace-direct-multi and
>>> ftrace-direct-multi-modify report incorrect values of ip/pc it seems.
>>>
>>> I ran 'insmod ftrace-direct-multi.ko', waited a little and then checked
>>> the messages in the trace:
>>>
>>> #           TASK-PID     CPU#  |||||  TIMESTAMP  FUNCTION
>>> #              | |         |   |||||     |         |
>>>        migration/1-19      [001] .....  3858.532131: my_direct_func1: my
>>> direct func1 ip 0
>>>        migration/0-15      [000] d.s2.  3858.532136: my_direct_func1: my
>>> direct func1 ip ff60000001ba9600
>>>        migration/0-15      [000] d..2.  3858.532204: my_direct_func1: my
>>> direct func1 ip ff60000003334d00
>>>        migration/0-15      [000] .....  3858.532232: my_direct_func1: my
>>> direct func1 ip 0
>>>          rcu_sched-14      [001] .....  3858.532257: my_direct_func1: my
>>> direct func1 ip 0
>>>             insmod-415     [000] .....  3858.532270: my_direct_func1: my
>>> direct func1 ip 7fffffffffffffff
>>>             <idle>-0       [001] ..s1.  3858.539051: my_direct_func1: my
>>> direct func1 ip ff60000001ba9600
>>>             <idle>-0       [001] dns2.  3858.539124: my_direct_func1: my
>>> direct func1 ip ff60000001ba9600
>>>          rcu_sched-14      [001] .....  3858.539208: my_direct_func1: my
>>> direct func1 ip 0
>>> [...]
>>>
>>> If I understand it right, my_direct_func1() should print the address of
>>> some location in the code, probably - at the beginning of the traced
>>> functions.
>>>
>>> The printed values (0x0, 0x7fffffffffffffff, ...) are not valid code
>>> addresses.
>>>
>> The invalid code address is only printed by accessing the schedule()
>> function's first argument whose address stores in a0 register.
>> While schedule() actually has no parameter declared, so my_direct_func
>> just prints the a0 in the context of the schedule()'s caller and
>> the address maybe varies depending on the caller.
>>
>> I can't really understand why tracing the first argument of the
>> schedule() function, but it seems nonsense at this point.
> 
> The question is, what should be passed as the argument(s) of 
> my_direct_func() in this particular sample module. The kernel docs and 
> commit logs seem to contain no info on that.
> 
> With direct functions, I suppose, the trampoline can pass anything it 
> wants to my_direct_func(), not just the arguments of the traced function.
> 
> I'd check what these sample modules do on x86 and would try to match 
> that behaviour on RISC-V.

I have checked ftrace-direct-multi.ko and ftrace-direct-multi-modify.ko 
on 6.2-rc4 built for x86-64 - yes, ip/pc in the traced function should 
be passed to my_direct_func().

ftrace-direct-multi.ko:
#           TASK-PID     CPU#  |||||  TIMESTAMP  FUNCTION
#              | |         |   |||||     |         |
           insmod-10829   [000] d.h1.  1719.518535: my_direct_func: ip 
ffffffff87332f45 // wake_up_process+0x5
  rcu_tasks_kthre-11      [000] .....  1719.518696: my_direct_func: ip 
ffffffff8828d935 // schedule+0x5
           insmod-10829   [000] .....  1719.518708: my_direct_func: ip 
ffffffff8828d935
  systemd-journal-293     [001] .....  1719.518823: my_direct_func: ip 
ffffffff8828d935
          systemd-1       [000] .....  1719.519141: my_direct_func: ip 
ffffffff8828d935
           <idle>-0       [001] ..s1.  1719.521889: my_direct_func: ip 
ffffffff87332f45
           <idle>-0       [000] d.s2.  1719.521901: my_direct_func: ip 
ffffffff87332f45
      rcu_preempt-15      [001] .....  1719.521917: my_direct_func: ip 
ffffffff8828d935
[...]

The ip values are wake_up_process+0x5 and schedule+0x5, the locations 
where the execution of the traced functions resumes after the Ftrace 
trampoline has finished.

