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

From: Song Shuai
Date: Tue Jan 17 2023 - 04:35:05 EST

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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.

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
> >
> >
>
> Regards,
> Evgenii
>
>

--
Thanks,
Song

Next message: Mel Gorman: "Re: [PATCH v4] sched/fair: limit sched slice duration"
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In reply to: Evgenii Shatokhin: "Re: [PATCH -next V7 6/7] samples: ftrace: Add riscv support for SAMPLE_FTRACE_DIRECT[_MULTI]"
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