From: Jason Gerecke <killertofu@gmail.com>
To: linux-kernel@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>,
Josh Poimboeuf <jpoimboe@redhat.com>,
Jason Baron <jbaron@akamai.com>
Cc: Jason Gerecke <jason.gerecke@wacom.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ard Biesheuvel <ardb@kernel.org>
Subject: [PATCH] RFC: x86/jump_label: Mark arguments as const to satisfy asm constraints
Date: Thu, 11 Feb 2021 13:48:48 -0800 [thread overview]
Message-ID: <20210211214848.536626-1-jason.gerecke@wacom.com> (raw)
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>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ard Biesheuvel <ardb@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"
--
2.30.1
next reply other threads:[~2021-02-11 21:49 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-11 21:48 Jason Gerecke [this message]
2021-02-12 14:40 ` [PATCH] RFC: x86/jump_label: Mark arguments as const to satisfy asm constraints Steven Rostedt
2021-02-12 15:27 ` Peter Zijlstra
2021-02-12 15:55 ` Jason Gerecke
2021-02-12 16:14 ` Josh Poimboeuf
2021-03-03 8:15 ` [tip: locking/core] " tip-bot2 for Jason Gerecke
2021-03-06 11:54 ` tip-bot2 for Jason Gerecke
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