Re: [PATCH v3, resend] Fix misaligned accesses to fields in HEADER struct defined in <arpa/nameser_compat.h>

[Andreas Schwab <schwab@linux-m68k.org>]

On Mär 15 2022, John David Anglin wrote:

> diff --git a/resolv/res_mkquery.c b/resolv/res_mkquery.c
> index 5bc5b41531..9b82c82157 100644
> --- a/resolv/res_mkquery.c
> +++ b/resolv/res_mkquery.c
> @@ -193,6 +193,15 @@ context_mkquery_common (struct resolv_context *ctx,
>    return result;
>  }
>  
> +/* The structure HEADER is normally aligned to a word boundary and its
> +   fields are accessed using word loads and stores.  We need to access
> +   this structure when it is aligned on a byte boundary.  This can cause
> +   problems on machines with strict alignment.  So, we create a new
> +   typedef to reduce its alignment to one.  This ensures the fields are
> +   accessed with byte loads and stores.  */
> +typedef HEADER __attribute__ ((__aligned__(1))) UHEADER;
> +#define HEADER UHEADER
> +

The only use of HEADER below that point is in __res_nopt, and AFACS the
only caller __res_context_query always uses aligned memory.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
"And now for something completely different."