armv6 specific std::async crash from g++6 built a.out [stable/11 -r304943 context; /usr/ports -r421001 context]
Mark Millard
markmi at dsl-only.net
Thu Sep 1 14:53:09 UTC 2016
[I've only compared armv6 and amd64 behavior for this. amd64 did not get the problem.]
The program is under 40 lines and is shown below:
(It is a simplification of the context of the original discovery.)
> # more g++6_build_crashes.cpp
> #include <vector> // vector
> #include <future> // future, async, launch::async
> #include <thread> // thread::hardware_concurrency
>
> decltype(std::thread::hardware_concurrency()) static parallel_count{0u};
>
> static void take_time_measurements() {}
>
> int main(int, const char* [])
> {
> parallel_count = std::thread::hardware_concurrency();
> // Do not presume more threads than this are possible.
>
> if (1 < parallel_count)
> {
> --parallel_count; // leave room for main's thread.
>
> std::vector<std::future<void>> parallels{};
> parallels.reserve(parallel_count);
>
> parallels.emplace_back
> ( std::async( std::launch::async, take_time_measurements ) );
>
> parallels.emplace_back
> ( std::async( std::launch::async, take_time_measurements ) );
>
> for (auto const& at : parallels)
> { at.wait(); }
>
> for (auto& at : parallels)
> { at.get(); }
> }
> return 0;
> }
I do not know if the problem is a bad interaction between FreeBSD's -pthread and g++6's library code vs. if this is strictly a g++6 library problem somehow specific to armv6.
g++6 based builds run fine in my amd64 context (FreeBSD stable/11 under VirtualBox under Mac OS X).
The clang++ 3.8.0 system compiler based build works fine on both amd64 and armv6 (an rpi2).
Builds via g++6 on the rpi2 produce an a.out that fails as shown below (SIGSEGV):
> # /usr/local/bin/gdb ./a.out
> GNU gdb (GDB) 7.11.1 [GDB v7.11.1 for FreeBSD]
> Copyright (C) 2016 Free Software Foundation, Inc.
> License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
> This is free software: you are free to change and redistribute it.
> There is NO WARRANTY, to the extent permitted by law. Type "show copying"
> and "show warranty" for details.
> This GDB was configured as "armv6-portbld-freebsd11.0".
> Type "show configuration" for configuration details.
> For bug reporting instructions, please see:
> <http://www.gnu.org/software/gdb/bugs/>.
> Find the GDB manual and other documentation resources online at:
> <http://www.gnu.org/software/gdb/documentation/>.
> For help, type "help".
> Type "apropos word" to search for commands related to "word"...
> Reading symbols from ./a.out...done.
> (gdb) run
> Starting program: /root/c_tests/a.out
> [New LWP 100255 of process 12266]
>
> Thread 2 received signal SIGSEGV, Segmentation fault.
> [Switching to LWP 100255 of process 12266]
> 0x00000000 in ?? ()
> (gdb) bt
> #0 0x00000000 in ?? ()
> #1 0x200b2acc in _pthread_once (once_control=<optimized out>, init_routine=<optimized out>) at /usr/src/lib/libthr/thread/thr_once.c:95
> #2 0x0001312c in __gthread_once (__func=<optimized out>, __once=0x20824024) at /usr/local/lib/gcc6/include/c++/armv6-portbld-freebsd11.0/bits/gthr-default.h:699
> #3 std::call_once<void (std::__future_base::_State_baseV2::*)(std::function<std::unique_ptr<std::__future_base::_Result_base, std::__future_base::_Result_base::_Deleter> ()>*, bool*), std::__future_b
> ase::_State_baseV2*, std::function<std::unique_ptr<std::__future_base::_Result_base, std::__future_base::_Result_base::_Deleter> ()>*, bool*>(std::once_flag&, void (std::__future_base::_State_baseV2::
