linux-kernel - [tip: locking/core] x86/jump_label: Mark arguments as const to satisfy asm constraints

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Date:   Sat, 06 Mar 2021 11:54:34 -0000
From:   "tip-bot2 for Jason Gerecke" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Jason Gerecke <jason.gerecke@...om.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: locking/core] x86/jump_label: Mark arguments as const to
 satisfy asm constraints

The following commit has been merged into the locking/core branch of tip:

Commit-ID:     864b435514b286c0be2a38a02f487aa28d990ef8
Gitweb:        https://git.kernel.org/tip/864b435514b286c0be2a38a02f487aa28d990ef8
Author:        Jason Gerecke <killertofu@...il.com>
AuthorDate:    Thu, 11 Feb 2021 13:48:48 -08:00
Committer:     Ingo Molnar <mingo@...nel.org>
CommitterDate: Sat, 06 Mar 2021 12:51:00 +01:00

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@...om.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Reviewed-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
Acked-by: Josh Poimboeuf <jpoimboe@...hat.com>
Link: https://lkml.kernel.org/r/20210211214848.536626-1-jason.gerecke@wacom.com
---
 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 06c3cc2..7f20066 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 @@ l_yes:
 	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"