The motivation of commit abb2ea7dfd82 ("compiler, clang: suppress warning
for unused static inline functions") is to suppress clang's warnings about
unused static inline functions.
For configs without CONFIG_OPTIMIZE_INLINING enabled, such as any non-x86
architecture, `inline' in the kernel implies that
__attribute__((always_inline)) is used.
Some code depends on that behavior, see
https://lkml.org/lkml/2017/6/13/918:
net/built-in.o: In function `__xchg_mb':
arch/arm64/include/asm/cmpxchg.h:99: undefined reference to `__compiletime_assert_99'
arch/arm64/include/asm/cmpxchg.h:99: undefined reference to `__compiletime_assert_99
The full fix would be to identify these breakages and annotate the
functions with __always_inline instead of `inline'. But since we are late
in the 4.12-rc cycle, simply carry forward the forced inlining behavior
and work toward moving arm64, and other architectures, toward
CONFIG_OPTIMIZE_INLINING behavior.
Reported-by: Sodagudi Prasad <[email protected]>
Tested-by: Matthias Kaehlcke <[email protected]>
Signed-off-by: David Rientjes <[email protected]>
---
Resend of http://marc.info/?l=linux-kernel&m=149681501816319 for 4.12
inclusion.
Prasad, please add your Tested-by.
include/linux/compiler-clang.h | 8 --------
include/linux/compiler-gcc.h | 18 +++++++++++-------
2 files changed, 11 insertions(+), 15 deletions(-)
diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
--- a/include/linux/compiler-clang.h
+++ b/include/linux/compiler-clang.h
@@ -15,11 +15,3 @@
* with any version that can compile the kernel
*/
#define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __COUNTER__)
-
-/*
- * GCC does not warn about unused static inline functions for
- * -Wunused-function. This turns out to avoid the need for complex #ifdef
- * directives. Suppress the warning in clang as well.
- */
-#undef inline
-#define inline inline __attribute__((unused)) notrace
diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -66,18 +66,22 @@
/*
* Force always-inline if the user requests it so via the .config,
- * or if gcc is too old:
+ * or if gcc is too old.
+ * GCC does not warn about unused static inline functions for
+ * -Wunused-function. This turns out to avoid the need for complex #ifdef
+ * directives. Suppress the warning in clang as well by using "unused"
+ * function attribute, which is redundant but not harmful for gcc.
*/
#if !defined(CONFIG_ARCH_SUPPORTS_OPTIMIZED_INLINING) || \
!defined(CONFIG_OPTIMIZE_INLINING) || (__GNUC__ < 4)
-#define inline inline __attribute__((always_inline)) notrace
-#define __inline__ __inline__ __attribute__((always_inline)) notrace
-#define __inline __inline __attribute__((always_inline)) notrace
+#define inline inline __attribute__((always_inline,unused)) notrace
+#define __inline__ __inline__ __attribute__((always_inline,unused)) notrace
+#define __inline __inline __attribute__((always_inline,unused)) notrace
#else
/* A lot of inline functions can cause havoc with function tracing */
-#define inline inline notrace
-#define __inline__ __inline__ notrace
-#define __inline __inline notrace
+#define inline inline __attribute__((unused)) notrace
+#define __inline__ __inline__ __attribute__((unused)) notrace
+#define __inline __inline __attribute__((unused)) notrace
#endif
#define __always_inline inline __attribute__((always_inline))
On 2017-06-26 16:03, David Rientjes wrote:
> The motivation of commit abb2ea7dfd82 ("compiler, clang: suppress
> warning
> for unused static inline functions") is to suppress clang's warnings
> about
> unused static inline functions.
>
> For configs without CONFIG_OPTIMIZE_INLINING enabled, such as any
> non-x86
> architecture, `inline' in the kernel implies that
> __attribute__((always_inline)) is used.
>
> Some code depends on that behavior, see
> https://lkml.org/lkml/2017/6/13/918:
>
> net/built-in.o: In function `__xchg_mb':
> arch/arm64/include/asm/cmpxchg.h:99: undefined reference to
> `__compiletime_assert_99'
> arch/arm64/include/asm/cmpxchg.h:99: undefined reference to
> `__compiletime_assert_99
>
> The full fix would be to identify these breakages and annotate the
> functions with __always_inline instead of `inline'. But since we are
> late
> in the 4.12-rc cycle, simply carry forward the forced inlining behavior
> and work toward moving arm64, and other architectures, toward
> CONFIG_OPTIMIZE_INLINING behavior.
>
> Reported-by: Sodagudi Prasad <[email protected]>
> Tested-by: Matthias Kaehlcke <[email protected]>
> Signed-off-by: David Rientjes <[email protected]>
> ---
> Resend of http://marc.info/?l=linux-kernel&m=149681501816319 for 4.12
> inclusion.
>
> Prasad, please add your Tested-by.
>
I have compile tested this change with clang, please add -
Tested-by: Sodagudi Prasad <[email protected]>
-Thanks, Prasad
> include/linux/compiler-clang.h | 8 --------
> include/linux/compiler-gcc.h | 18 +++++++++++-------
> 2 files changed, 11 insertions(+), 15 deletions(-)
>
> diff --git a/include/linux/compiler-clang.h
> b/include/linux/compiler-clang.h
> --- a/include/linux/compiler-clang.h
> +++ b/include/linux/compiler-clang.h
> @@ -15,11 +15,3 @@
> * with any version that can compile the kernel
> */
> #define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix),
> __COUNTER__)
> -
> -/*
> - * GCC does not warn about unused static inline functions for
> - * -Wunused-function. This turns out to avoid the need for complex
> #ifdef
> - * directives. Suppress the warning in clang as well.
> - */
> -#undef inline
> -#define inline inline __attribute__((unused)) notrace
> diff --git a/include/linux/compiler-gcc.h
> b/include/linux/compiler-gcc.h
> --- a/include/linux/compiler-gcc.h
> +++ b/include/linux/compiler-gcc.h
> @@ -66,18 +66,22 @@
>
> /*
> * Force always-inline if the user requests it so via the .config,
> - * or if gcc is too old:
> + * or if gcc is too old.
> + * GCC does not warn about unused static inline functions for
> + * -Wunused-function. This turns out to avoid the need for complex
> #ifdef
> + * directives. Suppress the warning in clang as well by using
> "unused"
> + * function attribute, which is redundant but not harmful for gcc.
> */
> #if !defined(CONFIG_ARCH_SUPPORTS_OPTIMIZED_INLINING) || \
> !defined(CONFIG_OPTIMIZE_INLINING) || (__GNUC__ < 4)
> -#define inline inline __attribute__((always_inline)) notrace
> -#define __inline__ __inline__ __attribute__((always_inline)) notrace
> -#define __inline __inline __attribute__((always_inline)) notrace
> +#define inline inline __attribute__((always_inline,unused)) notrace
> +#define __inline__ __inline__ __attribute__((always_inline,unused))
> notrace
> +#define __inline __inline __attribute__((always_inline,unused))
> notrace
> #else
> /* A lot of inline functions can cause havoc with function tracing */
> -#define inline inline notrace
> -#define __inline__ __inline__ notrace
> -#define __inline __inline notrace
> +#define inline inline __attribute__((unused)) notrace
> +#define __inline__ __inline__ __attribute__((unused)) notrace
> +#define __inline __inline __attribute__((unused)) notrace
> #endif
>
> #define __always_inline inline __attribute__((always_inline))
--
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