linux-kernel - [PATCH v2] ARM: fix vdsomunge not to depend on glibc specific byteswap.h

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Date:	Sat, 3 Oct 2015 22:46:44 +0200
From:	"H. Nikolaus Schaller" <hns@...delico.com>
To:	Szabolcs Nagy <szabolcs.nagy@....com>,
	Russell King <rmk+kernel@....linux.org.uk>,
	Nathan Lynch <nathan_lynch@...tor.com>,
	Will Deacon <will.deacon@....com>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	marek@...delico.com
Subject: [PATCH v2] ARM: fix vdsomunge not to depend on glibc specific byteswap.h

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.

Solution: replace by private byte-swapping macros (taken from
arch/mips/boot/elf2ecoff.c)

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 | 19 +++++++++++++++----
1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/arch/arm/vdso/vdsomunge.c b/arch/arm/vdso/vdsomunge.c
index aedec81..27a9a0b 100644
--- a/arch/arm/vdso/vdsomunge.c
+++ b/arch/arm/vdso/vdsomunge.c
@@ -45,7 +45,18 @@
 * it does.
 */

-#include <byteswap.h>
+#define swab16(x) \
+	((unsigned short)( \
+		(((unsigned short)(x) & (unsigned short)0x00ffU) << 8) | \
+		(((unsigned short)(x) & (unsigned short)0xff00U) >> 8) ))
+
+#define swab32(x) \
+	((unsigned int)( \
+		(((unsigned int)(x) & (unsigned int)0x000000ffUL) << 24) | \
+		(((unsigned int)(x) & (unsigned int)0x0000ff00UL) <<  8) | \
+		(((unsigned int)(x) & (unsigned int)0x00ff0000UL) >>  8) | \
+		(((unsigned int)(x) & (unsigned int)0xff000000UL) >> 24) ))
+
#include <elf.h>
#include <errno.h>
#include <fcntl.h>
@@ -104,17 +115,17 @@ static void cleanup(void)

static Elf32_Word read_elf_word(Elf32_Word word, bool swap)
{
-	return swap ? bswap_32(word) : word;
+	return swap ? swab32(word) : word;
}

static Elf32_Half read_elf_half(Elf32_Half half, bool swap)
{
-	return swap ? bswap_16(half) : half;
+	return swap ? swab16(half) : half;
}

static void write_elf_word(Elf32_Word val, Elf32_Word *dst, bool swap)
{
-	*dst = swap ? bswap_32(val) : val;
+	*dst = swap ? swab32(val) : val;
}

int main(int argc, char **argv)
-- 
2.5.1

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