NetBSD Problem Report #53810

From www@NetBSD.org  Tue Dec 25 12:17:20 2018
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Message-Id: <20181225121718.B70AE7A1E3@mollari.NetBSD.org>
Date: Tue, 25 Dec 2018 12:17:18 +0000 (UTC)
From: rokuyama@rk.phys.keio.ac.jp
Reply-To: rokuyama@rk.phys.keio.ac.jp
To: gnats-bugs@NetBSD.org
Subject: C++ exception does not work on m68k when libstdc++ is dynamicaly linked
X-Send-Pr-Version: www-1.0

>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:          closed
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue Dec 25 12:20:00 +0000 2018
>Closed-Date:    Thu Feb 21 10:50:25 +0000 2019
>Last-Modified:  Thu Feb 21 10:50:25 +0000 2019
>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.

>Release-Note:

>Audit-Trail:
From: matthew green <mrg@eterna.com.au>
To: gnats-bugs@NetBSD.org
Cc: toolchain-manager@netbsd.org, gnats-admin@netbsd.org,
    netbsd-bugs@netbsd.org
Subject: re: toolchain/53810: C++ exception does not work on m68k when libstdc++ is dynamicaly linked
Date: Sat, 29 Dec 2018 08:15:21 +1100

 Rin Okuyama writes:
 > On archs other than m68k, libstdc++.so and C++ binaries depend on
 > libgcc_s.so. On m68k, this is not the case: -shared-libgcc is
 > observed in "g++ -v", but only -lgcc (not -lgcc_s) is passed to ld:
 [ ..]
 > Can I commit the patch?

 go for it.  thanks for a good diagnosis!


 .mrg.

From: "Rin Okuyama" <rin@netbsd.org>
To: gnats-bugs@gnats.NetBSD.org
Cc: 
Subject: PR/53810 CVS commit: src/external/gpl3
Date: Fri, 28 Dec 2018 21:30:20 +0000

 Module Name:	src
 Committed By:	rin
 Date:		Fri Dec 28 21:30:20 UTC 2018

 Modified Files:
 	src/external/gpl3/gcc.old/dist/gcc/config/m68k: netbsd-elf.h
 	src/external/gpl3/gcc/dist/gcc/config/m68k: netbsd-elf.h

 Log Message:
 PR toolchain/53810
 PR toolchain/53684
 PR toolchain/53685

 No one defines TARGET_DEFAULT_CPU anymore. Use ENABLE_SHARED_LIBGCC
 instead to determine whether GCC is configured for m68k or m68000.
 This fixes C++ binaries on m68k, that require libgcc_s.

 OK mrg


 To generate a diff of this commit:
 cvs rdiff -u -r1.6 -r1.7 \
     src/external/gpl3/gcc.old/dist/gcc/config/m68k/netbsd-elf.h
 cvs rdiff -u -r1.12 -r1.13 \
     src/external/gpl3/gcc/dist/gcc/config/m68k/netbsd-elf.h

 Please note that diffs are not public domain; they are subject to the
 copyright notices on the relevant files.

From: Rin Okuyama <rokuyama@rk.phys.keio.ac.jp>
To: matthew green <mrg@eterna.com.au>, gnats-bugs@NetBSD.org
Cc: toolchain-manager@netbsd.org, gnats-admin@netbsd.org,
 netbsd-bugs@netbsd.org
Subject: Re: toolchain/53810: C++ exception does not work on m68k when
 libstdc++ is dynamicaly linked
Date: Sat, 29 Dec 2018 06:38:29 +0900

 On 2018/12/29 6:15, matthew green wrote:
 > Rin Okuyama writes:
 >> On archs other than m68k, libstdc++.so and C++ binaries depend on
 >> libgcc_s.so. On m68k, this is not the case: -shared-libgcc is
 >> observed in "g++ -v", but only -lgcc (not -lgcc_s) is passed to ld:
 > [ ..]
 >> Can I commit the patch?
 > 
 > go for it.  thanks for a good diagnosis!

 Committed. Thank you for your quick response!

 rin

 PS
 My previous message did not appear on GNATS for some reason.
 I added the link for the record:
 http://mail-index.netbsd.org/netbsd-bugs/2018/12/28/msg060157.html

From: David Holland <dholland-bugs@netbsd.org>
To: gnats-bugs@netbsd.org
Cc: 
Subject: Re: toolchain/53810: C++ exception does not work on m68k when
 libstdc++ is dynamicaly linked
Date: Wed, 9 Jan 2019 19:15:59 +0000

 (not sent to gnats)

