Hi,

Am 30.09.2015 um 18:17 schrieb Ard Biesheuvel [off-list ref]:

On 30 September 2015 at 18:13, H. Nikolaus Schaller [off-list ref] wrote:

quoted

Am 30.09.2015 um 18:02 schrieb Ard Biesheuvel [off-list ref]:

quoted

On 30 September 2015 at 17:56, H. Nikolaus Schaller [off-list ref] wrote:

quoted

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 <redacted>
---
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?

What release date (= feature set) of a compiler would you no longer consider as "recent"?

quoted

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

Indeed it would be the best solution.

But at least my Apple LLVM version 6.0 (clang-600.0.57) (based on LLVM 3.5svn)
it does *not* work (see also for example http://sourceforge.net/p/flac/bugs/416/ ).

Clang 3.5 appears to provide all features of GCC 4.7.

I have checked and it appears that __builtin_bswap16 only became available in
GCC 4.8 (released 2013-03-22). And maybe in Clang 3.7.

Unfortunately I could not find a reference what the minimum required gcc for
the Linux HOSTCC currently is.

So if we require gcc >= 4.8 just by this small tool, this should be made well
known and well decided.

Therefore I would propose to use the #ifdef approach now and revise 5 years
after gcc 4.8 release (2013 ==> 2018) if __builtin_bswap16 (or something else)
has become a widely available standard.

I can add this to the patch commit V2 for reference.

BR and thanks,
Nikolaus Schaller