ctypes libffi needs to align the x86 stack to 16 bytes

[gpshead]

BPO	17245
Nosy	@birkenfeld, @gpshead, @larryhastings, @benjaminp
Files	fix_libffi_x86_stack_align.gps01.diff

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/gpshead'
closed_at = <Date 2013-03-20.00:17:19.585>
created_at = <Date 2013-02-19.22:11:10.508>
labels = ['type-crash', 'release-blocker']
title = 'ctypes libffi needs to align the x86 stack to 16 bytes'
updated_at = <Date 2013-03-20.00:17:19.584>
user = 'https://github.com/gpshead'

bugs.python.org fields:

activity = <Date 2013-03-20.00:17:19.584>
actor = 'gregory.p.smith'
assignee = 'gregory.p.smith'
closed = True
closed_date = <Date 2013-03-20.00:17:19.585>
closer = 'gregory.p.smith'
components = []
creation = <Date 2013-02-19.22:11:10.508>
creator = 'gregory.p.smith'
dependencies = []
files = ['29124']
hgrepos = []
issue_num = 17245
keywords = ['patch']
message_count = 3.0
messages = ['182442', '184202', '184713']
nosy_count = 5.0
nosy_names = ['georg.brandl', 'gregory.p.smith', 'larry', 'benjamin.peterson', 'fijall']
pr_nums = []
priority = 'release blocker'
resolution = 'fixed'
stage = 'patch review'
status = 'closed'
superseder = None
type = 'crash'
url = 'https://bugs.python.org/issue17245'
versions = ['Python 2.7', 'Python 3.2', 'Python 3.3', 'Python 3.4']

[gpshead]

The problem: without the stack being 16-byte aligned, code generated by modern compilers like recent gcc/g++ or clang assumed that the stack is 16 byte aligned and uses SSE instructions in some circumstances that require this. Without this fix, any ctypes call into such code will crash.

I mentioned this in the comment on bpo-17192 which seeks to update our ancient copy of libffi but we may want to do this independently of that.

In 2.7, we're running into the stack being misaligned in 32-bit x86 code which is something a libffi update fixes. It is a trivial patch:

http://patchwork.ozlabs.org/patch/58128/

which made it into the official libffi releases in 2010 via atgreen/libffi@3f5b137#src/x86/sysv.S.

patch against 2.7 attached. it should apply to any tree easily enough.

[fijall]

This patch is not in the whatever version ubuntu supplies. Btw, this is code duplication, since there is already darwin alignment, see 17423

[gpshead]

I've updated libffi to v3.0.13 which contains the fixes for this in 2.7, 3.2, 3.3 and 3.4.

if someone wants to apply a surgical patch to fix this problem, the one mentioned above is good as well as:

atgreen/libffi@ee18766

I'm not actually positive that _both_ of those two small libffi patches are needed but they both fix the same thing and it doesn't hurt to have both and both are in the v3.0.13 libffi release.