Red Hat Bugzilla – Bug 1468807
glibc: Support broken applications which call __tls_get_addr with an unaligned stack (GCC bug workaround)
Last modified: 2017-07-21 15:52:23 EDT
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:
__attribute__((force_align_arg_pointer)) void *__tls_get_addr (void *ti)
void *(*tga)(void*) = dlsym(RTLD_NEXT, "__tls_get_addr");
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 ---
ninja -C BUILD
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
Final upstream commit:
Author: H.J. Lu <firstname.lastname@example.org>
Date: Thu Jul 6 04:43:06 2017 -0700
x86-64: Align the stack in __tls_get_addr [BZ #21609]