ext4: add nonstring annotations to ext4.h

This suppresses some false positives in gcc 8's -Wstringop-truncation

Suggested by Miguel Ojeda (hopefully the __nonstring definition will
eventually get accepted in the compiler-gcc.h header file).

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
---
 fs/ext4/ext4.h | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

Hi Ted,

On Mon, Aug 27, 2018 at 7:23 AM, Theodore Ts'o <tytso@mit.edu> wrote:
> This suppresses some false positives in gcc 8's -Wstringop-truncation
>
> Suggested by Miguel Ojeda (hopefully the __nonstring definition will
> eventually get accepted in the compiler-gcc.h header file).

Thank you for checking it out! Whenever this gets merged, I will
update the __nonstring series with the #ifdef cleanup (as a second
example for the series and to avoid you worrying about the cleanup :-)

Cheers,
Miguel

>
> Signed-off-by: Theodore Ts'o <tytso@mit.edu>
> Cc: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
> ---
>  fs/ext4/ext4.h | 17 ++++++++++++++---
>  1 file changed, 14 insertions(+), 3 deletions(-)
>
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 1fc013f3d944..249bcee4d7b2 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -43,6 +43,17 @@
>  #define __FS_HAS_ENCRYPTION IS_ENABLED(CONFIG_EXT4_FS_ENCRYPTION)
>  #include <linux/fscrypt.h>
>
> +#include <linux/compiler.h>
> +
> +/* Until this gets included into linux/compiler-gcc.h */
> +#ifndef __nonstring
> +#if defined(GCC_VERSION) && (GCC_VERSION >= 80000)
> +#define __nonstring __attribute__((nonstring))
> +#else
> +#define __nonstring
> +#endif
> +#endif
> +
>  /*
>   * The fourth extended filesystem constants/structures
>   */
> @@ -1226,7 +1237,7 @@ struct ext4_super_block {
>         __le32  s_feature_ro_compat;    /* readonly-compatible feature set */
>  /*68*/ __u8    s_uuid[16];             /* 128-bit uuid for volume */
>  /*78*/ char    s_volume_name[16];      /* volume name */
> -/*88*/ char    s_last_mounted[64];     /* directory where last mounted */
> +/*88*/ char    s_last_mounted[64] __nonstring; /* directory where last mounted */
>  /*C8*/ __le32  s_algorithm_usage_bitmap; /* For compression */
>         /*
>          * Performance hints.  Directory preallocation should only
> @@ -1277,13 +1288,13 @@ struct ext4_super_block {
>         __le32  s_first_error_time;     /* first time an error happened */
>         __le32  s_first_error_ino;      /* inode involved in first error */
>         __le64  s_first_error_block;    /* block involved of first error */
> -       __u8    s_first_error_func[32]; /* function where the error happened */
> +       __u8    s_first_error_func[32] __nonstring;     /* function where the error happened */
>         __le32  s_first_error_line;     /* line number where error happened */
>         __le32  s_last_error_time;      /* most recent time of an error */
>         __le32  s_last_error_ino;       /* inode involved in last error */
>         __le32  s_last_error_line;      /* line number where error happened */
>         __le64  s_last_error_block;     /* block involved of last error */
> -       __u8    s_last_error_func[32];  /* function where the error happened */
> +       __u8    s_last_error_func[32] __nonstring;      /* function where the error happened */
>  #define EXT4_S_ERR_END offsetof(struct ext4_super_block, s_mount_opts)
>         __u8    s_mount_opts[64];
>         __le32  s_usr_quota_inum;       /* inode for tracking user quota */
> --
> 2.18.0.rc0
>

On Mon, Aug 27, 2018 at 02:07:04PM +0200, Miguel Ojeda wrote:
> 
> Thank you for checking it out! Whenever this gets merged, I will
> update the __nonstring series with the #ifdef cleanup (as a second
> example for the series and to avoid you worrying about the cleanup :-)

Thank you for suggesting it!

Cheers,

						- Ted