Re: [PATCH] [Rebased for 5.15,5.16,5.17] static_call: Don't make __static_call_return0 static

[Greg KH <gregkh@linuxfoundation.org>]

On Mon, Apr 11, 2022 at 06:54:43PM +0200, Christophe Leroy wrote:
> This is backport to 5.15,5.16,5.17
> 
> (cherry picked from commit 8fd4ddda2f49a66bf5dd3d0c01966c4b1971308b)
> 
> System.map shows that vmlinux contains several instances of
> __static_call_return0():
> 
> 	c0004fc0 t __static_call_return0
> 	c0011518 t __static_call_return0
> 	c00d8160 t __static_call_return0
> 
> arch_static_call_transform() uses the middle one to check whether we are
> setting a call to __static_call_return0 or not:
> 
> 	c0011520 <arch_static_call_transform>:
> 	c0011520:       3d 20 c0 01     lis     r9,-16383	<== r9 =  0xc001 << 16
> 	c0011524:       39 29 15 18     addi    r9,r9,5400	<== r9 += 0x1518
> 	c0011528:       7c 05 48 00     cmpw    r5,r9		<== r9 has value 0xc0011518 here
> 
> So if static_call_update() is called with one of the other instances of
> __static_call_return0(), arch_static_call_transform() won't recognise it.
> 
> In order to work properly, global single instance of __static_call_return0() is required.
> 
> Fixes: 3f2a8fc4b15d ("static_call/x86: Add __static_call_return0()")
> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
> Link: https://lkml.kernel.org/r/30821468a0e7d28251954b578e5051dc09300d04.1647258493.git.christophe.leroy@csgroup.eu
> ---
>  include/linux/static_call.h                   |   5 +-
>  kernel/Makefile                               |   3 +-
>  kernel/static_call.c                          | 542 +-----------------
>  .../{static_call.c => static_call_inline.c}   |   5 -
>  4 files changed, 4 insertions(+), 551 deletions(-)
>  copy kernel/{static_call.c => static_call_inline.c} (99%)

Thanks for this, now queued up!

greg k-h