Messages in this thread Patch in this message | | | Date | Wed, 14 Jun 2017 17:50:26 -0700 | From | Sodagudi Prasad <> | Subject | Re: Using __always_inline attribute |
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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
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