Bug 1468807 - glibc: Support broken applications which call __tls_get_addr with an unaligned stack (GCC bug workaround)
Summary: glibc: Support broken applications which call __tls_get_addr with an unaligne...
Alias: None
Product: Red Hat Enterprise Linux 7
Classification: Red Hat
Component: glibc
Version: 7.4
Hardware: x86_64
OS: Unspecified
Target Milestone: rc
: ---
Assignee: Florian Weimer
QA Contact: Sergey Kolosov
Depends On: 1440287
Blocks: 1473718
TreeView+ depends on / blocked
Reported: 2017-07-08 08:10 UTC by Florian Weimer
Modified: 2018-04-10 14:01 UTC (History)
6 users (show)

Fixed In Version: glibc-2.17-210.el7
Doc Type: Enhancement
Doc Text:
Feature: In the slow path of the implementation of __tls_get_addr function in glibc, the stack is automatically aligned as needed. Reason: A bug in the GCC compiler for the x86-64 architecture could sometimes result in a call to the __tls_get_addr function with a misaligned stack, violating ABI requirements. This could result in crashes during TLS access, particularly if an interposed custom malloc is used. Result: Binaries compiled with GCC which suffer from this ABI compliance issue work as expected, even with an interposed custom malloc.
Clone Of: 1440287
Last Closed: 2018-04-10 14:00:52 UTC
Target Upstream Version:

Attachments (Terms of Use)

System ID Priority Status Summary Last Updated
GNU Compiler Collection 58066 None None None 2017-07-08 08:10:41 UTC
Red Hat Bugzilla 1468808 unspecified CLOSED gcc: Call __tls_get_addr with a properly aligned stack on x86-64 2020-10-14 00:28:05 UTC
Red Hat Product Errata RHSA-2018:0805 None None None 2018-04-10 14:01:54 UTC
Sourceware 21609 None None None 2017-07-08 08:10:41 UTC

Internal Links: 1468808

Description Florian Weimer 2017-07-08 08:10:42 UTC
We should consider fixing this in Red Hat Enterprise Linux as well because it is visible with an interposed malloc (which could use vector instructions; the main malloc code in glibc does not when compiled with the system compiler).

+++ This bug was initially created as a clone of Bug #1440287 +++

Description of problem:
Every 64bit game that uses Unity (the game engine) won't start on Fedora 26 (deadlocks on a black screen). 32bit games work fine.


--- Additional comment from Nicholas Miell on 2017-06-17 20:42:52 CEST ---

I'm seeing similar Unity hangs, except the sequence of events is:

1. Thread attempts to lazy init a TLS variable.
2. There is a SIGSEGV in _int_malloc() on a movaps %xmm0,(%rsp) instruction because RSP is misaligned due to https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58066
3. The Mono SIGSEGV handler gets called.
4. The SIGSEGV handler attempts to lazy init a TLS variable.
5. malloc deadlocks.

LD_PRELOADing the following simple stub fixes the affected Unity games:

#include <dlfcn.h>

__attribute__((force_align_arg_pointer)) void *__tls_get_addr (void *ti)
	void *(*tga)(void*) = dlsym(RTLD_NEXT, "__tls_get_addr");

	return tga(ti);

Why doesn't glibc's __tls_get_addr() have this attribute to deal with this gcc bug?

--- Additional comment from Nicholas Miell on 2017-06-17 20:46:21 CEST ---

Actually, the stack traces I'm seeing are literally identical to comment #0, except the signal is definitely SIGSEGV (from a MOVAPS instruction), not SIGPWR (from Mono's garbage collector).

--- Additional comment from Nicholas Miell on 2017-06-17 21:05 CEST ---

unzip align-tls-get-addr.zip
cd align-tls-get-addr
meson BUILD
ninja -C BUILD
LD_PRELOAD=$(pwd)/BUILD/tls_get_addr.so /path/to/bug1440287/repro.x86_64

For Steam, Set Launch Options to LD_PRELOAD=/full/path/to/align-tls-get-addr/BUILD/tls_get_addr.so %command%

--- Additional comment from Nicholas Miell on 2017-06-18 06:44 CEST ---

A proposed patch for glibc.

--- Additional comment from Florian Weimer on 2017-06-18 11:14:28 CEST ---

Thanks for tracking this down.  We will likely use a different approach upstream, involving a compatibility symbol for future glibc versions, and use a sysdeps override for backports.

--- Additional comment from Florian Weimer on 2017-06-29 15:55:49 CEST ---

Upstream patch posted for review: https://sourceware.org/ml/libc-alpha/2017-06/msg00922.html


Comment 1 Florian Weimer 2017-07-08 08:11:55 UTC
Final upstream commit:

commit 031e519c95c069abe4e4c7c59e2b4b67efccdee5
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Thu Jul 6 04:43:06 2017 -0700

    x86-64: Align the stack in __tls_get_addr [BZ #21609]

Comment 8 errata-xmlrpc 2018-04-10 14:00:52 UTC
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.


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