Re: [PATCH v4 06/15] ftrace: Use an opaque type for functions not callable from C

Josh Poimboeuf
2021-10-06T21:24:04Z

On Wed, Oct 06, 2021 at 05:10:16PM -0400, Steven Rostedt wrote:
> On Wed, 6 Oct 2021 13:43:35 -0700
> Josh Poimboeuf <jpoimboe@redhat.com> wrote:
>
> > On Wed, Oct 06, 2021 at 10:45:41AM -0700, Sami Tolvanen wrote:
> > > On Wed, Oct 6, 2021 at 9:58 AM Steven Rostedt <rostedt@goodmis.org> wrote:
> > > >
> > > > On Wed, 6 Oct 2021 09:31:04 -0700
> > > > Sami Tolvanen <samitolvanen@google.com> wrote:
> > > >
> > > > > > > On Thu, Sep 30, 2021 at 11:05:22AM -0700, Sami Tolvanen wrote:
> > > > > > > > With CONFIG_CFI_CLANG, the compiler changes function references to point
> > > > > > > > to the CFI jump table. As ftrace_call, ftrace_regs_call, and mcount_call
> > > > > > > > are not called from C, use DECLARE_ASM_FUNC_SYMBOL to declare them.
> > > > > >
> > > > > > "not called from C" is a bit confusing.
> > > > >
> > > > > Any thoughts on how to make this less confusing?
> > > >
> > > > "Not called by C code, but injected by the compiler."
> > > >
> > > > ?
> > >
> > > Sure, sounds good to me. I'll update this in v5.
> >
> > "injected by the compiler" sounds even more confusing. It almost sounds
> > like those functions are generated by GCC, which they are most
> > definitely not.
> >
>
> Heh, I was thinking of the locations that are injected (mcount / fentry) as
> these are just replacements for them. Those injections are added by GCC.
>
> So, continuing the bikeshedding, what about "not called by C code, but are
> trampolines injected as calls replacing the nops at the start of
> functions added by the compiler." ?

I'm not quite sure what that means, but I'll allow it ;-)

--
Josh