> *&&)(std::function<std::unique_ptr<std::__future_base::_Result_base, std::__future_base::_Result_base::_Deleter> ()>*, bool*), std::__future_base::_State_baseV2*&&, std::function<std::unique_ptr<std::
> __future_base::_Result_base, std::__future_base::_Result_base::_Deleter> ()>*&&, bool*&&) (__f=<optimized out>, __once=...) at /usr/local/lib/gcc6/include/c++/mutex:619
> #4 std::__future_base::_State_baseV2::_M_set_result(std::function<std::unique_ptr<std::__future_base::_Result_base, std::__future_base::_Result_base::_Deleter> ()>, bool) (__ignore_failure=false,
> __res=..., this=0x2082400c) at /usr/local/lib/gcc6/include/c++/future:393
> #5 std::__future_base::_Async_state_impl<std::_Bind_simple<void (*())()>, void>::_Async_state_impl(std::_Bind_simple<void (*())()>&&)::{lambda()#1}::operator()() const (__closure=0x2082500c)
> at /usr/local/lib/gcc6/include/c++/future:1664
> #6 std::_Bind_simple<std::__future_base::_Async_state_impl<std::_Bind_simple<void (*())()>, void>::_Async_state_impl(std::_Bind_simple<void (*())()>&&)::{lambda()#1} ()>::_M_invoke<>(std::_Index_tupl
> e<>) (this=0x2082500c) at /usr/local/lib/gcc6/include/c++/functional:1400
> #7 std::_Bind_simple<std::__future_base::_Async_state_impl<std::_Bind_simple<void (*())()>, void>::_Async_state_impl(std::_Bind_simple<void (*())()>&&)::{lambda()#1} ()>::operator()() (
> this=0x2082500c) at /usr/local/lib/gcc6/include/c++/functional:1389
> #8 std::thread::_State_impl<std::_Bind_simple<std::__future_base::_Async_state_impl<std::_Bind_simple<void (*())()>, void>::_Async_state_impl(std::_Bind_simple<void (*())()>&&)::{lambda()#1} ()> >::_
> M_run() (this=0x20825008) at /usr/local/lib/gcc6/include/c++/thread:196
> #9 0x201ac464 in std::execute_native_thread_routine (__p=0x20825008) at /usr/obj/portswork/usr/ports/lang/gcc6/work/gcc-6.2.0/libstdc++-v3/src/c++11/thread.cc:83
> #10 0x200a9fd4 in thread_start (curthread=<optimized out>) at /usr/src/lib/libthr/thread/thr_create.c:289
> #11 0x200a9a90 in _pthread_create (thread=0xbfbfecbc, attr=<optimized out>, start_routine=<optimized out>, arg=<optimized out>) at /usr/src/lib/libthr/thread/thr_create.c:185
> #12 0x201ac724 in __gthread_create (__args=<optimized out>, __func=0x201ac450 <std::execute_native_thread_routine(void*)>, __threadid=0xbfbfec84)
> at /usr/obj/portswork/usr/ports/lang/gcc6/work/.build/armv6-portbld-freebsd11.0/libstdc++-v3/include/armv6-portbld-freebsd11.0/bits/gthr-default.h:662
> #13 std::thread::_M_start_thread (this=this at entry=0xbfbfecb4, state=std::unique_ptr<std::thread::_State> containing 0x20825018)
> at /usr/obj/portswork/usr/ports/lang/gcc6/work/gcc-6.2.0/libstdc++-v3/src/c++11/thread.cc:163
> #14 0x000138ec in std::thread::thread<std::__future_base::_Async_state_impl<std::_Bind_simple<void (*())()>, void>::_Async_state_impl(std::_Bind_simple<void (*())()>&&)::{lambda()#1}>(std::__future_ba
> se::_Async_state_impl<std::_Bind_simple<void (*())()>, void>::_Async_state_impl(std::_Bind_simple<void (*())()>&&)::{lambda()#1}&&) (__f=<optimized out>, this=0xbfbfecb4)
> at /usr/local/lib/gcc6/include/c++/thread:136
> #15 std::__future_base::_Async_state_impl<std::_Bind_simple<void (*())()>, void>::_Async_state_impl(std::_Bind_simple<void (*())()>&&) (__fn=<optimized out>, this=0x2082404c)
> at /usr/local/lib/gcc6/include/c++/future:1661
> #16 __gnu_cxx::new_allocator<std::__future_base::_Async_state_impl<std::_Bind_simple<void (*())()>, void> >::construct<std::__future_base::_Async_state_impl<std::_Bind_simple<void (*())()>, void>, std