The results with ftrace-direct-multi-modify.ko are similar to that.

The samples look like a demonstration, that one can pass anything 
necessary to the handler in case of "direct" functions.

I suppose, the RISC-V-specific asm code in these two sample modules 
could be updated to pass the saved pc value to my_direct_func() in a0.

> 
>>
>> As for this patch, it just impls a simple mcount (direct_caller) to
>> trace kernel functions, and basically saves the necessary ABI,
>> call the tracing function, and restores the ABI, just like other 
>> arches do.
>> so It shouldn't be blamed.
>>
>> I started an independent patch to replace schedule with kick_process
>> to make these samples more reasonable. And It has no conflict with the
>> current patch, so we can go on.
>>
>> Link: 
>> https://lore.kernel.org/linux-kernel/20230117091101.3669996-1-suagrfillet@gmail.com/T/#u
>>
>>> The same issue is with ftrace-direct-multi-modify.ko.
>>>
>>> Is anything missing here?
>>>
>>>>
>>>> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
>>>> index 307a9f413edd..e944af44f681 100644
>>>> --- a/arch/riscv/Kconfig
>>>> +++ b/arch/riscv/Kconfig
>>>> @@ -112,6 +112,8 @@ config RISCV
>>>>           select HAVE_POSIX_CPU_TIMERS_TASK_WORK
>>>>           select HAVE_REGS_AND_STACK_ACCESS_API
>>>>           select HAVE_FUNCTION_ARG_ACCESS_API
>>>> +       select HAVE_SAMPLE_FTRACE_DIRECT
>>>> +       select HAVE_SAMPLE_FTRACE_DIRECT_MULTI
>>>>           select HAVE_STACKPROTECTOR
>>>>           select HAVE_SYSCALL_TRACEPOINTS
>>>>           select HAVE_RSEQ
>>>> diff --git a/samples/ftrace/ftrace-direct-modify.c 
>>>> b/samples/ftrace/ftrace-direct-modify.c
>>>> index de5a0f67f320..be7bf472c3c7 100644
>>>> --- a/samples/ftrace/ftrace-direct-modify.c
>>>> +++ b/samples/ftrace/ftrace-direct-modify.c
>>>> @@ -23,6 +23,39 @@ extern void my_tramp2(void *);
>>>>
>>>>    static unsigned long my_ip = (unsigned long)schedule;
>>>>
>>>> +#ifdef CONFIG_RISCV
>>>> +
>>>> +asm (" .pushsection    .text, \"ax\", @progbits\n"
>>>> +"      .type           my_tramp1, @function\n"
>>>> +"      .globl          my_tramp1\n"
>>>> +"   my_tramp1:\n"
>>>> +"      addi sp,sp,-16\n"
>>>> +"      sd   t0,0(sp)\n"
>>>> +"      sd   ra,8(sp)\n"
>>>> +"      call my_direct_func1\n"
>>>> +"      ld   t0,0(sp)\n"
>>>> +"      ld   ra,8(sp)\n"
>>>> +"      addi sp,sp,16\n"
>>>> +"      jr t0\n"
>>>> +"      .size           my_tramp1, .-my_tramp1\n"
>>>> +
>>>> +"      .type           my_tramp2, @function\n"
>>>> +"      .globl          my_tramp2\n"
>>>> +"   my_tramp2:\n"
>>>> +"      addi sp,sp,-16\n"
>>>> +"      sd   t0,0(sp)\n"
>>>> +"      sd   ra,8(sp)\n"
>>>> +"      call my_direct_func2\n"
