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

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Date:	Wed, 30 Sep 2015 18:13:23 +0200
From:	"H. Nikolaus Schaller" <hns@...delico.com>
To:	Ard Biesheuvel <ard.biesheuvel@...aro.org>
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


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.

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).

Thanks,
Nikolaus Schaller

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