> ::_Bind_simple<void (*())()> >(std::__future_base::_Async_state_impl<std::_Bind_simple<void (*())()>, void>*, std::_Bind_simple<void (*())()>&&) (this=<optimized out>, __p=<optimized out>)
> at /usr/local/lib/gcc6/include/c++/ext/new_allocator.h:120
> #17 std::allocator_traits<std::allocator<std::__future_base::_Async_state_impl<std::_Bind_simple<void (*())()>, void> > >::construct<std::__future_base::_Async_state_impl<std::_Bind_simple<void (*())(
> )>, void>, std::_Bind_simple<void (*())()> >(std::allocator<std::__future_base::_Async_state_impl<std::_Bind_simple<void (*())()>, void> >&, std::__future_base::_Async_state_impl<std::_Bind_simple<voi
> d (*())()>, void>*, std::_Bind_simple<void (*())()>&&) (__a=..., __p=<optimized out>) at /usr/local/lib/gcc6/include/c++/bits/alloc_traits.h:455
> #18 std::_Sp_counted_ptr_inplace<std::__future_base::_Async_state_impl<std::_Bind_simple<void (*())()>, void>, std::allocator<std::__future_base::_Async_state_impl<std::_Bind_simple<void (*())()>, voi
> d> >, (__gnu_cxx::_Lock_policy)2>::_Sp_counted_ptr_inplace<std::_Bind_simple<void (*())()> >(std::allocator<std::__future_base::_Async_state_impl<std::_Bind_simple<void (*())()>, void> >, std::_Bind_s
> imple<void (*())()>&&) (__a=..., this=0x20824040) at /usr/local/lib/gcc6/include/c++/bits/shared_ptr_base.h:520
> #19 std::__shared_count<(__gnu_cxx::_Lock_policy)2>::__shared_count<std::__future_base::_Async_state_impl<std::_Bind_simple<void (*())()>, void>, std::allocator<std::__future_base::_Async_state_impl<s
> td::_Bind_simple<void (*())()>, void> >, std::_Bind_simple<void (*())()> >(std::_Sp_make_shared_tag, std::__future_base::_Async_state_impl<std::_Bind_simple<void (*())()>, void>*, std::allocator<std::
> __future_base::_Async_state_impl<std::_Bind_simple<void (*())()>, void> > const&, std::_Bind_simple<void (*())()>&&) (__a=..., this=<optimized out>)
> at /usr/local/lib/gcc6/include/c++/bits/shared_ptr_base.h:615
> #20 std::__shared_ptr<std::__future_base::_Async_state_impl<std::_Bind_simple<void (*())()>, void>, (__gnu_cxx::_Lock_policy)2>::__shared_ptr<std::allocator<std::__future_base::_Async_state_impl<std::
> _Bind_simple<void (*())()>, void> >, std::_Bind_simple<void (*())()> >(std::_Sp_make_shared_tag, std::allocator<std::__future_base::_Async_state_impl<std::_Bind_simple<void (*())()>, void> > const&, s
> td::_Bind_simple<void (*())()>&&) (__a=..., __tag=..., this=<optimized out>) at /usr/local/lib/gcc6/include/c++/bits/shared_ptr_base.h:1100
> #21 std::shared_ptr<std::__future_base::_Async_state_impl<std::_Bind_simple<void (*())()>, void> >::shared_ptr<std::allocator<std::__future_base::_Async_state_impl<std::_Bind_simple<void (*())()>, voi
> d> >, std::_Bind_simple<void (*())()> >(std::_Sp_make_shared_tag, std::allocator<std::__future_base::_Async_state_impl<std::_Bind_simple<void (*())()>, void> > const&, std::_Bind_simple<void (*())()>&
> &) (__a=..., __tag=..., this=<optimized out>) at /usr/local/lib/gcc6/include/c++/bits/shared_ptr.h:319
> #22 std::allocate_shared<std::__future_base::_Async_state_impl<std::_Bind_simple<void (*())()>, void>, std::allocator<std::__future_base::_Async_state_impl<std::_Bind_simple<void (*())()>, void> >, st
> d::_Bind_simple<void (*())()> >(std::allocator<std::__future_base::_Async_state_impl<std::_Bind_simple<void (*())()>, void> > const&, std::_Bind_simple<void (*())()>&&) (__a=...)
