From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

In order to be able to use ftrace_regs even from features unrelated to
function tracer (e.g. kretprobe), expose ftrace_regs structures and
APIs even if the CONFIG_FUNCTION_TRACER=n.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
 include/linux/ftrace.h |   45 ++++++++++++++++++++++++---------------------
 1 file changed, 24 insertions(+), 21 deletions(-)

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index ce156c7704ee..3fb94a1a2461 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -112,11 +112,11 @@ static inline int ftrace_mod_get_kallsym(unsigned int symnum, unsigned long *val
 }
 #endif
 
-#ifdef CONFIG_FUNCTION_TRACER
-
-extern int ftrace_enabled;
-
-#ifndef CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS
+/*
+ * If the architecture doesn't support FTRACE_WITH_ARGS or disable function
+ * tracer, define the default(pt_regs compatible) ftrace_regs.
+ */
+#if !defined(CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS) || !defined(CONFIG_FUNCTION_TRACER)
 
 struct ftrace_regs {
 	struct pt_regs		regs;
@@ -129,6 +129,22 @@ struct ftrace_regs {
  * HAVE_DYNAMIC_FTRACE_WITH_ARGS is set and it supports live kernel patching.
  */
 #define ftrace_regs_set_instruction_pointer(fregs, ip) do { } while (0)
+
+#define ftrace_regs_get_instruction_pointer(fregs) \
+	instruction_pointer(ftrace_get_regs(fregs))
+#define ftrace_regs_get_argument(fregs, n) \
+	regs_get_kernel_argument(ftrace_get_regs(fregs), n)
+#define ftrace_regs_get_stack_pointer(fregs) \
+	kernel_stack_pointer(ftrace_get_regs(fregs))
+#define ftrace_regs_return_value(fregs) \
+	regs_return_value(ftrace_get_regs(fregs))
+#define ftrace_regs_set_return_value(fregs, ret) \
+	regs_set_return_value(ftrace_get_regs(fregs), ret)
+#define ftrace_override_function_with_return(fregs) \
+	override_function_with_return(ftrace_get_regs(fregs))
+#define ftrace_regs_query_register_offset(name) \
+	regs_query_register_offset(name)
+
 #endif /* CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS */
 
 static __always_inline struct pt_regs *ftrace_get_regs(struct ftrace_regs *fregs)
@@ -151,22 +167,9 @@ static __always_inline bool ftrace_regs_has_args(struct ftrace_regs *fregs)
 	return ftrace_get_regs(fregs) != NULL;
 }
 
-#ifndef CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS
-#define ftrace_regs_get_instruction_pointer(fregs) \
-	instruction_pointer(ftrace_get_regs(fregs))
-#define ftrace_regs_get_argument(fregs, n) \
-	regs_get_kernel_argument(ftrace_get_regs(fregs), n)
-#define ftrace_regs_get_stack_pointer(fregs) \
-	kernel_stack_pointer(ftrace_get_regs(fregs))
-#define ftrace_regs_return_value(fregs) \
-	regs_return_value(ftrace_get_regs(fregs))
-#define ftrace_regs_set_return_value(fregs, ret) \
-	regs_set_return_value(ftrace_get_regs(fregs), ret)
-#define ftrace_override_function_with_return(fregs) \
-	override_function_with_return(ftrace_get_regs(fregs))
-#define ftrace_regs_query_register_offset(name) \
-	regs_query_register_offset(name)
-#endif
+#ifdef CONFIG_FUNCTION_TRACER
+
+extern int ftrace_enabled;
 
 typedef void (*ftrace_func_t)(unsigned long ip, unsigned long parent_ip,
 			      struct ftrace_ops *op, struct ftrace_regs *fregs);

On Mon, Aug 7, 2023 at 8:48 AM Masami Hiramatsu (Google)
<mhiramat@kernel.org> wrote:
> diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
> index ce156c7704ee..3fb94a1a2461 100644
> --- a/include/linux/ftrace.h
> +++ b/include/linux/ftrace.h
> @@ -112,11 +112,11 @@ static inline int ftrace_mod_get_kallsym(unsigned int symnum, unsigned long *val
>  }
>  #endif
>
> -#ifdef CONFIG_FUNCTION_TRACER
> -
> -extern int ftrace_enabled;
> -
> -#ifndef CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS
> +/*
> + * If the architecture doesn't support FTRACE_WITH_ARGS or disable function

nit: disables*

> + * tracer, define the default(pt_regs compatible) ftrace_regs.
> + */
> +#if !defined(CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS) || !defined(CONFIG_FUNCTION_TRACER)

I wonder if we should make things simpler with:

#if defined(HAVE_PT_REGS_COMPAT_FTRACE_REGS) || !defined(CONFIG_FUNCTION_TRACER)

And remove the ftrace_regs definitions that are copy-pastes of this
block in arch specific headers. Then we can enforce in a single point
that HAVE_PT_REGS_COMPAT_FTRACE_REGS holds.

