Re: [PATCH] linux: mips: Fix getdents64 fallback on mips64-n32

[Florian Weimer <fw@deneb.enyo.de>]

* Adhemerval Zanella via Libc-alpha:

> GCC mainline shows the following error:
>
> ../sysdeps/unix/sysv/linux/mips/mips64/getdents64.c: In function '__getdents64':
> ../sysdeps/unix/sysv/linux/mips/mips64/getdents64.c:121:7: error: 'memcpy' forming offset [4, 7] is out of the bounds [0, 4] [-Werror=array-bounds]
>   121 |       memcpy (((char *) dp + offsetof (struct dirent64, d_ino)),
>       |       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>   122 |               KDP_MEMBER (kdp, d_ino), sizeof ((struct dirent64){0}.d_ino));
>       |               ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> ../sysdeps/unix/sysv/linux/mips/mips64/getdents64.c:123:7: error: 'memcpy' forming offset [4, 7] is out of the bounds [0, 4] [-Werror=array-bounds]
>   123 |       memcpy (((char *) dp + offsetof (struct dirent64, d_off)),
>       |       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>   124 |               KDP_MEMBER (kdp, d_off), sizeof ((struct dirent64){0}.d_off));
>       |               ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> The issue is due both d_ino and d_off fields for mips64-n32
> kernel_dirent are 32-bits, while this is using memcpy to copy 64 bits
> from it into the glibc dirent64.
>
> The fix is to use a temporary variable to read the correct type
> from kernel_dirent.

I think I suggested to cut back on the macro magic and simply have
appropriately defined structs, with a sequence like this:

  memcpy to first temporary struct
  field-by-field assignment from first temporary struct to second struct
  memcpy from second temporary struct

Would that work?

(Sorry if my message got through and this suggestion was already
considered.)