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SubjectRe: [PATCH] s390/jump_label: Correct asm contraint
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@redhat.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?

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