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Message-ID: <7c85f9d8-458d-6881-ffbe-4f5c6384e35e@yadro.com>
Date: Tue, 17 Jan 2023 19:22:30 +0300
From: Evgenii Shatokhin <e.shatokhin@...ro.com>
To: Song Shuai <suagrfillet@...il.com>
CC: <guoren@...nel.org>, <linux-riscv@...ts.infradead.org>,
<linux-kernel@...r.kernel.org>, <anup@...infault.org>,
<paul.walmsley@...ive.com>, <palmer@...belt.com>,
<conor.dooley@...rochip.com>, <heiko@...ech.de>,
<rostedt@...dmis.org>, <mhiramat@...nel.org>, <jolsa@...hat.com>,
<bp@...e.de>, <jpoimboe@...nel.org>, <andy.chiu@...ive.com>,
<linux@...ro.com>
Subject: Re: [PATCH -next V7 6/7] samples: ftrace: Add riscv support for
SAMPLE_FTRACE_DIRECT[_MULTI]
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@...ro.com> 于2023年1月16日周一 14:30写道：
>>
>>>
>>> Hi,
>>>
>>> On 12.01.2023 12:06, guoren@...nel.org wrote:
>>>> From: Song Shuai <suagrfillet@...il.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@...il.com>
>>>> Tested-by: Guo Ren <guoren@...nel.org>
>>>> Signed-off-by: Guo Ren <guoren@...nel.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
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