Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752832AbdFNWeD (ORCPT ); Wed, 14 Jun 2017 18:34:03 -0400 Received: from smtp.codeaurora.org ([198.145.29.96]:42424 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751600AbdFNWeB (ORCPT ); Wed, 14 Jun 2017 18:34:01 -0400 MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Wed, 14 Jun 2017 15:33:59 -0700 From: Sodagudi Prasad To: Will Deacon Cc: catalin.marinas@arm.com, mingo@kernel.org, peterz@infradead.org, mark.rutland@arm.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: Using __always_inline attribute In-Reply-To: <20170614100641.GB16190@arm.com> References: <2a762f1f3b355e71c5bca6a6e00bffe0@codeaurora.org> <20170614100641.GB16190@arm.com> Message-ID: <9198053a46999b0b46dcab992527d0d7@codeaurora.org> User-Agent: Roundcube Webmail/1.2.5 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2941 Lines: 84 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 > > Will -- The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, Linux Foundation Collaborative Project