lkml.org 
[lkml]   [2017]   [Jun]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: Using __always_inline attribute
On 2017-06-14 15:33, Sodagudi Prasad wrote:
> On 2017-06-14 03:06, Will Deacon wrote:
>> Hi Prasad,
>>
>> On Tue, Jun 13, 2017 at 03:39:37PM -0700, Sodagudi Prasad wrote:
>>> With a variant of a CLANG(based on 4.0) following errors observed on
>>> Linux
>>> 4.12-rc5 tag.
>>
>> How are you building the kernel with clang, btw? I'd be keen to try
>> the same
>> thing, but I thought the LLVMLinux project was largely dead at his
>> point. Do
>> you still need build system patches, or is this now integrated with
>> Kbuild?
> Hi Will,
> Trying clang patches from below tree -
> https://android.googlesource.com/kernel/common/+/experimental/android-4.4-llvm
>
>>
>>> 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
>>>
>>> Clang does not seems to be marking this macro as inline and causing
>>> above
>>> compilation issue due to BUILD_BUG().
>>
>> The only BUILD_BUG I see around here is if the size parameter (which
>> is
>> calculated using sizeof) is not known to be 1,2,4 or 8 at compile
>> time. It
>> would be interesting to know which call site is confusing clang in
>> this way
>> and what code is actually being emitted here.
>>
>> If it's just that __xchg_mb isn't being inlined into the
>> __xchg_wrapper
>> macro, then your patch should be ok, but I'd like to be sure it's not
>> something else. I'm also surprised you haven't see this crop up in
>> other
>> places.
> After digging further, we observed that inline definition was changed
> recently and causing this issue.
> Here is missing part of inline macro definition
> __attribute__((unused)).
>
> Commit abb2ea7dfd82 ("compiler, clang: suppress warning for unused
> static inline functions") have redefined the inline macro as below
> #define inline inline __attribute__((unused))
>
> But actual definition of inline macro defined compiler-gcc.h file as
> shown below.
> #define inline inline __attribute__((always_inline))
> notrace
>
> As always_inline attribute is missing in inline definition, compile
> may not inline macros __xchg_mb in
> arch/arm64/include/asm/cmpxchg.h file and leading to error.
>
> Some compilers may not honor inline as inline if always_inline
> attribute is removed because of
> -inline-threshold compiler options.
>
> Here is the change to fix this issue-
> diff --git a/include/linux/compiler-clang.h
> b/include/linux/compiler-clang.h
> index d614c5e..a0e6433 100644
> --- a/include/linux/compiler-clang.h
> +++ b/include/linux/compiler-clang.h
> @@ -22,4 +22,4 @@
> * directives. Suppress the warning in clang as well.
> */
> #undef inline
> -#define inline inline __attribute__((unused)) notrace
> +#define inline __attribute__((always_inline)) __attribute__((unused))
> notrace
>
> -Thanks, Prasad

Hi Will,

Here is the proper patch -
compiler, clang: Add always_inline attribute to inline

Commit abb2ea7dfd82 ("compiler, clang: suppress warning for unused
static inline functions") re-defining the 'inline' macro but
__attribute__((always_inline)) is missing. Some compilers may
not honor inline hint if always_iniline attribute is not there.
So add always_inline attribute to inline as done by
compiler-gcc.h file.

diff --git a/include/linux/compiler-clang.h
b/include/linux/compiler-clang.h
index d614c5e..400b0cd 100644
--- a/include/linux/compiler-clang.h
+++ b/include/linux/compiler-clang.h
@@ -22,4 +22,4 @@
* directives. Suppress the warning in clang as well.
*/
#undef inline
-#define inline inline __attribute__((unused)) notrace
+#define inline inline __attribute__((always_inline))
__attribute__((unused)) notrace
-Thanks, Prasad

>>
>> Will

--
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora
Forum,
Linux Foundation Collaborative Project

\
 
 \ /
  Last update: 2017-06-15 02:51    [W:0.259 / U:1.232 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site