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

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Date:   Wed, 6 Oct 2021 13:43:35 -0700
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Sami Tolvanen <samitolvanen@...gle.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>, X86 ML <x86@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Sedat Dilek <sedat.dilek@...il.com>,
        linux-hardening@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>, llvm@...ts.linux.dev
Subject: Re: [PATCH v4 06/15] ftrace: Use an opaque type for functions not
 callable from C

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@...dmis.org> wrote:
> >
> > On Wed, 6 Oct 2021 09:31:04 -0700
> > Sami Tolvanen <samitolvanen@...gle.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.

-- 
Josh