* Re: [PATCH] RFC: x86/jump_label: Mark arguments as const to satisfy asm constraints
2021-02-11 21:48 [PATCH] RFC: x86/jump_label: Mark arguments as const to satisfy asm constraints Jason Gerecke
@ 2021-02-12 14:40 ` Steven Rostedt
2021-02-12 15:27 ` Peter Zijlstra
2021-02-12 16:14 ` Josh Poimboeuf
` (2 subsequent siblings)
3 siblings, 1 reply; 7+ messages in thread
From: Steven Rostedt @ 2021-02-12 14:40 UTC (permalink / raw)
To: Jason Gerecke
Cc: linux-kernel, Peter Zijlstra, Josh Poimboeuf, Jason Baron,
Jason Gerecke, Ard Biesheuvel, x86
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.
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
-- Steve
>
> 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"
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] RFC: x86/jump_label: Mark arguments as const to satisfy asm constraints
2021-02-12 14:40 ` Steven Rostedt
@ 2021-02-12 15:27 ` Peter Zijlstra
2021-02-12 15:55 ` Jason Gerecke
0 siblings, 1 reply; 7+ messages in thread
From: Peter Zijlstra @ 2021-02-12 15:27 UTC (permalink / raw)
To: Steven Rostedt
Cc: Jason Gerecke, linux-kernel, Josh Poimboeuf, Jason Baron,
Jason Gerecke, Ard Biesheuvel, x86
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.
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] RFC: x86/jump_label: Mark arguments as const to satisfy asm constraints
2021-02-12 15:27 ` Peter Zijlstra
@ 2021-02-12 15:55 ` Jason Gerecke
0 siblings, 0 replies; 7+ messages in thread
From: Jason Gerecke @ 2021-02-12 15:55 UTC (permalink / raw)
To: Peter Zijlstra
Cc: Steven Rostedt, LKML, Josh Poimboeuf, Jason Baron, Jason Gerecke,
Ard Biesheuvel, x86
On Fri, Feb 12, 2021 at 7:27 AM Peter Zijlstra <peterz@infradead.org> wrote:
>
> 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.
Thanks. Only reason I even tried compiling at those levels was to play
around with GCC's new static analyzer options. They seem to be
ineffective at more normal optimization levels.
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] RFC: x86/jump_label: Mark arguments as const to satisfy asm constraints
2021-02-11 21:48 [PATCH] RFC: x86/jump_label: Mark arguments as const to satisfy asm constraints Jason Gerecke
2021-02-12 14:40 ` Steven Rostedt
@ 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
3 siblings, 0 replies; 7+ messages in thread
From: Josh Poimboeuf @ 2021-02-12 16:14 UTC (permalink / raw)
To: Jason Gerecke
Cc: linux-kernel, Peter Zijlstra, Jason Baron, Jason Gerecke,
Steven Rostedt, Ard Biesheuvel
On Thu, Feb 11, 2021 at 01:48:48PM -0800, Jason Gerecke 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.
>
> 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.
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
--
Josh
^ permalink raw reply [flat|nested] 7+ messages in thread
* [tip: locking/core] x86/jump_label: Mark arguments as const to satisfy asm constraints
2021-02-11 21:48 [PATCH] RFC: x86/jump_label: Mark arguments as const to satisfy asm constraints Jason Gerecke
2021-02-12 14:40 ` Steven Rostedt
2021-02-12 16:14 ` Josh Poimboeuf
@ 2021-03-03 8:15 ` tip-bot2 for Jason Gerecke
2021-03-06 11:54 ` tip-bot2 for Jason Gerecke
3 siblings, 0 replies; 7+ messages in thread
From: tip-bot2 for Jason Gerecke @ 2021-03-03 8:15 UTC (permalink / raw)
To: linux-tip-commits
Cc: Jason Gerecke, Peter Zijlstra (Intel), Steven Rostedt (VMware),
Josh Poimboeuf, x86, linux-kernel
The following commit has been merged into the locking/core branch of tip:
Commit-ID: 566a9522381495d27b596ee3bdc9578ba02a895d
Gitweb: https://git.kernel.org/tip/566a9522381495d27b596ee3bdc9578ba02a895d
Author: Jason Gerecke <killertofu@gmail.com>
AuthorDate: Thu, 11 Feb 2021 13:48:48 -08:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Tue, 02 Mar 2021 15:06:34 +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@wacom.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.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
---
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"
^ permalink raw reply related [flat|nested] 7+ messages in thread
* [tip: locking/core] x86/jump_label: Mark arguments as const to satisfy asm constraints
2021-02-11 21:48 [PATCH] RFC: x86/jump_label: Mark arguments as const to satisfy asm constraints Jason Gerecke
` (2 preceding siblings ...)
2021-03-03 8:15 ` [tip: locking/core] " tip-bot2 for Jason Gerecke
@ 2021-03-06 11:54 ` tip-bot2 for Jason Gerecke
3 siblings, 0 replies; 7+ messages in thread
From: tip-bot2 for Jason Gerecke @ 2021-03-06 11:54 UTC (permalink / raw)
To: linux-tip-commits
Cc: Jason Gerecke, Peter Zijlstra (Intel),
Ingo Molnar, Steven Rostedt (VMware),
Josh Poimboeuf, x86, linux-kernel
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@gmail.com>
AuthorDate: Thu, 11 Feb 2021 13:48:48 -08:00
Committer: Ingo Molnar <mingo@kernel.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@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
---
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"
^ permalink raw reply related [flat|nested] 7+ messages in thread