Re: [PATCH -next V7 6/7] samples: ftrace: Add riscv support for SAMPLE_FTRACE_DIRECT[_MULTI]

From: Song Shuai
Date: Tue Jan 17 2023 - 21:37:32 EST

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Evgenii Shatokhin <e.shatokhin@xxxxxxxxx> 于2023年1月17日周二 16:22写道：
>
> 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@xxxxxxxxx> 于2023年1月16日周一 14:30写道：
> >>
> >>>
> >>> Hi,
> >>>
> >>> On 12.01.2023 12:06, guoren@xxxxxxxxxx wrote:
> >>>> From: Song Shuai <suagrfillet@xxxxxxxxx>
> >>>>
> >>>> 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@xxxxxxxxx>
> >>>> Tested-by: Guo Ren <guoren@xxxxxxxxxx>
> >>>> Signed-off-by: Guo Ren <guoren@xxxxxxxxxx>
> >>>> ---
> >>>> 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.

Yes, you're right.

I added 'mv a0,t0' in front of `call my_direct_func` to pass the address of
traced function with mcount offset.

Here is the updated patch for your reference.
https://github.com/sugarfillet/linux/commit/95b174fb104dd970b982ee6fa19879393e229318

>
> >
> >>
> >> 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@xxxxxxxxx/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
>
>

--
Thanks,
Song

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