Commit 864b4355 authored Feb 11, 2021 by Jason Gerecke Committed by Ingo Molnar Mar 06, 2021

x86/jump_label: Mark arguments as const to satisfy asm constraints



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.

Signed-off-by: Jason Gerecke <jason.gerecke@wacom.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lkml.kernel.org/r/20210211214848.536626-1-jason.gerecke@wacom.com

parent a5aabace

arch/x86/include/asm/jump_label.h

+2 −2

Original line number	Diff line number	Diff line
		@@ -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"