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Message-ID: <1514c929-5a98-0e58-e038-9bb4537d5189@yadro.com>
Date:   Tue, 17 Jan 2023 16:16:54 +0300
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Subject: Re: [PATCH -next V7 6/7] samples: ftrace: Add riscv support for
 SAMPLE_FTRACE_DIRECT[_MULTI]
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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>
From:   Evgenii Shatokhin <e.shatokhin@yadro.com>
In-Reply-To: <CAAYs2=jj2uiF3P_B1tXQTHdYOmcN7dRcMyPx2tW2kg4QWvq3Lg@mail.gmail.com>
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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.

> 
> 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