Re: [PATCH v6 3/5] samples: ftrace: Save required argument registers in sample trampolines

Mark Rutland
2023-04-06T10:23:25Z

On Wed, Apr 05, 2023 at 08:02:48PM +0200, Florent Revest wrote:
> The ftrace-direct-too sample traces the handle_mm_fault function whose
> signature changed since the introduction of the sample. Since:
> commit bce617edecad ("mm: do page fault accounting in handle_mm_fault")
> handle_mm_fault now has 4 arguments. Therefore, the sample trampoline
> should save 4 argument registers.
>
> s390 saves all argument registers already so it does not need a change
> but x86_64 needs an extra push and pop.
>
> This also evolves the signature of the tracing function to make it
> mirror the signature of the traced function.
>
> Signed-off-by: Florent Revest <revest@chromium.org>

Reviewed-by: Mark Rutland <mark.rutland@arm.com>

Thanks for this!

Mark.

> ---
> samples/ftrace/ftrace-direct-too.c | 14 ++++++++------
> 1 file changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/samples/ftrace/ftrace-direct-too.c b/samples/ftrace/ftrace-direct-too.c
> index f28e7b99840f..71ed4ee8cb4a 100644
> --- a/samples/ftrace/ftrace-direct-too.c
> +++ b/samples/ftrace/ftrace-direct-too.c
> @@ -5,14 +5,14 @@
> #include <linux/ftrace.h>
> #include <asm/asm-offsets.h>
>
> -extern void my_direct_func(struct vm_area_struct *vma,
> - unsigned long address, unsigned int flags);
> +extern void my_direct_func(struct vm_area_struct *vma, unsigned long address,
> + unsigned int flags, struct pt_regs *regs);
>
> -void my_direct_func(struct vm_area_struct *vma,
> - unsigned long address, unsigned int flags)
> +void my_direct_func(struct vm_area_struct *vma, unsigned long address,
> + unsigned int flags, struct pt_regs *regs)
> {
> - trace_printk("handle mm fault vma=%p address=%lx flags=%x\n",
> - vma, address, flags);
> + trace_printk("handle mm fault vma=%p address=%lx flags=%x regs=%p\n",
> + vma, address, flags, regs);
> }
>
> extern void my_tramp(void *);
> @@ -34,7 +34,9 @@ asm (
> " pushq %rdi\n"
> " pushq %rsi\n"
> " pushq %rdx\n"
> +" pushq %rcx\n"
> " call my_direct_func\n"
> +" popq %rcx\n"
> " popq %rdx\n"
> " popq %rsi\n"
> " popq %rdi\n"
> --
> 2.40.0.577.gac1e443424-goog
>