Re: [RFC][PATCH] ftrace/x86: Remove mcount support

[Steven Rostedt]

On Thu, 9 May 2019 15:14:30 -0500
Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote:

> > Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
> > ---
> >  arch/x86/include/asm/ftrace.h    |  8 +++----
> >  arch/x86/include/asm/livepatch.h |  3 ---
> >  arch/x86/kernel/ftrace_32.S      | 36 +++++---------------------------
> >  arch/x86/kernel/ftrace_64.S      | 28 +------------------------
> >  4 files changed, 9 insertions(+), 66 deletions(-)  
> 
> I was wondering why you didn't do s/mcount/fentry/ everywhere, but I
> guess it's because mcount is still used by other arches, so it still has
> a generic meaning tree-wide, right?

Yes, fentry works nicely when you have a single instruction that pushes
the return address on the stack and then jumps to another location.
It's much trickier to implement with link registers. There's a few
different implementations for other archs, but mcount happens to be the
one supported by most.

> 
> Anyway it's nice to finally see this cruft disappear.
> 
> Acked-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>

Thanks!

-- Steve