lkml.org 
[lkml]   [2022]   [May]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v2] ftrace: Add FTRACE_MCOUNT_MAX_OFFSET to avoid adding weak function
On Thu, 26 May 2022 09:39:49 +0200
Peter Zijlstra <peterz@infradead.org> wrote:

> > If CONFIG_HAVE_FENTRY is defined for x86, define FTRACE_MCOUNT_MAX_OFFSET
> > to zero, which will have ftrace ignore all locations that are not at the
> > start of the function.
>
> ^^^ that paragraph is obsolete by your own changes thing below :-)

Well, it is partially correct (if X86_KERNEL_IBT is disabled).

I'll update the change log to reflect the update.

>
> > [1] https://lore.kernel.org/all/20220412094923.0abe90955e5db486b7bca279@kernel.org/
> >
> > Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
> > ---
> > Changes since v1: https://lore.kernel.org/all/20220503150410.2d9e88aa@rorschach.local.home/
> >
> > - Changed MAX_OFFSET to 4 on x86 if KERNEL_IBT is enabled
> > (Reminded by Peter Zijlstra)
> >
> > arch/x86/include/asm/ftrace.h | 10 +++++++
> > kernel/trace/ftrace.c | 50 +++++++++++++++++++++++++++++++++--
> > 2 files changed, 58 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/x86/include/asm/ftrace.h b/arch/x86/include/asm/ftrace.h
> > index 024d9797646e..53675fe2d847 100644
> > --- a/arch/x86/include/asm/ftrace.h
> > +++ b/arch/x86/include/asm/ftrace.h
> > @@ -9,6 +9,16 @@
> > # define MCOUNT_ADDR ((unsigned long)(__fentry__))
> > #define MCOUNT_INSN_SIZE 5 /* sizeof mcount call */
> >
> > +/* Ignore unused weak functions which will have non zero offsets */
> > +#ifdef CONFIG_HAVE_FENTRY
> > +# ifdef CONFIG_X86_KERNEL_IBT
> > +/* endbr64 is 4 bytes in front of the fentry */
> > +# define FTRACE_MCOUNT_MAX_OFFSET 4
> > +# else
> > +# define FTRACE_MCOUNT_MAX_OFFSET 0
> > +# endif
> > +#endif
>
> #define FTRACE_MCOUNT_MAX_OFFSET ENDBR_INSN_SIZE
>
> Should do the same I think, less lines etc..

Thanks, I figured there was something else I could use besides hard coding
it. But I may add that as a separate patch after this gets merged, because
my branch doesn't have that code in it yet, so it wont compile.

-- Steve

\
 
 \ /
  Last update: 2022-05-26 15:16    [W:0.075 / U:0.048 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site