[PATCH v4] ARM: fix vdsomunge not to depend on glibc specific byteswap.h

[PATCH v4] 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 and kindly improved by Russell King)

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 | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/arch/arm/vdso/vdsomunge.c b/arch/arm/vdso/vdsomunge.c
index aedec81..0cebd98 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 +58,16 @@
 #include <sys/types.h>
 #include <unistd.h>
 
+#define swab16(x) \
+	((((x) & 0x00ff) << 8) | \
+	 (((x) & 0xff00) >> 8))
+
+#define swab32(x) \
+	((((x) & 0x000000ff) << 24) | \
+	 (((x) & 0x0000ff00) <<  8) | \
+	 (((x) & 0x00ff0000) >>  8) | \
+	 (((x) & 0xff000000) << 24))
+
 #if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
 #define HOST_ORDER ELFDATA2LSB
 #elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
@@ -104,17 +113,17 @@ 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

[PATCH v4] ARM: fix vdsomunge not to depend on glibc specific byteswap.h

[Nathan Lynch]

On 10/16/2015 01:38 AM, H. Nikolaus Schaller wrote:
> diff --git a/arch/arm/vdso/vdsomunge.c b/arch/arm/vdso/vdsomunge.c
> index aedec81..0cebd98 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 +58,16 @@
>  #include <sys/types.h>
>  #include <unistd.h>
>  
> +#define swab16(x) \
> +	((((x) & 0x00ff) << 8) | \
> +	 (((x) & 0xff00) >> 8))
> +
> +#define swab32(x) \
> +	((((x) & 0x000000ff) << 24) | \
> +	 (((x) & 0x0000ff00) <<  8) | \
> +	 (((x) & 0x00ff0000) >>  8) | \
> +	 (((x) & 0xff000000) << 24))
> +
>  #if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
>  #define HOST_ORDER ELFDATA2LSB
>  #elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
> @@ -104,17 +113,17 @@ 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;
>  }

I think this looks good now and it checks out in my local testing.
Thanks for your persistence.

Assuming Russell has no further comments I'll put this in his patch
system later today.