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Destructors not called for c++11 thread_local objects
- From: Ryan Johnson <ryan dot johnson at cs dot utoronto dot ca>
- To: "cygwin at cygwin dot com" <cygwin at cygwin dot com>
- Date: Fri, 01 Aug 2014 13:32:41 -0400
- Subject: Destructors not called for c++11 thread_local objects
- Authentication-results: sourceware.org; auth=none
Hi all,
(Please CC me in replies, I'm not subscribed to the list)
Question: is this a Cygwin bug, gcc bug, or somebody else's bug entirely?
The following STC shows the problem:
$ cat bug.cpp
#include <cstdio>
static thread_local struct X {
int x;
X() { puts("hi"); }
~X() { puts("bye!"); }
} x;
int main() { x.x = 0; }
$ g++ -std=gnu++11 -Wall -g bug.cpp && ./a
hi
A quick inspection of the assembly code shows no call to
__cxa_thread_atexit in __tls_init, where the same code compiled on
linux, with the same version of gcc, has it right. This is odd, because
the function does seem to be available in cygwin's libstdc++:
$ nm /usr/lib/gcc/x86_64-pc-cygwin/4.8.3/libstdc++.a | grep thread_atexit
0000000000000000 d .data$_ZZ19__cxa_thread_atexitE4once
0000000000000000 p .pdata$__cxa_thread_atexit
0000000000000000 t .text$__cxa_thread_atexit
0000000000000000 r .xdata$__cxa_thread_atexit
0000000000000000 T __cxa_thread_atexit
0000000000000000 d _ZZ19__cxa_thread_atexitE4once
Here's the linux version of __tls_init:
__tls_init:
.LFB19:
cmpb $0, %fs:__tls_guard@tpoff
je .L7
rep; ret
.L7:
subq $8, %rsp
movl $.LC1, %edi
movb $1, %fs:__tls_guard@tpoff
call puts
movq %fs:0, %rsi
movl $__dso_handle, %edx
movl $_ZN1XD1Ev, %edi
addq $8, %rsp
addq $_ZL1x@tpoff, %rsi
jmp __cxa_thread_atexit
vs. the same for cygwin:
__tls_init:
subq $40, %rsp
leaq __emutls_v.__tls_guard(%rip), %rcx
call __emutls_get_address
cmpb $0, (%rax)
je .L27
addq $40, %rsp
ret
.L27:
leaq .LC0(%rip), %rcx
movb $1, (%rax)
addq $40, %rsp
jmp puts
Relevant packages installed:
binutils 2.24.51-4
cygwin 1.7.30-1
gcc-core 4.8.3-2
gcc-g++ 4.8.3-2
libstdc++6 4.8.3-2
(I realize I'm a version behind on cygwin1.dll, but I don't think that's
the problem here)
Thoughts?
Ryan
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