[PATCH] squashfs: Fix compilation on big endian systems

[Pali Rohár]

On Thursday 07 April 2022 11:54:55 Miquel Raynal wrote:
> Hi Pali,
> 
> pali at kernel.org wrote on Thu, 7 Apr 2022 11:41:59 +0200:
> 
> > 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.
> 
> Great, thanks for the thorough explanation. Based on what you said,
> wouldn't it be cleaner to just get rid of the little_endian.h include
> rather than also use the ARCH specific byteorder.h header?

I think that this is not possible. squashfs code uses le16_to_cpu()
macro and its correct definition is provided only by arch specific
asm/byteorder.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  
> 
> 
> Thanks,
> Miquèl