cxx.features.modules crash with freestanding gcc

[wroyca]

Using freestanding gcc causes a crash if we enable cxx.features.modules

> /home/wroy/gcc/bin/x86_64-elf-g++ --version                                                     
x86_64-elf-g++ (GCC) 13.0.0 20221018 (experimental)
Copyright (C) 2022 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

> b config.cxx="/home/wroy/gcc/bin/x86_64-elf-g++"
libbuild2/cc/guess.cxx:3572: void build2::cc::guess_std_importable_headers(const compiler_info&, const build2::dir_paths&, importable_headers&): Assertion `p != nullptr' failed.

> gdb b core.b.1000.7b8d36aba88a4fbb90d07f1f188eddda.43115.1666200631000000
Core was generated by `b config.cxx=/home/wroy/gcc/bin/x86_64-elf-g++'.
Program terminated with signal SIGABRT, Aborted.

[Current thread is 1 (Thread 0x7fbb3bc85140 (LWP 43115))]
#0  0x00007fbb3bd20ccc in __pthread_kill_implementation () from /lib64/libc.so.6
No symbol table info available.
#1  0x00007fbb3bcd0aa6 in raise () from /lib64/libc.so.6
No symbol table info available.
#2  0x00007fbb3bcba7fc in abort () from /lib64/libc.so.6
No symbol table info available.
#3  0x00007fbb3bcba71b in __assert_fail_base.cold () from /lib64/libc.so.6
No symbol table info available.
#4  0x00007fbb3bcc9656 in __assert_fail () from /lib64/libc.so.6
No symbol table info available.
#5  0x00007fbb3c372d19 in build2::cc::guess_std_importable_headers(build2::cc::compiler_info const&, std::vector<butl::basic_path<char, butl::dir_path_kind<char> >, std::allocator<butl::basic_path<char, butl::dir_path_kind<char> > > > const&, build2::cc::importable_headers&) () from /usr/local/lib/build2/libbuild2-cc-0.16.0-a.0.18394bc05dc4-0.16.0-a.0.18394bc05dc4.so
No symbol table info available.
#6  0x00007fbb3c323e4e in build2::cc::module::init(build2::scope&, build2::location const&, build2::variable_map const&, build2::cc::compiler_info const&) ()
   from /usr/local/lib/build2/libbuild2-cc-0.16.0-a.0.18394bc05dc4-0.16.0-a.0.18394bc05dc4.so
No symbol table info available.
#7  0x00007fbb3c3e9f30 in build2::cxx::init(build2::scope&, build2::scope&, build2::location const&, bool, bool, build2::module_init_extra&) () 
   from /usr/local/lib/build2/libbuild2-cc-0.16.0-a.0.18394bc05dc4-0.16.0-a.0.18394bc05dc4.so
#8  0x00007fbb3c73aa96 in build2::init_module(build2::scope&, build2::scope&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, build2::location const&, bool, build2::variable_map const&) () from /usr/local/lib/build2/libbuild2-0.16.0-a.0.18394bc05dc4.so
No symbol table info available.
#9  0x00007fbb3c790f26 in build2::parser::parse_using(build2::token&, build2::token_type&) () from /usr/local/lib/build2/libbuild2-0.16.0-a.0.18394bc05dc4.so
No symbol table info available.
#10 0x00007fbb3c7a2d37 in build2::parser::parse_clause(build2::token&, build2::token_type&, bool) () from /usr/local/lib/build2/libbuild2-0.16.0-a.0.18394bc05dc4.so
No symbol table info available.
#11 0x00007fbb3c7a7a6e in build2::parser::parse_buildfile(build2::lexer&, build2::scope*, build2::scope&, build2::target*, build2::prerequisite*) ()
   from /usr/local/lib/build2/libbuild2-0.16.0-a.0.18394bc05dc4.so
No symbol table info available.
#12 0x00007fbb3c656c08 in build2::source(build2::parser&, build2::scope&, build2::scope&, build2::lexer&) () from /usr/local/lib/build2/libbuild2-0.16.0-a.0.18394bc05dc4.so
No symbol table info available.
#13 0x00007fbb3c6617f7 in build2::source(build2::parser&, build2::scope&, build2::scope&, butl::basic_path<char, butl::any_path_kind<char> > const&) ()
   from /usr/local/lib/build2/libbuild2-0.16.0-a.0.18394bc05dc4.so
No symbol table info available.
#14 0x00007fbb3c661b49 in build2::source_once(build2::parser&, build2::scope&, build2::scope&, butl::basic_path<char, butl::any_path_kind<char> > const&, build2::scope&) ()
   from /usr/local/lib/build2/libbuild2-0.16.0-a.0.18394bc05dc4.so
No symbol table info available.
#15 0x00007fbb3c663288 in build2::load_root(build2::scope&, std::function<void (build2::parser&)> const&, std::function<void (build2::parser&)> const&) ()
   from /usr/local/lib/build2/libbuild2-0.16.0-a.0.18394bc05dc4.so
No symbol table info available.
#16 0x00007fbb3c6afd71 in build2::perform_load(butl::small_vector<build2::value, 1ul> const&, build2::scope&, butl::basic_path<char, butl::any_path_kind<char> > const&, butl::basic_path<char, butl::dir_path_kind<char> > const&, butl::basic_path<char, butl::dir_path_kind<char> > const&, build2::location const&) ()
   from /usr/local/lib/build2/libbuild2-0.16.0-a.0.18394bc05dc4.so
No symbol table info available.
#17 0x0000000000412f3c in build2::main(int, char**) ()
No symbol table info available.
#18 0x00007fbb3bcbb510 in __libc_start_call_main () from /lib64/libc.so.6
No symbol table info available.
#19 0x00007fbb3bcbb5c9 in __libc_start_main_impl () from /lib64/libc.so.6
No symbol table info available.
#20 0x0000000000418495 in _start ()
No symbol table info available.

[boris-kolpackov]

Hm, interesting. Do you have any of the headers from this list: https://github.com/build2/build2/blob/master/libbuild2/cc/guess.cxx#L3426 Perhaps <version>?

[wroyca]

Hm, interesting. Do you have any of the headers from this list: https://github.com/build2/build2/blob/master/libbuild2/cc/guess.cxx#L3426 Perhaps <version>?

I do not. :)
It is reproducible with an "empty" source file, something like:

export module foo;

export auto main ([[maybe_unused]] const int argc, [[maybe_unused]] char *argv[]) {
}

[boris-kolpackov]

It doesn't seem not having any std headers in freestanding is conforming: https://eel.is/c++draft/compliance Though I see <version> is not on that list. In any case, we now use <initializer_list> to discover the std header directory but also handle the case where even that is not present.

[boris-kolpackov]

The fix is available in the latest staged toolchain.

[wroyca]

It doesn't seem not having any std headers in freestanding is conforming:

Oops, we misunderstood each others, the compiler has the usual headers available in freestanding. Thanks for the quick fix!