NetBSD Problem Report #60875

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	for <gnats-bugs@gnats.NetBSD.org>; Wed, 14 Oct 2026 10:04:20 +0000 (UTC)
Message-Id: <20261014100418.D3D6D1A923C@mollari.NetBSD.org>
Date: Wed, 14 Oct 2026 10:04:18 +0000 (UTC)
From: rokuyama.rk@gmail.com
Reply-To: rokuyama.rk@gmail.com
To: gnats-bugs@NetBSD.org
Subject: open-simh: miscompiled by GCC on NetBSD/amd64
X-Send-Pr-Version: www-1.0
X-From4GNATS: "rokuyama.rk@gmail.com via gnats" <gnats-admin@NetBSD.org>

>Number:         60875
>Category:       pkg
>Synopsis:       open-simh: miscompiled by GCC on NetBSD/amd64
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    rhialto
>State:          analyzed
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Oct 14 10:05:00 +0000 2026
>Closed-Date:    
>Last-Modified:  Thu Oct 15 12:00:02 +0000 2026
>Originator:     Rin Okuyama
>Release:        11.99.9 and 2026Q3
>Organization:
Internet Initiative Japan Inc.
>Environment:
NetBSD sakaizumii.local 11.99.9 NetBSD 11.99.9 (AMD64_NET_MPSAFE) #2: Sat Oct 10 17:06:17 JST 2026  rin@sakaizumii.local:/home/rin/src/sys/arch/amd64/compile/AMD64_NET_MPSAFE amd64
>Description:
For open-simh-4.1.0.20260413nb2 on NetBSD/amd64-current, "normal
system test 31" fails:

```
% simh-vax NetBSD-11.99.9-vax-live.boot

MicroVAX 3900 simulator Open SIMH V4.1-0 Current        simh git commit id: 7994e0a7        Build: Unsupported=include+lib
/old/home/rin/vax/NetBSD-11.99.9-vax-live.boot-9> attach xq tap:tap0
%SIM-INFO: Eth: opened OS device tap0


KA655X-B V5.3, VMB 2.7
Performing normal system tests.
40..39..38..37..36..35..34..33..32..31..

?53 2 07 FF 00 0000

P1=00000002  P2=00000028  P3=00000000  P4=00D40077  P5=00000000
P6=FFFFFFFF  P7=00000000  P8=00000000  P9=00000000 P10=20051CE0
r0=A380D3C6  r1=20140110  r2=A380D3C7  r3=00000000  r4=A380D3D1
r5=2004E8F9  r6=000F4240  r7=80000011  r8=00000000 ERF=80000000
30..29..28..27..26..25..
24..23..22..21..20..19..18..17..16..15..14..13..12..11..10..09..
08..07..06..05..04..03..
Normal operation not possible.

>>>
```

I'm using this config file:

```
load -r ka655x.bin
set cpu 256m
set cpu idle=netbsd
set rq0 ra92
at rq0 NetBSD-11.99.9-vax-live.img
attach xq tap:tap0
boot cpu
```

and ka655x.bin acquired from here:
https://github.com/simh/simh/blob/master/VAX/ka655x.bin

This failure happens with GCC 10.5 (from netbsd-10 branch), 12.5,
and 14.4.

In order to work around, compile open-simh with -O3 or -O1 on
NetBSD/amd64. I've confirmed that full ATF run of NetBSD/vax on
-O3 compiled open-simh successfully completes with GCC 10.5, 12.5,
and 14.4.

