linux-kernel - Re: [PATCH] ARM: fix vdsomunge depends on glibc specific byteswap.h

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Date:	Wed, 30 Sep 2015 18:17:52 +0200
From:	Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:	"H. Nikolaus Schaller" <hns@...delico.com>
Cc:	Szabolcs Nagy <szabolcs.nagy@....com>,
	Russell King <rmk+kernel@....linux.org.uk>,
	Nathan Lynch <nathan_lynch@...tor.com>,
	Will Deacon <will.deacon@....com>,
	Marek Belisko <marek@...delico.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] ARM: fix vdsomunge depends on glibc specific byteswap.h

On 30 September 2015 at 18:13, H. Nikolaus Schaller <hns@...delico.com> wrote:
>
> Am 30.09.2015 um 18:02 schrieb Ard Biesheuvel <ard.biesheuvel@...aro.org>:
>
>> On 30 September 2015 at 17:56, H. Nikolaus Schaller <hns@...delico.com> wrote:
>>> If the host toolchain is not glibc based then the arm kernel build
>>> fails with
>>>
>>> HOSTCC  arch/arm/vdso/vdsomunge
>>> arch/arm/vdso/vdsomunge.c:48:22: fatal error: byteswap.h: No such file or directory
>>>
>>> Observed with omap2plus_defconfig and compile on Mac OS X with arm ELF
>>> cross-compiler.
>>>
>>> Reason: byteswap.h is a glibc only header.
>>>
>>> Changed to detect the host and include the right file as described at:
>>>
>>> https://bugs.freedesktop.org/show_bug.cgi?id=8882
>>>
>>> Tested to compile on Mac OS X 10.9.5 host.
>>>
>>> Signed-off-by: H. Nikolaus Schaller <hns@...delico.com>
>>> ---
>>> arch/arm/vdso/vdsomunge.c | 18 ++++++++++++++++++
>>> 1 file changed, 18 insertions(+)
>>>
>>> diff --git a/arch/arm/vdso/vdsomunge.c b/arch/arm/vdso/vdsomunge.c
>>> index aedec81..5364cea 100644
>>> --- a/arch/arm/vdso/vdsomunge.c
>>> +++ b/arch/arm/vdso/vdsomunge.c
>>> @@ -45,7 +45,25 @@
>>> * it does.
>>> */
>>>
>>> +#if defined(__linux__)
>>> #include <byteswap.h>
>>> +#elif defined(__OpenBSD__)
>>> +#include <sys/endian.h>
>>> +#define bswap_16 __swap16
>>> +#define bswap_32 __swap32
>>> +#define bswap_64 __swap64
>>> +#elif defined(__APPLE__)
>>> +#include <libkern/OSByteOrder.h>
>>> +#define bswap_16 OSSwapInt16
>>> +#define bswap_32 OSSwapInt32
>>> +#define bswap_64 OSSwapInt64
>>> +#else
>>> +#include <sys/endian.h>
>>> +#define bswap_16 bswap16
>>> +#define bswap_32 bswap32
>>> +#define bswap_64 bswap64
>>> +#endif
>>> +
>>
>> Have you tried this?
>>
>> #define bswap_16 __builtin_bswap16
>> #define bswap_32 __builtin_bswap32
>> #define bswap_64 __builtin_bswap64
>>
>> https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html
>
> OS X host uses llvm and I am not sure if these builtins are
> always available.
>

I am pretty sure recent clang supports these as well. Could you please try it?

> So it replaces an include file dependency by a compiler
> built-in dependency. IMHO my approach is more general
> and should cover a broader range of compile hosts.
>
> This is a tool compiled by HOSTCC to be run on the build
> host - so I think we can't assume to have a gcc host compiler
> (while for the CC cross-compiler we can).
>

If my suggestion works, we'll support host side GCC and clang without
decorating the source code with lots of #ifdefs for OSes few people
care about. That would be an improvement imo

Thanks,
Ard.
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