Created attachment 41997 [details] preprocessed source thread_local static member templates do not get initialised. Example code: #include <unordered_map> #include <iostream> class A { public: template<typename T> thread_local static std::unordered_map<int,T> m; }; template<typename T> thread_local std::unordered_map<int,T> A::m{}; int main() { // A::m<int> = std::unordered_map<int,int>{}; // workaround std::cout << A::m<int>.bucket_count() << std::endl; // returns zero. A::m<int>.insert({1,2}); // causes SIGPFE (hash modulo bucket_count) } The unordered_map is not initialised and has a bucket count of zero. This leads to a zero division when the hash is taken modulo the bucket count. Without the thread_local or without the template it works fine. A workaround is to initialise the member manually in every thread which uses it (commented line). OS: opensuse Leap 42.3, kernel 4.4.79-19-default x64 CPU: Intel Core i7-4790 $ g++ -o bug -v -save-temps -std=c++14 -Wall -Wextra -pedantic bug.cpp Using built-in specs. COLLECT_GCC=g++ COLLECT_LTO_WRAPPER=/path/to/gcc/svn/lib/gcc/x86_64-pc-linux-gnu/8.0.0/lto-wrapper Target: x86_64-pc-linux-gnu Configured with: ../gcc-svn/configure --prefix=/path/to/gcc/svn --disable-multilib --enable-languages=c,c++,fortran Thread model: posix gcc version 8.0.0 20170817 (experimental) (GCC) COLLECT_GCC_OPTIONS='-o' 'bug' '-v' '-save-temps' '-std=c++14' '-Wall' '-Wextra' '-Wpedantic' '-shared-libgcc' '-mtune=generic' '-march=x86-64' /path/to/gcc/svn/lib/gcc/x86_64-pc-linux-gnu/8.0.0/cc1plus -E -quiet -v -D_GNU_SOURCE bug.cpp -mtune=generic -march=x86-64 -std=c++14 -Wall -Wextra -Wpedantic -fpch-preprocess -o bug.ii ignoring nonexistent directory "/path/to/gcc/svn/lib64/gcc/x86_64-pc-linux-gnu/8.0.0/../../../../x86_64-pc-linux-gnu/include" #include "..." search starts here: #include <...> search starts here: /path/to/gcc/svn/lib64/gcc/x86_64-pc-linux-gnu/8.0.0/../../../../include/c++/8.0.0 /path/to/gcc/svn/lib64/gcc/x86_64-pc-linux-gnu/8.0.0/../../../../include/c++/8.0.0/x86_64-pc-linux-gnu /path/to/gcc/svn/lib64/gcc/x86_64-pc-linux-gnu/8.0.0/../../../../include/c++/8.0.0/backward /path/to/gcc/svn/lib64/gcc/x86_64-pc-linux-gnu/8.0.0/include /usr/local/include /path/to/gcc/svn/include /path/to/gcc/svn/lib64/gcc/x86_64-pc-linux-gnu/8.0.0/include-fixed /usr/include End of search list. COLLECT_GCC_OPTIONS='-o' 'bug' '-v' '-save-temps' '-std=c++14' '-Wall' '-Wextra' '-Wpedantic' '-shared-libgcc' '-mtune=generic' '-march=x86-64' /path/to/gcc/svn/lib/gcc/x86_64-pc-linux-gnu/8.0.0/cc1plus -fpreprocessed bug.ii -quiet -dumpbase bug.cpp -mtune=generic -march=x86-64 -auxbase bug -Wall -Wextra -Wpedantic -std=c++14 -version -o bug.s GNU C++14 (GCC) version 8.0.0 20170817 (experimental) (x86_64-pc-linux-gnu) compiled by GNU C version 8.0.0 20170817 (experimental), GMP version 6.1.2, MPFR version 3.1.5, MPC version 1.0.3, isl version none GGC heuristics: --param ggc-min-expand=30 --param ggc-min-heapsize=4096 GNU C++14 (GCC) version 8.0.0 20170817 (experimental) (x86_64-pc-linux-gnu) compiled by GNU C version 8.0.0 20170817 (experimental), GMP version 6.1.2, MPFR version 3.1.5, MPC version 1.0.3, isl version none GGC heuristics: --param ggc-min-expand=30 --param ggc-min-heapsize=4096 Compiler executable checksum: 7aa65dd64f7a61cf2867713db376431f COLLECT_GCC_OPTIONS='-o' 'bug' '-v' '-save-temps' '-std=c++14' '-Wall' '-Wextra' '-Wpedantic' '-shared-libgcc' '-mtune=generic' '-march=x86-64' as -v --64 -o bug.o bug.s GNU assembler version 2.26.1 (x86_64-suse-linux) using BFD version (GNU Binutils; openSUSE Leap 42.3) 2.26.1 COMPILER_PATH=/path/to/gcc/svn/lib/gcc/x86_64-pc-linux-gnu/8.0.0/:/path/to/gcc/svn/lib/gcc/x86_64-pc-linux-gnu/8.0.0/:/path/to/gcc/svn/lib/gcc/x86_64-pc-linux-gnu/:/path/to/gcc/svn/lib64/gcc/x86_64-pc-linux-gnu/8.0.0/:/path/to/gcc/svn/lib64/gcc/x86_64-pc-linux-gnu/ LIBRARY_PATH=/path/to/gcc/svn/lib64/gcc/x86_64-pc-linux-gnu/8.0.0/:/path/to/gcc/svn/lib64/gcc/x86_64-pc-linux-gnu/8.0.0/../../../../lib64/:/lib/../lib64/:/usr/lib/../lib64/:./:/path/to/gcc/svn/lib64/gcc/x86_64-pc-linux-gnu/8.0.0/../../../:/lib/:/usr/lib/ COLLECT_GCC_OPTIONS='-o' 'bug' '-v' '-save-temps' '-std=c++14' '-Wall' '-Wextra' '-Wpedantic' '-shared-libgcc' '-mtune=generic' '-march=x86-64' /path/to/gcc/svn/lib/gcc/x86_64-pc-linux-gnu/8.0.0/collect2 -plugin /path/to/gcc/svn/lib/gcc/x86_64-pc-linux-gnu/8.0.0/liblto_plugin.so -plugin-opt=/path/to/gcc/svn/lib/gcc/x86_64-pc-linux-gnu/8.0.0/lto-wrapper -plugin-opt=-fresolution=bug.res -plugin-opt=-pass-through=-lgcc_s -plugin-opt=-pass-through=-lgcc -plugin-opt=-pass-through=-lc -plugin-opt=-pass-through=-lgcc_s -plugin-opt=-pass-through=-lgcc --eh-frame-hdr -m elf_x86_64 -dynamic-linker /lib64/ld-linux-x86-64.so.2 -o bug /usr/lib/../lib64/crt1.o /usr/lib/../lib64/crti.o /path/to/gcc/svn/lib64/gcc/x86_64-pc-linux-gnu/8.0.0/crtbegin.o -L/path/to/gcc/svn/lib64/gcc/x86_64-pc-linux-gnu/8.0.0 -L/path/to/gcc/svn/lib64/gcc/x86_64-pc-linux-gnu/8.0.0/../../../../lib64 -L/lib/../lib64 -L/usr/lib/../lib64 -L. -L/path/to/gcc/svn/lib64/gcc/x86_64-pc-linux-gnu/8.0.0/../../.. bug.o -lstdc++ -lm -lgcc_s -lgcc -lc -lgcc_s -lgcc /path/to/gcc/svn/lib64/gcc/x86_64-pc-linux-gnu/8.0.0/crtend.o /usr/lib/../lib64/crtn.o COLLECT_GCC_OPTIONS='-o' 'bug' '-v' '-save-temps' '-std=c++14' '-Wall' '-Wextra' '-Wpedantic' '-shared-libgcc' '-mtune=generic' '-march=x86-64' $ ./bug 0 Floating point exception (core dumped) (also confirmed with gcc 7.1.1 and gcc 5.2.0)
works with clang++
This bug still seems to exist in the current 9.0 HEAD. Note also that another possible work-around might be to wrap the thread_local member in an accessor function, along the lines of class A { public: template<typename T> std::unordered_map<int,T> & get_m () { thread_local static std::unordered_map<int,T> m; return m; } };
I played around a bit with gcc, and it looks like the example can be made to work via the following diff: --------------------------------------- diff --git a/gcc/cp/semantics.c b/gcc/cp/semantics.c index 639b00264d8..f6b10174f1b 100644 --- a/gcc/cp/semantics.c +++ b/gcc/cp/semantics.c @@ -3898,6 +3898,8 @@ finish_id_expression_1 (tree id_expression, decl = finish_template_variable (decl); mark_used (decl); decl = convert_from_reference (decl); + if (tree wrap = maybe_get_tls_wrapper_call (decl)) + decl = wrap; } else if (concept_check_p (decl)) { --------------------------------------- Not sure if this makes sense, though, in the greater scheme of things. So I'll just leave that here FYI.
Reduced testcase: extern "C" void abort(void); struct tt { int *tt1 = new int{1}; int bucket_count() const {return *tt1;} }; struct A { template<typename T> thread_local static tt m; }; template<typename T> thread_local tt A::m{}; int main() { if ( A::m<int>.bucket_count() != 1) abort(); return 0; }
we are observing this with gcc 10.3.0