On 11/26/2015 10:45 AM, Martin Sebor wrote:
On 11/26/2015 04:33 AM, Ramana Radhakrishnan wrote:
Cookies on ARM are 8-bytes [1], but sizeof ((size_t) n) is only 4-bytes,
so this check will fail (We'll ask for 500 bytes, the test here will
only
be looking for 496).
Would it undermine the test for other architectures if I were to swap
out
the != for a >= ? I think that is in line with the "argument large
enough
for the array" that this test is looking for, but would not catch
bugs where
we were allocating more memory than neccessary.
Otherwise I can spin a patch which skips the test for ARM targets.
I didn't want to skip this for ARM, instead something that takes into
account the cookie size - (very gratuitous hack was to just add 4 in a
#ifdef __arm__ block). Something like attached, brown paper bag
warning ;)
Thanks. I'll commit it today after some testing.
I've checked in a slightly modified version of your patch in r230987.
I should probably also check to see if there are other such targets
and try to find a way to generalize the test. (There should be a way
to expose the cookie size to programs, otherwise they have no way to
avoid buffer overflow in array forms of placement new).
There don't appear to be other targets besides ARM that override
the default cookie size. I opened enhancement c++/68571 - provide
__builtin_cookie_size, to provide an API to make it possible for
programs to query this constant.
Martin