> at /usr/local/lib/gcc6/include/c++/bits/shared_ptr.h:620
> #23 std::make_shared<std::__future_base::_Async_state_impl<std::_Bind_simple<void (*())()>, void>, std::_Bind_simple<void (*())()> >(std::_Bind_simple<void (*())()>&&) ()
> at /usr/local/lib/gcc6/include/c++/bits/shared_ptr.h:636
> #24 std::__future_base::_S_make_async_state<std::_Bind_simple<void (*())()> >(std::_Bind_simple<void (*())()>&&) (__fn=<optimized out>) at /usr/local/lib/gcc6/include/c++/future:1702
> #25 std::async<void (&)()> (__policy=__policy at entry=std::launch::async, __fn=@0x120d8: {void (void)} 0x120d8 <take_time_measurements()>) at /usr/local/lib/gcc6/include/c++/future:1716
> #26 0x00011788 in main () at g++6_build_crashes.cpp:25
> (gdb)
Context:
> # uname -apKU
> FreeBSD rpi2 11.0-PRERELEASE FreeBSD 11.0-PRERELEASE #5 r304943M: Sun Aug 28 03:17:54 PDT 2016 markmi at FreeBSDx64:/usr/obj/clang/arm.armv6/usr/src/sys/RPI2-NODBG arm armv6 1100502 1100502
> # svnlite info /usr/src | grep "Re[vl][ai:]"
> Relative URL: ^/stable/11
> Revision: 304943
> Last Changed Rev: 304943
> # svnlite info /usr/ports | grep "Re[vl][ai:]"
> Relative URL: ^/head
> Revision: 421001
> Last Changed Rev: 421001
> # more /etc/make.conf
> DEFAULT_VERSIONS+=perl5=5.22
> WRKDIRPREFIX=/usr/obj/portswork
> WITH_DEBUG=
> WITH_DEBUG_FILES=
> MALLOC_PRODUCTION=
The compiler -v output is shown in the below:
(Removing the -mcpu=cortex-a7 still gets the problem. Using -O0 instead of -O2 also still gets the problem.)
> Script started on Thu Sep 1 06:52:45 2016
> Command: g++6 -g -v -std=c++14 -Wpedantic -Wall -O2 -pthread -Wl,-rpath=/usr/local/lib/gcc6 -mcpu=cortex-a7 g++6_build_crashes.cpp
> Using built-in specs.
> COLLECT_GCC=g++6
> COLLECT_LTO_WRAPPER=/usr/local/libexec/gcc6/gcc/armv6-portbld-freebsd11.0/6.2.0/lto-wrapper
> Target: armv6-portbld-freebsd11.0
> Configured with: /usr/obj/portswork/usr/ports/lang/gcc6/work/gcc-6.2.0/configure --disable-multilib --disable-bootstrap --disable-nls --enable-gnu-indirect-function --libdir=/usr/local/lib/gcc6 --libe
> xecdir=/usr/local/libexec/gcc6 --program-suffix=6 --with-as=/usr/local/bin/as --with-gmp=/usr/local --with-gxx-include-dir=/usr/local/lib/gcc6/include/c++/ --with-ld=/usr/local/bin/ld --with-pkgversio
> n='FreeBSD Ports Collection' --with-system-zlib --disable-libgcj --enable-languages=c,c++,objc,fortran --prefix=/usr/local --localstatedir=/var --mandir=/usr/local/man --infodir=/usr/local/info/gcc6 -
> -build=armv6-portbld-freebsd11.0
> Thread model: posix
> gcc version 6.2.0 (FreeBSD Ports Collection)
> COLLECT_GCC_OPTIONS='-g' '-v' '-std=c++14' '-Wpedantic' '-Wall' '-O2' '-pthread' '-mcpu=cortex-a7' '-shared-libgcc' '-mtls-dialect=gnu'
> /usr/local/libexec/gcc6/gcc/armv6-portbld-freebsd11.0/6.2.0/cc1plus -quiet -v g++6_build_crashes.cpp -quiet -dumpbase g++6_build_crashes.cpp -mcpu=cortex-a7 -mtls-dialect=gnu -auxbase g++6_build_cras
> hes -g -O2 -Wpedantic -Wall -std=c++14 -version -o /tmp//cc0nzkwI.s
> GNU C++14 (FreeBSD Ports Collection) version 6.2.0 (armv6-portbld-freebsd11.0)
> compiled by GNU C version 4.2.1 Compatible FreeBSD Clang 3.8.0 (tags/RELEASE_380/final 262564), GMP version 5.1.3, MPFR version 3.1.4-p1, MPC version 1.0.3, isl version none
> GGC heuristics: --param ggc-min-expand=93 --param ggc-min-heapsize=119509
> ignoring nonexistent directory "/usr/local/lib/gcc6/gcc/armv6-portbld-freebsd11.0/6.2.0/../../../../../armv6-portbld-freebsd11.0/include"
> #include "..." search starts here:
> #include <...> search starts here:
> /usr/local/lib/gcc6/include/c++/
> /usr/local/lib/gcc6/include/c++//armv6-portbld-freebsd11.0
> /usr/local/lib/gcc6/include/c++//backward
> /usr/local/lib/gcc6/gcc/armv6-portbld-freebsd11.0/6.2.0/include
> /usr/local/include
> /usr/local/lib/gcc6/gcc/armv6-portbld-freebsd11.0/6.2.0/include-fixed
> /usr/include
> End of search list.
