asan: Don’t pad the CrashpadInfo struct with a red zone

asan: Don’t pad the CrashpadInfo struct with a red zone

MachOImageReader::GetCrashpadInfo() expects the CrashpadInfo struct to
be the only thing in a __DATA,__crashpad_info section, and enforces this
by checking that the section’s size matches the size declared in the
struct’s size_ field.

Under AddressSanitizer, a red zone follows the structure. While not
reflected in the size of the structure, it is reflected in the size of
the section, causing MachOImageReader::GetCrashpadInfo() to reject the
CrashpadInfo on the assumption that something else is present in the
section.

By specifying an alignment greater than the minimum red zone size of 32
bytes, red zone generation can be suppressed.

TEST=crashpad_snapshot_test
BUG=crashpad:44
R=glider@chromium.org, rsesek@chromium.org

Committed: https://chromium.googlesource.com/crashpad/crashpad/+/f21b7401713c3bda50d747d3c13d27136bcc6030

[Mark Mentovai, 2015-08-20 14:34:41]

mark@chromium.org changed reviewers:
+ glider@chromium.org, rsesek@chromium.org

[Robert Sesek, 2015-08-20 14:52:01]

LGTM. If we need to do this more than once, maybe create a macro like
ALIGN_TO_AVOID_ASAN_REDZONE ?

[Alexander Potapenko, 2015-08-20 15:04:39]

On 2015/08/20 14:52:01, Robert Sesek wrote:
> LGTM. If we need to do this more than once, maybe create a macro like
> ALIGN_TO_AVOID_ASAN_REDZONE ?

I should have noted that setting the alignment to 64 to avoid ASan redzone may
break in future, because in theory nothing should prevent ASan from adding
redzones to aligned globals.
Perhaps using a blacklist is a bit cleaner.

[Mark Mentovai, 2015-08-20 15:13:28]

The blacklist is a bit more hairy build work. I was hoping an attribute or
pragma in the .cc file would do the trick.

[Alexander Potapenko, 2015-08-20 15:17:41]

On 2015/08/20 15:13:28, Mark Mentovai - out til August wrote:
> The blacklist is a bit more hairy build work. I was hoping an attribute or
> pragma in the .cc file would do the trick.

There's no attribute for that yet.
Perhaps we can add one someday or change the default behavior for user-defined
sections.
I don't expect for the alignment hack to stop working anytime soon, so LGTM.

[Mark Mentovai, 2015-08-20 16:40:27]

Thanks. If you do come up with an attribute for this, please let me know and
I’ll happily switch to it. (Or if there’s a bug filed for something like that, I
can at least link to it in the comment.)

[Mark Mentovai, 2015-08-20 18:10:47]

Committed patchset #1 (id:1) manually as
f21b7401713c3bda50d747d3c13d27136bcc6030 (presubmit successful).