    ------

 From: Rin Okuyama <rokuyama@rk.phys.keio.ac.jp>
 To: toolchain-manager@netbsd.org, gnats-admin@netbsd.org,
 	netbsd-bugs@netbsd.org
 Subject: Re: toolchain/53810: C++ exception does not work on m68k when
 	libstdc++ is dynamicaly linked
 Date: Sat, 29 Dec 2018 06:09:03 +0900

 On archs other than m68k, libstdc++.so and C++ binaries depend on
 libgcc_s.so. On m68k, this is not the case: -shared-libgcc is
 observed in "g++ -v", but only -lgcc (not -lgcc_s) is passed to ld:

   % uname -p
   m68k
   % g++ -v hello.c
   ...
    ld ... /tmp/cc8plluA.o -lstdc++ -lm -lgcc -lc -lgcc /usr/lib/crtend.o ...
    COLLECT_GCC_OPTIONS='-v' '-shared-libgcc' '-mcpu=68020'
   % ldd a.out
   a.out:
 	-lstdc++.8 => /usr/lib/libstdc++.so.8
 	-lm.0 => /usr/lib/libm.so.0
 	-lc.12 => /usr/lib/libc.so.12

 What the difference between m68k and others? I found an answer in
 external/gpl3/gcc/dist/gcc/config/m68k/netbsd-elf.h:

     81  /* NetBSD/sun2 does not support shlibs, avoid using libgcc_pic.  */
     82  #if TARGET_DEFAULT_CPU == 0
     83  #undef REAL_LIBGCC_SPEC
     84  #define REAL_LIBGCC_SPEC        "-lgcc"
     85  #endif

 This hack for m68000 does not work anymore since no one in source
 tree defines TARGET_DEFAULT_CPU. Therefore, even for m68k machines,
 -lgcc is used when -lgcc_s is more appropriate.

 I've modified the hack as follows:

     81  /* NetBSD/sun2 does not support shlibs, avoid using libgcc_pic.  */
     82  #ifndef ENABLE_SHARED_LIBGCC
     83  #undef REAL_LIBGCC_SPEC
     84  #define REAL_LIBGCC_SPEC        "-lgcc"
     85  #endif

 Then, C++ applications on m68k get working again. Also, sun2 seems
 no more broken than before (-current kernel does not boot on TME
 regardless of my patch. Userland built with the patch works to
 some extent on 8.0 kernel).

 Can I commit the patch?

 Thanks,
 rin

 Index: external/gpl3/gcc.old/dist/gcc/config/m68k/netbsd-elf.h
 ===================================================================
 RCS file: /home/netbsd/src/external/gpl3/gcc.old/dist/gcc/config/m68k/netbsd-elf.h,v
 retrieving revision 1.6
 diff -p -u -r1.6 netbsd-elf.h
 --- external/gpl3/gcc.old/dist/gcc/config/m68k/netbsd-elf.h	2 Aug 2018 00:02:57 -0000	1.6
 +++ external/gpl3/gcc.old/dist/gcc/config/m68k/netbsd-elf.h	28 Dec 2018 11:29:00 -0000
 @@ -79,7 +79,7 @@ along with GCC; see the file COPYING3.
  #define LINK_SPEC NETBSD_LINK_SPEC_ELF

  /* NetBSD/sun2 does not support shlibs, avoid using libgcc_pic.  */
 -#if TARGET_DEFAULT_CPU == 0
 +#ifndef ENABLE_SHARED_LIBGCC
  #undef REAL_LIBGCC_SPEC
  #define REAL_LIBGCC_SPEC	"-lgcc"
  #endif
 Index: external/gpl3/gcc/dist/gcc/config/m68k/netbsd-elf.h
 ===================================================================
 RCS file: /home/netbsd/src/external/gpl3/gcc/dist/gcc/config/m68k/netbsd-elf.h,v
 retrieving revision 1.12
 diff -p -u -r1.12 netbsd-elf.h
 --- external/gpl3/gcc/dist/gcc/config/m68k/netbsd-elf.h	2 Feb 2018 03:41:05 -0000	1.12
 +++ external/gpl3/gcc/dist/gcc/config/m68k/netbsd-elf.h	28 Dec 2018 11:29:40 -0000
 @@ -79,7 +79,7 @@ along with GCC; see the file COPYING3.
  #define LINK_SPEC NETBSD_LINK_SPEC_ELF

  /* NetBSD/sun2 does not support shlibs, avoid using libgcc_pic.  */
 -#if TARGET_DEFAULT_CPU == 0
 +#ifndef ENABLE_SHARED_LIBGCC
  #undef REAL_LIBGCC_SPEC
  #define REAL_LIBGCC_SPEC	"-lgcc"
  #endif

State-Changed-From-To: open->closed
State-Changed-By: rin@NetBSD.org
State-Changed-When: Thu, 21 Feb 2019 10:50:25 +0000
State-Changed-Why:
fixed while ago


>Unformatted:

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