On Wed, Oct 06, 2021 at 09:02:49AM -0400, Steven Rostedt wrote:

On Tue, 5 Oct 2021 20:29:45 -0700
Josh Poimboeuf [off-list ref] wrote:

Thanks for Cc'ing me, as I should have been Cc'd on the original patch.

quoted

On Thu, Sep 30, 2021 at 11:05:22AM -0700, Sami Tolvanen wrote:

quoted

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.

quoted

quoted

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