Re: [PATCH] squashfs: Fix compilation on big endian systems

[Miquel Raynal <miquel.raynal@bootlin.com>]

Hi Pali,

pali@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@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?

> 
> > > Signed-off-by: Pali Rohár <pali@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