I haven't tested emulators other than simh-vax on the other hand.
>How-To-Repeat:
Described above.
>Fix:
diff --git a/emulators/open-simh/Makefile b/emulators/open-simh/Makefile
index 857d0db21ced..3f18d6ed4f38 100644
--- a/emulators/open-simh/Makefile
+++ b/emulators/open-simh/Makefile
@@ -2,7 +2,7 @@

 DISTNAME=	open-simh-4.1.0
 PKGNAME=	open-simh-4.1.0.20260413
-PKGREVISION=	2
+PKGREVISION=	3
 CATEGORIES=	emulators
 MASTER_SITES=	${MASTER_SITE_GITHUB:=open-simh/}
 GITHUB_PROJECT=	simh
diff --git a/emulators/open-simh/hacks.mk b/emulators/open-simh/hacks.mk
new file mode 100644
index 000000000000..b972dc59cfe2
--- /dev/null
+++ b/emulators/open-simh/hacks.mk
@@ -0,0 +1,14 @@
+# $NetBSD$
+
+.if !defined(OPEN_SIMH_HACKS_MK)
+OPEN_SIMH_HACKS_MK=	defined
+
+.include "../../mk/compiler.mk"
+
+# For simh-vax, "normal system tests 31" fails.
+.if ${MACHINE_PLATFORM:MNetBSD-*-x86_64} && ${CC_VERSION:Mgcc-*}
+PKG_HACKS+=		optimisation
+BUILDLINK_TRANSFORM+=	opt:-O2:-O3
+.endif
+
+.endif	# OPEN_SIMH_HACKS_MK

>Release-Note:

>Audit-Trail:

Responsible-Changed-From-To: pkg-manager->rhialto
Responsible-Changed-By: rin@NetBSD.org
Responsible-Changed-When: Wed, 14 Oct 2026 10:07:15 +0000
Responsible-Changed-Why:
Over to maintainer; can you please take a look?


From: Rhialto <rhialto@falu.nl>
To: gnats-bugs@netbsd.org
Cc: rhialto@netbsd.org, pkg-manager@netbsd.org, pkgsrc-bugs@netbsd.org,
	gnats-admin@netbsd.org, rin@NetBSD.org, rokuyama.rk@gmail.com
Subject: Re: pkg/60875 (open-simh: miscompiled by GCC on NetBSD/amd64)
Date: Wed, 14 Oct 2026 21:50:46 +0200

 I tried to reproduce this in my own environment (NetBSD 11.0 amd64 with
 gcc 12.5.0 from base) but did not succeed. (I attached a different disk
 image which I had at hand, but that should make no difference, since it
 is never read)

 This does not prove much, because the upstream code relies on UB
 (undefined behavior) especially in the VAX code. The most obvious one is
 that it assumes that overflow of signed integers works the same as with
 unsigned integers. They are relucant to change the code: a long time ago
 it has been validated with proprietary DEC instruction set validation
 tests, and those are no longer available.

 Due to the UB, there is a large number of compiler options to try to
 make it work anyway. It could be that in your compilation some of these
 are missing (due to a different environment). If this is the case,
 fixing that may fix the issue.

 I also tried
 https://cdn.netbsd.org/pub/pkgsrc/packages/NetBSD/x86_64/11.0_2026Q3/All/op=
 en-simh-4.1.0.20260413nb2.tgz
 and it did not reproduce the issue either.

 I have compile commands like this:

