Excerpts from Christophe Leroy's message of October 18, 2021 5:07 pm:

Le 18/10/2021 à 08:29, Nicholas Piggin a écrit :

quoted

Excerpts from Christophe Leroy's message of October 17, 2021 10:38 pm:

quoted

We have three architectures using function descriptors, each with its
own type and name.

Add a common typedef that can be used in generic code.

Also add a stub typedef for architecture without function descriptors,
to avoid a forest of #ifdefs.

It replaces the similar 'func_desc_t' previously defined in
arch/powerpc/kernel/module_64.c

Reviewed-by: Kees Cook <redacted>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Christophe Leroy <redacted>
---

[...]

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diff --git a/include/asm-generic/sections.h b/include/asm-generic/sections.h
index a918388d9bf6..33b51efe3a24 100644
--- a/include/asm-generic/sections.h
+++ b/include/asm-generic/sections.h

@@ -63,6 +63,9 @@ extern __visible const void __nosave_begin, __nosave_end;
  #else
  #define dereference_function_descriptor(p) ((void *)(p))
  #define dereference_kernel_function_descriptor(p) ((void *)(p))
+typedef struct {
+	unsigned long addr;
+} func_desc_t;
  #endif
  

I think that deserves a comment. If it's just to allow ifdef to be
avoided, I guess that's okay with a comment. Would be nice if you could
cause it to generate a link time error if it was ever used like
undefined functions, but I guess you can't. It's not a necessity though.

I tried to explain it in the commit message, but I can add a comment 
here in addition for sure.

Thanks.

By the way, it IS used in powerpc's module_64.c:

Ah yes of course. I guess the point is function descriptors don't exist 
so it should not be used (in general). powerpc module code knows what it
is doing, I guess it's okay for it to use it.

Thanks,
Nick