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SubjectRe: [PATCH] RFC: x86/jump_label: Mark arguments as const to satisfy asm constraints
On Fri, Feb 12, 2021 at 09:40:59AM -0500, Steven Rostedt wrote:
> On Thu, 11 Feb 2021 13:48:48 -0800
> Jason Gerecke <killertofu@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.

Right, using -O[01] seems a little daft though. But yeah, that patch is
correct and won't cause harm.

I've queued it for after the next merge window.

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