Re: Anyone working on ftrace function graph support on ARM?

Frederic Weisbecker
2009-03-24T21:57:56Z

On Tue, Mar 24, 2009 at 10:48:46PM +0100, Ingo Molnar wrote:
>
> * Frederic Weisbecker <fweisbec@gmail.com> wrote:
>
> > Well it's a very naive listing, there are sometimes some problems.
> > For example on x86-64, I had to save even some non-scratch
> > registers before calling the return hook, I still don't know why.
>
> btw., which are those registers?
>
> Ingo

I would expect to only save rax,rdi,rsi,rdx,rcx,r8,r9 which
are used for parameters.
And I had some crashes until I append r10 and r11 which actually are
scratch if I'm not wrong, but since they are scratch and are not used for
arguments, I thought they didn't need to be saved.

Well, I think there were some code flow cases I was missing.

The complete code is:

movq %rax, (%rsp)
movq %rcx, 8(%rsp)
movq %rdx, 16(%rsp)
movq %rsi, 24(%rsp)
movq %rdi, 32(%rsp)
movq %r8, 40(%rsp)
movq %r9, 48(%rsp)
movq %r10, 56(%rsp)
movq %r11, 64(%rsp)

call ftrace_return_to_handler

movq %rax, 72(%rsp) <-- get original return value
movq 64(%rsp), %r11
movq 56(%rsp), %r10
movq 48(%rsp), %r9
movq 40(%rsp), %r8
movq 32(%rsp), %rdi
movq 24(%rsp), %rsi
movq 16(%rsp), %rdx
movq 8(%rsp), %rcx
movq (%rsp), %rax
addq $72, %rsp