 gcc -std=3Dgnu99 -U__STRICT_ANSI__  -fno-strict-overflow
     -finline-functions -fpredictive-commoning -fipa-cp-clone
     -fgcse-after-reload -fno-unsafe-loop-optimizations -O2 -DNDEBUG=3D1
     -finline-functions -fgcse-after-reload -fpredictive-commoning
     -fipa-cp-clone -fno-unsafe-loop-optimizations -fno-strict-overflow
     -DSIM_BUILD=3DUnsupported=3Dinclude+lib  -DSIM_COMPILER=3D"GCC Version:
     12.5.0" -DSIM_BUILD_TOOL=3Dsimh-makefile -I .  -D_GNU_SOURCE -DHAVE_PCR=
 E_H
     -DHAVE_SEMAPHORE -DHAVE_SYS_IOCTL -DSIM_HAVE_DLOPEN=3Dso -DHAVE_EDITLINE
     -DHAVE_UTIME -DHAVE_LIBPNG -DHAVE_ZLIB -DHAVE_GLOB -DHAVE_SHM_OPEN
     ./VAX/vax_cpu.c ./VAX/vax_cpu1.c ./VAX/vax_fpa.c ./VAX/vax_io.c
     ./VAX/vax_cis.c ./VAX/vax_octa.c  ./VAX/vax_cmode.c./VAX/vax_mmu.c
     ./VAX/vax_stddev.c ./VAX/vax_sysdev.c ./VAX/vax_sys.c  ./VAX/vax_syscm.c
     ./VAX/vax_syslist.c ./VAX/vax_vc.c ./VAX/vax_lk.c ./VAX/vax_vs.c
     ./VAX/vax_2681.c ./PDP11/pdp11_rl.c ./PDP11/pdp11_rq.c
     ./PDP11/pdp11_ts.c ./PDP11/pdp11_dz.c ./PDP11/pdp11_lp.c
     ./PDP11/pdp11_tq.c ./PDP11/pdp11_xq.c ./PDP11/pdp11_vh.c
     ./PDP11/pdp11_cr.c ./PDP11/pdp11_td.c ./PDP11/pdp11_io_lib.c
     ./PDP11/pdp11_dup.c ./scp.c ./sim_console.c ./sim_fio.c ./sim_timer.c
     ./sim_sock.c ./sim_tmxr.c ./sim_ether.c ./sim_tape.c ./sim_disk.c
     ./sim_serial.c ./sim_video.c ./sim_imd.c ./sim_card.c -DVM_VAX
     -DUSE_INT64 -DUSE_ADDR64 -DUSE_SIM_VIDEO -I ./VAX -I ./PDP11
     -DHAVE_PCAP_NETWORK -I/usr/include/pcap/ -DBPF_CONST_STRING
     -DUSE_NETWORK -DHAVE_VDE_NETWORK -DHAVE_TAP_NETWORK -DHAVE_BSDTUNTAP
     -Islirp -Islirp_glue -Islirp_glue/qemu -DHAVE_SLIRP_NETWORK
     -DUSE_SIMH_SLIRP_DEBUG slirp/*.c slirp_glue/*.c -DHAVE_LIBSDL
     -DUSE_SIM_VIDEO `sdl2-config --cflags` `sdl2-config --libs`
     -DUSE_READER_THREAD -DSIM_ASYNCH_IO -o BIN/vax  -Wl,-zrelro
     -L/usr/pkg/lib -Wl,-R/usr/pkg/lib -L/usr/X11R7/lib -Wl,-R/usr/X11R7/lib
     -L/usr/lib -Wl,-R/usr/lib -lm -lrt -lpthread -lpcre -L/usr/pkg/lib/
     -ledit -ltermcap -lpng16 -lz -lpcap -lvdeplug -Wl,-R,/usr/pkg/lib/
     -L/usr/pkg/lib/

 (You can ignore references to VDE or vdeplug; this refers to wip/vde2)

 Aside: the config line "load -r ka655x.bin" should not be needed, since
 the same file is built-in. Simh will say "%SIM-INFO: Loading boot code
 =66rom internal ka655x.bin"

 It may be that adding -Wstrict-overflow=3D5 shows some useful diagnostic.

 If this does not show any missing options, I have no objection if you
 commit the changes you propose.

 -Olaf.
 --=20
 ___ Olaf 'Rhialto' Seibert                            <rhialto/at/falu.nl>
 \X/ There is no AI. There is just someone else's work.           --I. Rose

State-Changed-From-To: open->analyzed
State-Changed-By: rin@NetBSD.org
State-Changed-When: Thu, 15 Oct 2026 11:58:46 +0000
State-Changed-Why:
I couldn't reproduce the problem with official buit package of
2026Q3 for netbsd-11. So, this may be my local settings...


From: Rin Okuyama <rokuyama.rk@gmail.com>
To: Rhialto <rhialto@falu.nl>, gnats-bugs@netbsd.org
Cc: rhialto@netbsd.org, pkg-manager@netbsd.org, pkgsrc-bugs@netbsd.org,
 gnats-admin@netbsd.org
Subject: Re: pkg/60875 (open-simh: miscompiled by GCC on NetBSD/amd64)
Date: Thu, 15 Oct 2026 20:57:17 +0900

 Thank you very much for kind explanation!

