Re: [PATCH v2 1/2] compiler-gcc.h: add gnu_inline to all inline declarations

From: Sedat Dilek <sedat.dilek@gmail.com>
To: hpa@zytor.com
Cc: Joe Perches <joe@perches.com>,
	Nick Desaulniers <ndesaulniers@google.com>,
	akpm@linux-foundation.org, ard.biesheuvel@linaro.org,
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	boris.ostrovsky@oracle.com, brijesh.singh@amd.com,
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	michal.lkml@markovi.net, linux-kbuild@vger.kernel.org,
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	mawilcox@microsoft.com, Arnd Bergmann <arnd@arndb.de>,
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Subject: Re: [PATCH v2 1/2] compiler-gcc.h: add gnu_inline to all inline declarations
Date: Fri, 8 Jun 2018 16:34:50 +0200	[thread overview]
Message-ID: <CA+icZUUz1Zb1e0LbeccY-3=HY02txe4BiNwhN0vqW_RkQpfLCw@mail.gmail.com> (raw)
In-Reply-To: <5C97550D-BEF4-4069-9373-F7543E3878FB@zytor.com>

On Wed, Jun 6, 2018 at 6:39 PM,  <hpa@zytor.com> wrote:
...
>>Beyond this, a general question: Can someone explain why all these
>>inline defines are in compiler-gcc.h (as there exists compiler.h and
>>compiler-clang.h)?
>>
>>Thanks.
>>
>>Regards,
>>- Sedat -
>
> Because gcc itself also supports both GNU89-style and C99-style inlines, but the kernel was built with the former, and it is not necessarily a trivial modification, except for "static inline" which is the same for both.
>
> The other option is to pass -fgnu89-inline on the command line, which is supported by both gcc and clang. The two methods are fully equivalent.
>

We have...

$ ls include/linux/compiler*
include/linux/compiler-clang.h  include/linux/compiler-gcc.h
include/linux/compiler.h  include/linux/compiler-intel.h
include/linux/compiler_types.h

include/linux/compiler_types.h says...

#ifdef __GNUC__
#include <linux/compiler-gcc.h>
#endif
...
/* Intel compiler defines __GNUC__. So we will overwrite implementations
 * coming from above header files here
 */
#ifdef __INTEL_COMPILER
# include <linux/compiler-intel.h>
#endif

/* Clang compiler defines __GNUC__. So we will overwrite implementations
 * coming from above header files here
 */
#ifdef __clang__
#include <linux/compiler-clang.h>
#endif

/*
 * Generic compiler-dependent macros required for kernel
 * build go below this comment. Actual compiler/compiler version
 * specific implementations come from the above header files
 */
...

include/linux/compiler-clang.h says...

#ifndef __LINUX_COMPILER_TYPES_H
#error "Please don't include <linux/compiler-clang.h> directly,
include <linux/compiler.h> instead."
#endif

So, compiler-clang.h uses defines etc. from compiler-gcc.h but might
overwrite it.
Correct?
I would have expected inline defines in compiler.h as I thought there
is the place for generic stuff.

Maybe you can clarify on the roles of especially compiler.h and
compiler_types.h.

Thanks.

- sed@ -