>>>> +"      ld   t0,0(sp)\n"
>>>> +"      ld   ra,8(sp)\n"
>>>> +"      addi sp,sp,16\n"
>>>> +"      jr t0\n"
>>>> +"      .size           my_tramp2, .-my_tramp2\n"
>>>> +"      .popsection\n"
>>>> +);
>>>> +
>>>> +#endif /* CONFIG_RISCV */
>>>> +
>>>>    #ifdef CONFIG_X86_64
>>>>
>>>>    #include <asm/ibt.h>
>>>> diff --git a/samples/ftrace/ftrace-direct-multi-modify.c 
>>>> b/samples/ftrace/ftrace-direct-multi-modify.c
>>>> index d52370cad0b6..10884bf418f7 100644
>>>> --- a/samples/ftrace/ftrace-direct-multi-modify.c
>>>> +++ b/samples/ftrace/ftrace-direct-multi-modify.c
>>>> @@ -21,6 +21,43 @@ void my_direct_func2(unsigned long ip)
>>>>    extern void my_tramp1(void *);
>>>>    extern void my_tramp2(void *);
>>>>
>>>> +#ifdef CONFIG_RISCV
>>>> +
>>>> +asm (" .pushsection    .text, \"ax\", @progbits\n"
>>>> +"      .type           my_tramp1, @function\n"
>>>> +"      .globl          my_tramp1\n"
>>>> +"   my_tramp1:\n"
>>>> +"       addi sp,sp,-24\n"
>>>> +"       sd   a0,0(sp)\n"
>>>> +"       sd   t0,8(sp)\n"
>>>> +"       sd   ra,16(sp)\n"
>>>> +"       call my_direct_func1\n"
>>>> +"       ld   a0,0(sp)\n"
>>>> +"       ld   t0,8(sp)\n"
>>>> +"       ld   ra,16(sp)\n"
>>>> +"       addi sp,sp,24\n"
>>>> +"      jr t0\n"
>>>> +"      .size           my_tramp1, .-my_tramp1\n"
>>>> +
>>>> +"      .type           my_tramp2, @function\n"
>>>> +"      .globl          my_tramp2\n"
>>>> +"   my_tramp2:\n"
>>>> +"       addi sp,sp,-24\n"
>>>> +"       sd   a0,0(sp)\n"
>>>> +"       sd   t0,8(sp)\n"
>>>> +"       sd   ra,16(sp)\n"
>>>> +"       call my_direct_func2\n"
>>>> +"       ld   a0,0(sp)\n"
>>>> +"       ld   t0,8(sp)\n"
>>>> +"       ld   ra,16(sp)\n"
>>>> +"       addi sp,sp,24\n"
>>>> +"      jr t0\n"
>>>> +"      .size           my_tramp2, .-my_tramp2\n"
>>>> +"      .popsection\n"
>>>> +);
>>>> +
>>>> +#endif /* CONFIG_RISCV */
>>>> +
>>>>    #ifdef CONFIG_X86_64
>>>>
>>>>    #include <asm/ibt.h>
>>>> diff --git a/samples/ftrace/ftrace-direct-multi.c 
>>>> b/samples/ftrace/ftrace-direct-multi.c
>>>> index ec1088922517..a35bf43bf6d7 100644
>>>> --- a/samples/ftrace/ftrace-direct-multi.c
>>>> +++ b/samples/ftrace/ftrace-direct-multi.c
>>>> @@ -16,6 +16,28 @@ void my_direct_func(unsigned long ip)
>>>>
>>>>    extern void my_tramp(void *);
>>>>
>>>> +#ifdef CONFIG_RISCV
>>>> +
>>>> +asm ("       .pushsection    .text, \"ax\", @progbits\n"
>>>> +"       .type           my_tramp, @function\n"
>>>> +"       .globl          my_tramp\n"
>>>> +"   my_tramp:\n"
>>>> +"       addi sp,sp,-24\n"
>>>> +"       sd   a0,0(sp)\n"
>>>> +"       sd   t0,8(sp)\n"
>>>> +"       sd   ra,16(sp)\n"
>>>> +"       call my_direct_func\n"
