Re: [PATCH] static_call: Don't make __static_call_return0 static

[Christophe Leroy]

Le 15/03/2022 à 22:11, Josh Poimboeuf a écrit :
> On Mon, Mar 14, 2022 at 08:21:30AM +0100, Christophe Leroy wrote:
>> 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@xxxxxxxxxx>
> 
> Acked-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
> 

Thanks for this Ack.

By the way I sent version v2 before your Ack for a missing #include

Christophe