Re: stat64 wrong on sparc64 user

[Laurent Vivier]

Le 28/03/2023 à 14:22, Luca Bonissi a écrit :
> On 28/03/23 13:55, Thomas Huth wrote:
> > On 28/03/2023 13.48, Luca Bonissi wrote:
> > > --- qemu-20230327/linux-user/syscall_defs.h    2023-03-27 15:41:42.000000000 
> > > +0200
> > > +++ qemu-20230327/linux-user/syscall_defs.h.new    2023-03-27 
> > > 21:43:25.615115126 +0200
> > > @@ -1450,7 +1450,7 @@ struct target_stat {
> > >       unsigned int    st_dev;
> > >       abi_ulong    st_ino;
> > >       unsigned int    st_mode;
> > > -    unsigned int    st_nlink;
> > > +    short int    st_nlink;
> > >       unsigned int    st_uid;
> >
> > That looks wrong at a first glance. IIRC Sparc is a very strictly aligned architecture, so if the 
> > previous field "st_mode" was aligned to a 4-byte boundary, the "st_uid" field now would not be 
> > aligned anymore... are you sure about this change? Maybe it needs a padding field now?
>
> The padding is automatic (either on Sparc or x86-64): short will be aligned to 2-byte boundary, int 
> will be aligned to 4-byte boundary, long will be aligned to 8-byte boundary.
>
> E.g.:
> st_dev=0x05060708;
> st_ino=0x1112131415161718;
> st_mode=0x1a1b1c1d;
> st_nlink=0x2728;
> st_uid=0x2a2b2c2d;
> st_gid=0x3a3b3c3d;
> st_rdev=0x35363738;
> st_size=0x4142434445464748;
> st_blksize=0x5152535455565758;
>
> will result (sparc64 - big endian):
> 00: 05 06 07 08 00 00 00 00
> 08: 11 12 13 14 15 16 17 18
> 10: 1A 1B 1C 1D 27 28 00 00
> 18: 2A 2B 2C 2D 3A 3B 3C 3D
> 20: 35 36 37 38 00 00 00 00
> 28: 41 42 43 44 45 46 47 48
> 30: 00 00 00 00 00 00 00 00
> 38: 00 00 00 00 00 00 00 00
> 40: 00 00 00 00 00 00 00 00
> 48: 51 52 53 54 55 56 57 58
> 50: 00 00 00 00 00 00 00 00
> 58: 00 00 00 00 00 00 00 00
> 60: 00 00 00 00 00 00 00 00
>
> Or on x86-64 (little endian):
> 00: 08 07 06 05 00 00 00 00
> 08: 18 17 16 15 14 13 12 11
> 10: 1D 1C 1B 1A 28 27 00 00
> 18: 2D 2C 2B 2A 3D 3C 3B 3A
> 20: 38 37 36 35 00 00 00 00
> 28: 48 47 46 45 44 43 42 41
> 30: 00 00 00 00 00 00 00 00
> 38: 00 00 00 00 00 00 00 00
> 40: 00 00 00 00 00 00 00 00
> 48: 58 57 56 55 54 53 52 51
> 50: 00 00 00 00 00 00 00 00
> 58: 00 00 00 00 00 00 00 00
> 60: 00 00 00 00 00 00 00 00
>
> Please note the automatic padding between "st_dev" and "st_ino" (offset 0x04, 4 bytes), "st_nlink" 
> and "st_uid" (offset 0x16, 2 bytes), "st_rdev" and "st_size" (offset 0x24, 4 bytes).
>
> Placing st_nlink as int would result in incorrect big/little endian conversion, so it should be set 
> as short. If you like clearer source code, you can optionally add padding, but it is not mandatory.

To have automatic alignment according to target ABI, you must use abi_XXX type (see 
include/exec/user/abitypes.h)

For sparc, from the kernel, we have:

struct stat {
        unsigned int st_dev;
        __kernel_ino_t st_ino;
        __kernel_mode_t st_mode;
        short   st_nlink;
        __kernel_uid32_t st_uid;
        __kernel_gid32_t st_gid;
        unsigned int st_rdev;
        long    st_size;
        long    st_atime;
        long    st_mtime;
        long    st_ctime;
        long    st_blksize;
        long    st_blocks;
        unsigned long  __unused4[2];
};

So for the st_link we need to use abi_short.

We can do the same with stat64 and other fields (see 
linux/arch/sparc/include/uapi/asm/stat.h)

Thanks,
Laurent