linux-kernel - Re: [PATCH] s390/jump_label: Correct asm contraint

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Date:   Tue, 29 Jan 2019 08:25:58 +0100
From:   Laura Abbott <labbott@...hat.com>
To:     Heiko Carstens <heiko.carstens@...ibm.com>,
        Andreas Krebbel <krebbel@...ux.ibm.com>,
        Ilya Leoshkevich <iii@...ux.ibm.com>
Cc:     Martin Schwidefsky <schwidefsky@...ibm.com>,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] s390/jump_label: Correct asm contraint

On 1/23/19 5:24 AM, Heiko Carstens wrote:
> On Wed, Jan 23, 2019 at 01:55:13PM +0100, Laura Abbott wrote:
>> There's a build failure with gcc9:
>>
>>   ./arch/s390/include/asm/jump_label.h: Assembler messages:
>>   ./arch/s390/include/asm/jump_label.h:23: Error: bad expression
>>   ./arch/s390/include/asm/jump_label.h:23: Error: junk at end of line, first unrecognized character is `r'
>>   make[1]: *** [scripts/Makefile.build:277: init/main.o] Error 1
>>
>> According to the toolchain people, the actual issue is the use of
>> "X" constraint which is too permissive. Switch to using "i" instead.
>>
>> Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1668703
>> Signed-off-by: Laura Abbott <labbott@...hat.com>
>> ---
>>   arch/s390/include/asm/jump_label.h | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/s390/include/asm/jump_label.h b/arch/s390/include/asm/jump_label.h
>> index e2d3e6c43395..41dabfd8518d 100644
>> --- a/arch/s390/include/asm/jump_label.h
>> +++ b/arch/s390/include/asm/jump_label.h
>> @@ -22,7 +22,7 @@ static inline bool arch_static_branch(struct static_key *key, bool branch)
>>   			  ".long	0b-.,%l[label]-.\n"
>>   			  ".quad	%0-.\n"
>>   			  ".popsection\n"
>> -			  : : "X" (&((char *)key)[branch]) : : label);
>> +			  : : "i" (&((char *)key)[branch]) : : label);
>>   	return false;
>>   label:
>>   	return true;
> 
> Hmmm, this works only for the kernel image, but not for modules, which
> we compile with "-fPIC", which again doesn't work as described in the
> referenced bugzilla:
> 
> In file included from ././include/linux/compiler_types.h:68,
>                   from <command-line>:
> ./arch/s390/include/asm/jump_label.h: In function 'kvm_vcpu_ioctl':
> ./include/linux/compiler-gcc.h:124:38: warning: asm operand 0 probably doesn't match constraints
>   #define asm_volatile_goto(x...) do { asm goto(x); asm (""); } while (0)
>                                        ^~~
> ./arch/s390/include/asm/jump_label.h:19:2: note: in expansion of macro 'asm_volatile_goto'
>    asm_volatile_goto("0: brcl 0,"__stringify(JUMP_LABEL_NOP_OFFSET)"\n"
>    ^~~~~~~~~~~~~~~~~
> ./include/linux/compiler-gcc.h:124:38: error: impossible constraint in 'asm'
>   #define asm_volatile_goto(x...) do { asm goto(x); asm (""); } while (0)
>                                        ^~~
> ./arch/s390/include/asm/jump_label.h:19:2: note: in expansion of macro 'asm_volatile_goto'
>    asm_volatile_goto("0: brcl 0,"__stringify(JUMP_LABEL_NOP_OFFSET)"\n"
> 
> Andreas, Ilya, any idea how to fix this?
> 

I've had to turn off s390 in Fedora until this gets fixed :(