>>>> +"       ld   a0,0(sp)\n"
>>>> +"       ld   t0,8(sp)\n"
>>>> +"       ld   ra,16(sp)\n"
>>>> +"       addi sp,sp,24\n"
>>>> +"       jr t0\n"
>>>> +"       .size           my_tramp, .-my_tramp\n"
>>>> +"       .popsection\n"
>>>> +);
>>>> +
>>>> +#endif /* CONFIG_RISCV */
>>>> +
>>>>    #ifdef CONFIG_X86_64
>>>>
>>>>    #include <asm/ibt.h>
>>>> diff --git a/samples/ftrace/ftrace-direct-too.c 
>>>> b/samples/ftrace/ftrace-direct-too.c
>>>> index e13fb59a2b47..3b62e33c2e6d 100644
>>>> --- a/samples/ftrace/ftrace-direct-too.c
>>>> +++ b/samples/ftrace/ftrace-direct-too.c
>>>> @@ -18,6 +18,32 @@ void my_direct_func(struct vm_area_struct *vma,
>>>>
>>>>    extern void my_tramp(void *);
>>>>
>>>> +#ifdef CONFIG_RISCV
>>>> +
>>>> +asm ("       .pushsection    .text, \"ax\", @progbits\n"
>>>> +"       .type           my_tramp, @function\n"
>>>> +"       .globl          my_tramp\n"
>>>> +"   my_tramp:\n"
>>>> +"       addi sp,sp,-40\n"
>>>> +"       sd   a0,0(sp)\n"
>>>> +"       sd   a1,8(sp)\n"
>>>> +"       sd   a2,16(sp)\n"
>>>> +"       sd   t0,24(sp)\n"
>>>> +"       sd   ra,32(sp)\n"
>>>> +"       call my_direct_func\n"
>>>> +"       ld   a0,0(sp)\n"
>>>> +"       ld   a1,8(sp)\n"
>>>> +"       ld   a2,16(sp)\n"
>>>> +"       ld   t0,24(sp)\n"
>>>> +"       ld   ra,32(sp)\n"
>>>> +"       addi sp,sp,40\n"
>>>> +"       jr t0\n"
>>>> +"       .size           my_tramp, .-my_tramp\n"
>>>> +"       .popsection\n"
>>>> +);
>>>> +
>>>> +#endif /* CONFIG_RISCV */
>>>> +
>>>>    #ifdef CONFIG_X86_64
>>>>
>>>>    #include <asm/ibt.h>
>>>> diff --git a/samples/ftrace/ftrace-direct.c 
>>>> b/samples/ftrace/ftrace-direct.c
>>>> index 1f769d0db20f..2cfe5a7d2d70 100644
>>>> --- a/samples/ftrace/ftrace-direct.c
>>>> +++ b/samples/ftrace/ftrace-direct.c
>>>> @@ -15,6 +15,28 @@ void my_direct_func(struct task_struct *p)
>>>>
>>>>    extern void my_tramp(void *);
>>>>
>>>> +#ifdef CONFIG_RISCV
>>>> +
>>>> +asm ("       .pushsection    .text, \"ax\", @progbits\n"
>>>> +"       .type           my_tramp, @function\n"
>>>> +"       .globl          my_tramp\n"
>>>> +"   my_tramp:\n"
>>>> +"       addi sp,sp,-24\n"
>>>> +"       sd   a0,0(sp)\n"
>>>> +"       sd   t0,8(sp)\n"
>>>> +"       sd   ra,16(sp)\n"
>>>> +"       call my_direct_func\n"
>>>> +"       ld   a0,0(sp)\n"
>>>> +"       ld   t0,8(sp)\n"
>>>> +"       ld   ra,16(sp)\n"
>>>> +"       addi sp,sp,24\n"
>>>> +"       jr t0\n"
>>>> +"       .size           my_tramp, .-my_tramp\n"
>>>> +"       .popsection\n"
>>>> +);
>>>> +
>>>> +#endif /* CONFIG_RISCV */
>>>> +
>>>>    #ifdef CONFIG_X86_64
>>>>
>>>>    #include <asm/ibt.h>
>>>> -- 
>>>> 2.36.1
>>
>> -- 
>> Thanks,
>> Song
>>
> 
> Regards,
> Evgenii