linux-kernel - Re: Commit bc27fb68aaad4 breaks qemu build

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Date:	Tue, 29 Mar 2016 14:11:35 -0400
From:	Josh Boyer <jwboyer@...oraproject.org>
To:	Denys Vlasenko <dvlasenk@...hat.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>
Subject: Re: Commit bc27fb68aaad4 breaks qemu build

Adding lkml, which I forgot to do in my original email.

On Tue, Mar 29, 2016 at 2:05 PM, Denys Vlasenko <dvlasenk@...hat.com> wrote:
> On 03/29/2016 02:41 PM, Josh Boyer wrote:
>> Hello,
>>
>> We've had a report[1] that the changes to include/uapi/linux/swab.h
>> breaks the build for qemu.  This appears to be because the
>> __always_inline attribute is added to some of the definitions in a
>> uapi header, but that attribute itself is defined in
>> include/linux/compiler.h (compiler-gcc.h to be specific).  The
>> compiler.h header isn't exported to userspace via the uapi mechanism
>> which means __always_inline isn't defined.
>>
>> There are likely two options here.  The first is to revert the change,
>> but that breaks busybox or something.  The second is to use the
>> definition of __always_inline itself in the uapi headers, specifying
>> "inline __attribute__((always_inline)) explicitly.  There might be
>> other solutions, but at the moment things seem broken.
>>
>> Opinions?
>
> I propose moving this block in compiler.h:
>
> #ifndef __always_inline
> #define __always_inline inline
> #endif
>
> #endif /* __KERNEL__ */
>
> to sit outside of __KERNEL__ guard. Sending a patch shortly.

I'm not sure that will work.  As I said, include/linux/compiler.h (and
all variants of that) are not exported by uapi.  So whatever you do in
those files won't be reflected on anything installed in
/usr/include/linux afaik.

josh