Use PAGE_MAX_SIZE. PAGE_SIZE is now a variable size.

Use PAGE_MAX_SIZE. PAGE_SIZE is now a variable size.

This fixes exception_handler.cc:77:8: error: fields must have a constant size:
'variable length array in structure' extension will never be supported
  char protected_buffer[PAGE_SIZE] __attribute__((aligned(PAGE_SIZE)));

BUG=None
TEST=breakpad builds on ios8

[justincohen]

This is for iOS8 support.  PTAL!

[Mark Mentovai]

How is PAGE_MAX_SIZE (and PAGE_SIZE) defined now?

[qsr]

On 2014/06/06 15:17:22, Mark Mentovai wrote:
> How is PAGE_MAX_SIZE (and PAGE_SIZE) defined now?

PAGE_SIZE is not vm_page_size which is an extern variable... So we cannot use
this for defining the alignment. Instead they export a constant for the max page
size, that is 16k right now.

[Mark Mentovai]

Well, PAGE_MAX_SIZE isn’t defined in earlier SDKs, so this is going to need a
little more attention.

[justincohen]

#if defined isn't good enough?

[Mark Mentovai]

Well, look at how this struct is used. It’s something that gets mprotected.
mprotect can only protect things with page-level granularity. Is it possible to
build in a situation where PAGE_SIZE is 4k and then find at runtime that the
actual page size is 16k? If you did that, then mprotect would wind up operating
on other data.

On the other hand, if wer’re pretty sure that if you build with an SDK that says
PAGE_SIZE is 4k, your pages will always be 4k, this is OK. LGTM in that case.

Now that I think about it, it’s probably likely that Apple is doing something at
runtime to decide how big your pages can be based on your SDK.

[qsr]

On 2014/06/06 15:54:52, Mark Mentovai wrote:
> Well, look at how this struct is used. It’s something that gets mprotected.
> mprotect can only protect things with page-level granularity. Is it possible
to
> build in a situation where PAGE_SIZE is 4k and then find at runtime that the
> actual page size is 16k? If you did that, then mprotect would wind up
operating
> on other data.
> 
> On the other hand, if wer’re pretty sure that if you build with an SDK that
says
> PAGE_SIZE is 4k, your pages will always be 4k, this is OK. LGTM in that case.
> 
> Now that I think about it, it’s probably likely that Apple is doing something
at
> runtime to decide how big your pages can be based on your SDK.

Mark -> If when I run something that has been compiled with ios 7 SDK, apple
ever give me a page that is biffer than PAGE_SIZE, I'm pretty sure that a lot of
thing will break badly... So I think we are safe (or nothing is...)

[Mark Mentovai]

LGTM

[qsr]

Commited

 Justin, could you close this, I do not have the permission to do it.