Messages in this thread | | | Date | Wed, 6 Oct 2021 06:54:17 -0700 | From | Josh Poimboeuf <> | Subject | Re: [PATCH v4 06/15] ftrace: Use an opaque type for functions not callable from C |
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On Wed, Oct 06, 2021 at 09:02:49AM -0400, Steven Rostedt wrote: > On Tue, 5 Oct 2021 20:29:45 -0700 > Josh Poimboeuf <jpoimboe@redhat.com> wrote: > > Thanks for Cc'ing me, as I should have been Cc'd on the original patch. > > > 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. > > > > > > > Signed-off-by: Sami Tolvanen <samitolvanen@google.com> > > > --- > > > include/linux/ftrace.h | 7 ++++--- > > > 1 file changed, 4 insertions(+), 3 deletions(-) > > > > > > diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h > > > index 832e65f06754..67de28464aeb 100644 > > > --- a/include/linux/ftrace.h > > > +++ b/include/linux/ftrace.h > > > @@ -578,9 +578,10 @@ extern void ftrace_replace_code(int enable); > > > extern int ftrace_update_ftrace_func(ftrace_func_t func); > > > extern void ftrace_caller(void); > > > extern void ftrace_regs_caller(void); > > > -extern void ftrace_call(void); > > > -extern void ftrace_regs_call(void); > > > -extern void mcount_call(void); > > > + > > > +DECLARE_ASM_FUNC_SYMBOL(ftrace_call); > > > +DECLARE_ASM_FUNC_SYMBOL(ftrace_regs_call); > > > +DECLARE_ASM_FUNC_SYMBOL(mcount_call); > > > > I'm thinking DECLARE_ASM_FUNC_SYMBOL needs a better name. It's not clear > > from reading it why some asm symbols need the macro and others don't. > > > > I guess it means "an asm text symbol which isn't callable from C code > > (not including alternatives)"? > > > > DECLARE_UNCALLED_SYMBOL() maybe? > > > > That's even worse ;-) Because "called" is an assembler command in x86, and > it is "called" from assembly (when you look at an objdump, it is most > definitely "called"). > > Perhaps DECLARE_ASM_INTERNAL_SYMBOL() ? > > Or call it "DECLARE_ASM_MCOUNT_SYMBOL()" as "mcount" is the original name > of what a compiler does when passed the -pg option, and that's exactly what > those functions are.
But this macro is used in other places as well:
https://lkml.kernel.org/r/20210930180531.1190642-10-samitolvanen@google.com
And many of them aren't internal to a function like the above symbols, they're actual functions that are called in other ways.
DECLARE_UNCALLED_FROM_C() ?
-- Josh
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