2009/7/20 Vegard Nossum <vegard.nos...@gmail.com>:
> We cannot rely on arrays and fields to be smaller than a page in size
> for this test to work, i.e.
>
> byte[] a = null;
> a[4096] = ...;
>
> must still throw NullPointerException.
>
> Signed-off-by: Vegard Nossum <vegard.nos...@gmail.com>
> ---
> include/vm/object.h | 7 ++++++-
> vm/signal.c | 2 +-
> 2 files changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/include/vm/object.h b/include/vm/object.h
> index 9bb4b93..864f7c3 100644
> --- a/include/vm/object.h
> +++ b/include/vm/object.h
> @@ -13,7 +13,10 @@ enum vm_type;
>
> struct vm_object {
> /* For arrays, this points to the array type, e.g. for int arrays,
> - * this points to the (artificial) class named "[I". */
> + * this points to the (artificial) class named "[I". We actually rely
> + * on this being the first field in the struct, because this way we
> + * don't need a null-pointer check for accessing this object whenever
> + * we access ->class first. */
> struct vm_class *class;
>
> pthread_mutex_t mutex;
> @@ -22,6 +25,8 @@ struct vm_object {
> uint8_t fields[];
> };
>
> +/* XXX: BUILD_BUG_ON(offsetof(vm_object, class) != 0); */
> +
> int init_vm_objects(void);
>
> struct vm_object *vm_object_alloc(struct vm_class *class);
> diff --git a/vm/signal.c b/vm/signal.c
> index da2b6d4..cba8460 100644
> --- a/vm/signal.c
> +++ b/vm/signal.c
> @@ -98,7 +98,7 @@ static void sigsegv_handler(int sig, siginfo_t *si, void
> *ctx)
>
> /* Assume that zero-page access is caused by dereferencing a
> null pointer */
> - if ((unsigned long)si->si_addr < (unsigned long)getpagesize()) {
> + if (!si->si_addr) {
> /* We must be extra caucious here because IP might be
> invalid */
> if (get_signal_source_cu(ctx) == NULL)
> --
> 1.6.0.6
>
Acked-by: Tomasz Grabiec <tgrab...@gmail.com>
--
Tomek Grabiec
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