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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug sanitizer/114217] -fsanitize=alignment false positive with
 intended unaligned struct member access
Date: Sun, 03 Mar 2024 07:22:10 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D114217

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/inc=
lude/asm-generic/unaligned.h?h=3Dv6.7

is correct except it should not expose get_unaligned/put_unaligned since the
undefined code happens way before.

The problem is with the btrfs code in btrfs_filldir:
```
static int btrfs_filldir(void *addr, int entries, struct dir_context *ctx)
{
        while (entries--) {
                struct dir_entry *entry =3D addr; /// THIS IS BROKEN and ca=
uses
the -fsanitize=3Dalignment error
                char *name =3D (char *)(entry + 1);

                ctx->pos =3D get_unaligned(&entry->offset);
                if (!dir_emit(ctx, name, get_unaligned(&entry->name_len),
                                         get_unaligned(&entry->ino),
                                         get_unaligned(&entry->type)))
                        return 1;
                addr +=3D sizeof(struct dir_entry) +
                        get_unaligned(&entry->name_len);
                ctx->pos++;
        }
        return 0;
}
```

Added comment on where the error comes from. The get_unaligned macro really
should not be used here. What should be used here is an unaligned version of
`struct dir_entry` instead.=