> GNU C++14 (FreeBSD Ports Collection) version 6.2.0 (armv6-portbld-freebsd11.0)
> compiled by GNU C version 4.2.1 Compatible FreeBSD Clang 3.8.0 (tags/RELEASE_380/final 262564), GMP version 5.1.3, MPFR version 3.1.4-p1, MPC version 1.0.3, isl version none
> GGC heuristics: --param ggc-min-expand=93 --param ggc-min-heapsize=119509
> Compiler executable checksum: 0997b9bc5b083d9cfbb96481fb14adbd
> COLLECT_GCC_OPTIONS='-g' '-v' '-std=c++14' '-Wpedantic' '-Wall' '-O2' '-pthread' '-mcpu=cortex-a7' '-shared-libgcc' '-mtls-dialect=gnu'
> /usr/local/bin/as -v -mcpu=cortex-a7 -mfpu=vfp -meabi=5 -o /tmp//ccx4UQrB.o /tmp//cc0nzkwI.s
> GNU assembler version 2.27 (armv6-portbld-freebsd11.0) using BFD version (GNU Binutils) 2.27
> COMPILER_PATH=/usr/local/libexec/gcc6/gcc/armv6-portbld-freebsd11.0/6.2.0/:/usr/local/libexec/gcc6/gcc/armv6-portbld-freebsd11.0/6.2.0/:/usr/local/libexec/gcc6/gcc/armv6-portbld-freebsd11.0/:/usr/loca
> l/lib/gcc6/gcc/armv6-portbld-freebsd11.0/6.2.0/:/usr/local/lib/gcc6/gcc/armv6-portbld-freebsd11.0/:/usr/local/lib/gcc6/gcc/armv6-portbld-freebsd11.0/6.2.0/../../../../../armv6-portbld-freebsd11.0/bin/
> LIBRARY_PATH=/usr/local/lib/gcc6/gcc/armv6-portbld-freebsd11.0/6.2.0/:/usr/local/lib/gcc6/gcc/armv6-portbld-freebsd11.0/6.2.0/../../../../../armv6-portbld-freebsd11.0/lib/:/usr/local/lib/gcc6/gcc/armv
> 6-portbld-freebsd11.0/6.2.0/../../../:/lib/:/usr/lib/
> COLLECT_GCC_OPTIONS='-g' '-v' '-std=c++14' '-Wpedantic' '-Wall' '-O2' '-pthread' '-mcpu=cortex-a7' '-shared-libgcc' '-mtls-dialect=gnu'
> /usr/local/libexec/gcc6/gcc/armv6-portbld-freebsd11.0/6.2.0/collect2 -plugin /usr/local/libexec/gcc6/gcc/armv6-portbld-freebsd11.0/6.2.0/liblto_plugin.so -plugin-opt=/usr/local/libexec/gcc6/gcc/armv6
> -portbld-freebsd11.0/6.2.0/lto-wrapper -plugin-opt=-fresolution=/tmp//ccD1bSsW.res -plugin-opt=-pass-through=-lgcc_s -plugin-opt=-pass-through=-lgcc -plugin-opt=-pass-through=-lpthread -plugin-opt=-pa
> ss-through=-lc -plugin-opt=-pass-through=-lgcc_s -plugin-opt=-pass-through=-lgcc --eh-frame-hdr -V -dynamic-linker /libexec/ld-elf.so.1 --hash-style=both --enable-new-dtags -X /usr/lib/crt1.o /usr/lib
> /crti.o /usr/local/lib/gcc6/gcc/armv6-portbld-freebsd11.0/6.2.0/crtbegin.o -L/usr/local/lib/gcc6/gcc/armv6-portbld-freebsd11.0/6.2.0 -L/usr/local/lib/gcc6/gcc/armv6-portbld-freebsd11.0/6.2.0/../../../
> ../../armv6-portbld-freebsd11.0/lib -L/usr/local/lib/gcc6/gcc/armv6-portbld-freebsd11.0/6.2.0/../../.. -rpath=/usr/local/lib/gcc6 /tmp//ccx4UQrB.o -lstdc++ -lm -lgcc_s -lgcc -lpthread -lc -lgcc_s -lgc
> c /usr/local/lib/gcc6/gcc/armv6-portbld-freebsd11.0/6.2.0/crtend.o /usr/lib/crtn.o
> GNU ld (GNU Binutils) 2.27
> Supported emulations:
. . .
I end up having to kill -9 gdb as kill and quit each hang.
Just running via ./a.out (no gdb) gets the SIGSEGV but does not hang.
===
Mark Millard
markmi at dsl-only.net
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