Maybe that's a question for Steven ?

On Wed, 9 Aug 2023 12:29:13 +0200
Florent Revest <revest@chromium.org> wrote:

> On Mon, Aug 7, 2023 at 8:48 AM Masami Hiramatsu (Google)
> <mhiramat@kernel.org> wrote:
> > diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
> > index ce156c7704ee..3fb94a1a2461 100644
> > --- a/include/linux/ftrace.h
> > +++ b/include/linux/ftrace.h
> > @@ -112,11 +112,11 @@ static inline int ftrace_mod_get_kallsym(unsigned int symnum, unsigned long *val
> >  }
> >  #endif
> >
> > -#ifdef CONFIG_FUNCTION_TRACER
> > -
> > -extern int ftrace_enabled;
> > -
> > -#ifndef CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS
> > +/*
> > + * If the architecture doesn't support FTRACE_WITH_ARGS or disable function
> 
> nit: disables*

Thanks!

> 
> > + * tracer, define the default(pt_regs compatible) ftrace_regs.
> > + */
> > +#if !defined(CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS) || !defined(CONFIG_FUNCTION_TRACER)
> 
> I wonder if we should make things simpler with:
> 
> #if defined(HAVE_PT_REGS_COMPAT_FTRACE_REGS) || !defined(CONFIG_FUNCTION_TRACER)
> 
> And remove the ftrace_regs definitions that are copy-pastes of this
> block in arch specific headers. Then we can enforce in a single point
> that HAVE_PT_REGS_COMPAT_FTRACE_REGS holds.

Here, the "HAVE_PT_REGS_COMPAT_FTRACE_REGS" does not mean that the
ftrace_regs is completely compatible with pt_regs, but on the memory
it wraps struct pt_regs (thus we can just cast the type).

- CONFIG_DYNAMIC_FTRACE_WITH_REGS
  ftrace_regs is completely compatible with pt_regs

- CONFIG_DYNAMIC_FTRACE_WITH_ARGS
  |   ftrace_regs may not compatible with pt_regs
  |
  +- CONFIG_HAVE_PT_REGS_COMPAT_FTRACE_REGS
     but on memory image, ftrace_regs includes pt_regs.

Thank you,

> 
> Maybe that's a question for Steven ?


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>

On Wed, Aug 9, 2023 at 4:16 PM Masami Hiramatsu <mhiramat@kernel.org> wrote:
>
> On Wed, 9 Aug 2023 12:29:13 +0200
> Florent Revest <revest@chromium.org> wrote:
> > > + * tracer, define the default(pt_regs compatible) ftrace_regs.
> > > + */
> > > +#if !defined(CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS) || !defined(CONFIG_FUNCTION_TRACER)
> >
> > I wonder if we should make things simpler with:
> >
> > #if defined(HAVE_PT_REGS_COMPAT_FTRACE_REGS) || !defined(CONFIG_FUNCTION_TRACER)
> >
> > And remove the ftrace_regs definitions that are copy-pastes of this
> > block in arch specific headers. Then we can enforce in a single point
> > that HAVE_PT_REGS_COMPAT_FTRACE_REGS holds.
>
> Here, the "HAVE_PT_REGS_COMPAT_FTRACE_REGS" does not mean that the
> ftrace_regs is completely compatible with pt_regs, but on the memory
> it wraps struct pt_regs (thus we can just cast the type).

But in practice I think that all architectures that chose to wrap a
pt_regs in their ftrace_regs also do:

+#define ftrace_regs_get_instruction_pointer(fregs) \
+       instruction_pointer(ftrace_get_regs(fregs))
+#define ftrace_regs_get_argument(fregs, n) \
+       regs_get_kernel_argument(ftrace_get_regs(fregs), n)
+#define ftrace_regs_get_stack_pointer(fregs) \
+       kernel_stack_pointer(ftrace_get_regs(fregs))
+#define ftrace_regs_return_value(fregs) \
+       regs_return_value(ftrace_get_regs(fregs))
+#define ftrace_regs_set_return_value(fregs, ret) \
+       regs_set_return_value(ftrace_get_regs(fregs), ret)
+#define ftrace_override_function_with_return(fregs) \
+       override_function_with_return(ftrace_get_regs(fregs))
+#define ftrace_regs_query_register_offset(name) \
+       regs_query_register_offset(name)

And are just careful to populate the fields that let these macros
work. So maybe these could be factorized... But anyway, I'm not
particularly a super fan of the idea and I don't think it should
necessarily fit in that series. It's just something that crossed my
mind, if you're not a fan then we should probably not do it ;)