[PATCH] squashfs: Fix compilation on big endian systems

[Pali Rohár]

On Thursday 07 April 2022 09:54:21 Miquel Raynal wrote:
> Hi Pali,
> 
> pali at kernel.org wrote on Wed,  6 Apr 2022 23:31:53 +0200:
> 
> Would you mind explaining a little bit how this change fixes it? It
> does not look straightforward to me.

Yes! I though that it is straightforward this change...
byteorder/little_endian.h defines cpu_to_le* macros for Little Endian
systems and byteorder/big_endian.h for Big Endian systems.

File asm/byteorder.h is then ARCH-specific and implements macros for the
current architecture (by including the correct header file).

So currently if you try to compile squashfs for big endian systems you
get compile error:

  In file included from ./arch/powerpc/include/asm/byteorder.h:82,
                   from include/linux/unaligned/access_ok.h:4,
                   from ./arch/powerpc/include/asm/unaligned.h:9,
                   from fs/squashfs/sqfs_filesystem.h:11,
                   from fs/squashfs/sqfs_dir.c:16:
  include/linux/byteorder/big_endian.h:34: warning: "__cpu_to_le32" redefined
   #define __cpu_to_le32(x) ((__force __le32)__swab32((x)))

  In file included from fs/squashfs/sqfs_dir.c:10:
  include/linux/byteorder/little_endian.h:34: note: this is the location of the previous definition
   #define __cpu_to_le32(x) ((__force __le32)(__u32)(x))

Or:

  In file included from fs/squashfs/sqfs.c:14:
  include/linux/byteorder/little_endian.h:89:21: error: redefinition of ‘__be16_to_cpup’
   static inline __u16 __be16_to_cpup(const __be16 *p)
                       ^~~~~~~~~~~~~~
  In file included from ./arch/powerpc/include/asm/byteorder.h:82,
                   from include/linux/unaligned/access_ok.h:4,
                   from ./arch/powerpc/include/asm/unaligned.h:9,
                   from fs/squashfs/sqfs.c:10:
  include/linux/byteorder/big_endian.h:89:21: note: previous definition of ‘__be16_to_cpup’ was here
   static inline __u16 __be16_to_cpup(const __be16 *p)
                       ^~~~~~~~~~~~~~

As some header files include correct asm/byteorder.h file and this
squashfs includes additional little_endian.h.

> > Signed-off-by: Pali Rohár <pali at kernel.org>
> > ---
> >  fs/squashfs/sqfs.c     | 3 +--
> >  fs/squashfs/sqfs_dir.c | 3 +--
> >  2 files changed, 2 insertions(+), 4 deletions(-)
> > 
> > diff --git a/fs/squashfs/sqfs.c b/fs/squashfs/sqfs.c
> > index 5d9c52af80ba..41cb811c1b32 100644
> > --- a/fs/squashfs/sqfs.c
> > +++ b/fs/squashfs/sqfs.c
> > @@ -11,8 +11,7 @@
> >  #include <errno.h>
> >  #include <fs.h>
> >  #include <linux/types.h>
> > -#include <linux/byteorder/little_endian.h>
> > -#include <linux/byteorder/generic.h>
> > +#include <asm/byteorder.h>
> >  #include <memalign.h>
> >  #include <stdlib.h>
> >  #include <string.h>
> > diff --git a/fs/squashfs/sqfs_dir.c b/fs/squashfs/sqfs_dir.c
> > index a265b98fe685..ed83c90682ff 100644
> > --- a/fs/squashfs/sqfs_dir.c
> > +++ b/fs/squashfs/sqfs_dir.c
> > @@ -7,8 +7,7 @@
> >  
> >  #include <errno.h>
> >  #include <linux/types.h>
> > -#include <linux/byteorder/little_endian.h>
> > -#include <linux/byteorder/generic.h>
> > +#include <asm/byteorder.h>
> >  #include <stdint.h>
> >  #include <stdio.h>
> >  #include <stdlib.h>
> 
> Cheers,
> Miquèl