On Thu, 11 Feb 2021 13:48:48 -0800
Jason Gerecke <killert...@gmail.com> wrote:
> When compiling an external kernel module with `-O0` or `-O1`, the following
> compile error may be reported:
>
> ./arch/x86/include/asm/jump_label.h:25:2: error: impossible constraint in
> ‘asm’
> 25 | asm_volatile_goto("1:"
> | ^~~~~~~~~~~~~~~~~
>
> It appears that these lower optimization levels prevent GCC from detecting
> that the key/branch arguments can be treated as constants and used as
> immediate operands. To work around this, explicitly add the `const` label.
Yes this makes sense. The "i" constraint needs to be a constant.
Reviewed-by: Steven Rostedt (VMware) <rost...@goodmis.org>
-- Steve
>
> Signed-off-by: Jason Gerecke <jason.gere...@wacom.com>
> Cc: Steven Rostedt <rost...@goodmis.org>
> Cc: Ard Biesheuvel <a...@kernel.org>
> ---
> Marked RFC since I'm not familiar with this subsystem or the asm blocks that
> are impacted. Extra-close inspection would be appreciated.
>
> arch/x86/include/asm/jump_label.h | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/include/asm/jump_label.h
> b/arch/x86/include/asm/jump_label.h
> index 06c3cc22a058..7f2006645d84 100644
> --- a/arch/x86/include/asm/jump_label.h
> +++ b/arch/x86/include/asm/jump_label.h
> @@ -20,7 +20,7 @@
> #include <linux/stringify.h>
> #include <linux/types.h>
>
> -static __always_inline bool arch_static_branch(struct static_key *key, bool
> branch)
> +static __always_inline bool arch_static_branch(struct static_key * const
> key, const bool branch)
> {
> asm_volatile_goto("1:"
> ".byte " __stringify(STATIC_KEY_INIT_NOP) "\n\t"
> @@ -36,7 +36,7 @@ static __always_inline bool arch_static_branch(struct
> static_key *key, bool bran
> return true;
> }
>
> -static __always_inline bool arch_static_branch_jump(struct static_key *key,
> bool branch)
> +static __always_inline bool arch_static_branch_jump(struct static_key *
> const key, const bool branch)
> {
> asm_volatile_goto("1:"
> ".byte 0xe9\n\t .long %l[l_yes] - 2f\n\t"
