2009-11-02 00:51:52

by Li Zefan

Subject: [PATCH 1/2] compiler: Introduce __always_unused

I wrote some code which is used as compile-time checker, and the
code should be elided after compile.

So I need to annotate the code as "always unused", compared to
"maybe unused".

Signed-off-by: Li Zefan <[email protected]>
---
include/linux/compiler-gcc.h | 1 +
include/linux/compiler.h | 4 ++++
2 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
index a3ed7cb..73dcf80 100644
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -79,6 +79,7 @@
#define noinline __attribute__((noinline))
#define __attribute_const__ __attribute__((__const__))
#define __maybe_unused __attribute__((unused))
+#define __always_unused __attribute__((unused))

#define __gcc_header(x) #x
#define _gcc_header(x) __gcc_header(linux/compiler-gcc##x.h)
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index d1cc9f0..1ccebf4 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -132,6 +132,10 @@ extern void __chk_io_ptr(const volatile void __iomem *);
# define __maybe_unused /* unimplemented */
#endif

+#ifndef __always_unused
+# define __always_unused /* unimplemented */
+#endif
+
#ifndef noinline
#define noinline
#endif
--
1.6.3

2009-11-02 00:52:09

by Li Zefan

Subject: [PATCH 2/2] tracing: Fix to use __always_unused attribute

____ftrace_check_##name() is used for compile-time check on
F_printk() only, so it should be marked as __unused instead
of __used.

Signed-off-by: Li Zefan <[email protected]>
---
kernel/trace/trace_export.c | 4 ++--
1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace_export.c b/kernel/trace/trace_export.c
index 934d81f..dff8c84 100644
--- a/kernel/trace/trace_export.c
+++ b/kernel/trace/trace_export.c
@@ -48,11 +48,11 @@
struct ____ftrace_##name { \
tstruct \
}; \
-static void __used ____ftrace_check_##name(void) \
+static void __always_unused ____ftrace_check_##name(void) \
{ \
struct ____ftrace_##name *__entry = NULL; \
\
- /* force cmpile-time check on F_printk() */ \
+ /* force compile-time check on F_printk() */ \
printk(print); \
}

--
1.6.3

2009-11-02 01:14:33

by Arjan van de Ven

Subject: Re: [PATCH 1/2] compiler: Introduce __always_unused

On Mon, 02 Nov 2009 08:50:52 +0800
Li Zefan <[email protected]> wrote:

Hi,

> I wrote some code which is used as compile-time checker, and the
> code should be elided after compile.
> +#define __always_unused
> __attribute__((unused))

I have a suggestion.
In addition to marking it attribute unused, would it be useful to also
put a section attribute as part of this, to a section that we can then
drop from the binary by way of the linker script ?



--
Arjan van de Ven Intel Open Source Technology Centre
For development, discussion and tips for power savings,
visit http://www.lesswatts.org

2009-11-02 02:05:43

by Li Zefan

Subject: Re: [PATCH 1/2] compiler: Introduce __always_unused

Arjan van de Ven wrote:
> On Mon, 02 Nov 2009 08:50:52 +0800
> Li Zefan <[email protected]> wrote:
>
> Hi,
>
>> I wrote some code which is used as compile-time checker, and the
>> code should be elided after compile.
>> +#define __always_unused
>> __attribute__((unused))
>
> I have a suggestion.
> In addition to marking it attribute unused, would it be useful to also
> put a section attribute as part of this, to a section that we can then
> drop from the binary by way of the linker script ?
>

__unused is used to suppress define-but-unused warning. If the
annotated symbol is really unused, it will be optimized out,
so I think we don't need to add a section for this.

2009-11-02 16:17:02

by Li Zefan

Subject: [tip:tracing/core] compiler: Introduce __always_unused

Commit-ID: 7b2a35132ad0a70902dcd2844c27ed64cda0ce9b
Gitweb: http://git.kernel.org/tip/7b2a35132ad0a70902dcd2844c27ed64cda0ce9b
Author: Li Zefan <[email protected]>
AuthorDate: Mon, 2 Nov 2009 08:50:52 +0800
Committer: Ingo Molnar <[email protected]>
CommitDate: Mon, 2 Nov 2009 15:47:54 +0100

compiler: Introduce __always_unused

I wrote some code which is used as compile-time checker, and the
code should be elided after compile.

So I need to annotate the code as "always unused", compared to
"maybe unused".

Signed-off-by: Li Zefan <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Cc: Linus Torvalds <[email protected]>
LKML-Reference: <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
---
include/linux/compiler-gcc.h | 1 +
include/linux/compiler.h | 4 ++++
2 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
index a3ed7cb..73dcf80 100644
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -79,6 +79,7 @@
#define noinline __attribute__((noinline))
#define __attribute_const__ __attribute__((__const__))
#define __maybe_unused __attribute__((unused))
+#define __always_unused __attribute__((unused))

#define __gcc_header(x) #x
#define _gcc_header(x) __gcc_header(linux/compiler-gcc##x.h)
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 04fb513..7947f4f 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -213,6 +213,10 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect);
# define __maybe_unused /* unimplemented */
#endif

+#ifndef __always_unused
+# define __always_unused /* unimplemented */
+#endif
+
#ifndef noinline
#define noinline
#endif

2009-11-02 16:17:33

by Li Zefan

Subject: [tip:tracing/core] tracing: Fix to use __always_unused attribute

Commit-ID: 5e9b397292ca0b9409dced33e3a22ec993377064
Gitweb: http://git.kernel.org/tip/5e9b397292ca0b9409dced33e3a22ec993377064
Author: Li Zefan <[email protected]>
AuthorDate: Mon, 2 Nov 2009 08:51:13 +0800
Committer: Ingo Molnar <[email protected]>
CommitDate: Mon, 2 Nov 2009 15:47:54 +0100

tracing: Fix to use __always_unused attribute

____ftrace_check_##name() is used for compile-time check on
F_printk() only, so it should be marked as __unused instead
of __used.

Signed-off-by: Li Zefan <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Cc: Linus Torvalds <[email protected]>
LKML-Reference: <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
---
kernel/trace/trace_export.c | 4 ++--
1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace_export.c b/kernel/trace/trace_export.c
index 9753fcc..c74848d 100644
--- a/kernel/trace/trace_export.c
+++ b/kernel/trace/trace_export.c
@@ -48,11 +48,11 @@
struct ____ftrace_##name { \
tstruct \
}; \
-static void __used ____ftrace_check_##name(void) \
+static void __always_unused ____ftrace_check_##name(void) \
{ \
struct ____ftrace_##name *__entry = NULL; \
\
- /* force cmpile-time check on F_printk() */ \
+ /* force compile-time check on F_printk() */ \
printk(print); \
}