toolchain/53810: C++ exception does not work on m68k when libstdc++ is dynamicaly linked

[rokuyama%rk.phys.keio.ac.jp@localhost]

>Number:         53810
>Category:       toolchain
>Synopsis:       C++ exception does not work on m68k when libstdc++ is dynamicaly linked
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    toolchain-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue Dec 25 12:20:00 +0000 2018
>Originator:     Rin Okuyama
>Release:        8.99.29
>Organization:
Department of Physics, Meiji University
>Environment:
NetBSD a1200 8.99.29 NetBSD 8.99.29 (A1200) #0: Tue Dec 25 18:50:38 JST 2018  rin@latipes:/var/build/src/sys/arch/amiga/compile/A1200 amiga
>Description:
Throwing C++ exceptions fails on m68k:

---
% cat exception.cpp
#include <stdio.h>

class Usage{};

int main(int argc, char *argv[]) {
	try {
		if (argc != 2)
			throw Usage();
		printf("%s\n", argv[1]);
		return 0;
	}
	catch (const Usage&) {
		printf("usage: %s str\n", argv[0]);
		return 1;
	}
}
% g++ exception.cpp
% ./a.out
terminate called after throwing an instance of 'Usage'
zsh: abort (core dumped)  ./a.out
---

This code works fine if libstdc++ is statically linked:

---
% g++ -static exception.cpp
% ./a.out
usage: ./a.out str
---

This does not mean that it does not work with dynamically-linked
binaries; It also works when only libstdc++ is statically linked:

---
% ld -dynamic-linker /usr/libexec/ld.elf_so /usr/lib/crt0.o /usr/lib/crti.o /usr/lib/crtbegin.o exception.o /usr/lib/libstdc++.a -lm -lgcc -lc -lgcc /usr/lib/crtend.o /usr/lib/crtn.o
% ldd a.out
a.out:
        -lm.0 => /usr/lib/libm.so.0
        -lc.12 => /usr/lib/libc.so.12
% ./a.out
usage: ./a.out str
---

It should be a root cause for the following PRs:

toolchain/53684: atf-run fails on m68k
toolchain/53685: gdb fails on m68k

Actually, both gdb and atf-run work normally when they are statically
linked.

Note that this problem does not occur with GCC 5.5 from gcc.old in
NetBSD-current as of 20180801.
>How-To-Repeat:
Described above.
>Fix:
Not known yet.