[PATCH v3] ARM: fix vdsomunge not to depend on glibc specific byteswap.h

[PATCH v3] ARM: fix vdsomunge not to depend on glibc specific byteswap.h

[H. Nikolaus Schaller]

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@goldelico.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..513f9eb 100644
--- a/arch/arm/vdso/vdsomunge.c
+++ b/arch/arm/vdso/vdsomunge.c
@@ -45,7 +45,6 @@
  * it does.
  */
 
-#include <byteswap.h>
 #include <elf.h>
 #include <errno.h>
 #include <fcntl.h>
@@ -59,6 +58,18 @@
 #include <sys/types.h>
 #include <unistd.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)))
+
 #if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
 #define HOST_ORDER ELFDATA2LSB
 #elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
@@ -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

Re: [PATCH v3] ARM: fix vdsomunge not to depend on glibc specific byteswap.h

[Russell King - ARM Linux]

On Thu, Oct 15, 2015 at 07:52:56AM +0200, H. Nikolaus Schaller 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.
> 
> 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@goldelico.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..513f9eb 100644
> --- a/arch/arm/vdso/vdsomunge.c
> +++ b/arch/arm/vdso/vdsomunge.c
> @@ -45,7 +45,6 @@
>   * it does.
>   */
>  
> -#include <byteswap.h>
>  #include <elf.h>
>  #include <errno.h>
>  #include <fcntl.h>
> @@ -59,6 +58,18 @@
>  #include <sys/types.h>
>  #include <unistd.h>
>  
> +#define swab16(x) \
> +	((unsigned short)( \
> +		(((unsigned short)(x) & (unsigned short)0x00ffU) << 8) | \
> +		(((unsigned short)(x) & (unsigned short)0xff00U) >> 8)))

		((((x) & 0x00ff) << 8) | \
		 (((x) & 0xff00) >> 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)))

		((((x) & 0x000000ff) << 24) | \
		 (((x) & 0x0000ff00) <<  8) | \
		 (((x) & 0x00ff0000) >>  8) | \
		 (((x) & 0xff000000) << 24))

We can get rid of all the casts because we know what size 'x' is in
both cases.

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