 On 2026/10/15 4:50, Rhialto wrote:
 > I tried to reproduce this in my own environment (NetBSD 11.0 amd64 with
 > gcc 12.5.0 from base) but did not succeed. (I attached a different disk
 > image which I had at hand, but that should make no difference, since it
 > is never read)
 > 
 > This does not prove much, because the upstream code relies on UB
 > (undefined behavior) especially in the VAX code. The most obvious one is
 > that it assumes that overflow of signed integers works the same as with
 > unsigned integers. They are relucant to change the code: a long time ago
 > it has been validated with proprietary DEC instruction set validation
 > tests, and those are no longer available.
 > 
 > Due to the UB, there is a large number of compiler options to try to
 > make it work anyway. It could be that in your compilation some of these
 > are missing (due to a different environment). If this is the case,
 > fixing that may fix the issue.
 > 
 > I also tried
 > https://cdn.netbsd.org/pub/pkgsrc/packages/NetBSD/x86_64/11.0_2026Q3/All/open-simh-4.1.0.20260413nb2.tgz
 > and it did not reproduce the issue either.

 I tried that package, and I also couldn't reproduce the problem.
 So, this may be my local settings, but I haven't figured out what
 causes the problem...

 > I have compile commands like this:
 > 
 > gcc -std=gnu99 -U__STRICT_ANSI__  -fno-strict-overflow
 >      -finline-functions -fpredictive-commoning -fipa-cp-clone
 >      -fgcse-after-reload -fno-unsafe-loop-optimizations -O2 -DNDEBUG=1
 >      -finline-functions -fgcse-after-reload -fpredictive-commoning
 >      -fipa-cp-clone -fno-unsafe-loop-optimizations -fno-strict-overflow
 >      -DSIM_BUILD=Unsupported=include+lib  -DSIM_COMPILER="GCC Version:
 >      12.5.0" -DSIM_BUILD_TOOL=simh-makefile -I .  -D_GNU_SOURCE -DHAVE_PCRE_H
 >      -DHAVE_SEMAPHORE -DHAVE_SYS_IOCTL -DSIM_HAVE_DLOPEN=so -DHAVE_EDITLINE
 >      -DHAVE_UTIME -DHAVE_LIBPNG -DHAVE_ZLIB -DHAVE_GLOB -DHAVE_SHM_OPEN
 >      ./VAX/vax_cpu.c ./VAX/vax_cpu1.c ./VAX/vax_fpa.c ./VAX/vax_io.c
 >      ./VAX/vax_cis.c ./VAX/vax_octa.c  ./VAX/vax_cmode.c./VAX/vax_mmu.c
 >      ./VAX/vax_stddev.c ./VAX/vax_sysdev.c ./VAX/vax_sys.c  ./VAX/vax_syscm.c
 >      ./VAX/vax_syslist.c ./VAX/vax_vc.c ./VAX/vax_lk.c ./VAX/vax_vs.c
 >      ./VAX/vax_2681.c ./PDP11/pdp11_rl.c ./PDP11/pdp11_rq.c
 >      ./PDP11/pdp11_ts.c ./PDP11/pdp11_dz.c ./PDP11/pdp11_lp.c
 >      ./PDP11/pdp11_tq.c ./PDP11/pdp11_xq.c ./PDP11/pdp11_vh.c
 >      ./PDP11/pdp11_cr.c ./PDP11/pdp11_td.c ./PDP11/pdp11_io_lib.c
 >      ./PDP11/pdp11_dup.c ./scp.c ./sim_console.c ./sim_fio.c ./sim_timer.c
 >      ./sim_sock.c ./sim_tmxr.c ./sim_ether.c ./sim_tape.c ./sim_disk.c
 >      ./sim_serial.c ./sim_video.c ./sim_imd.c ./sim_card.c -DVM_VAX
 >      -DUSE_INT64 -DUSE_ADDR64 -DUSE_SIM_VIDEO -I ./VAX -I ./PDP11
 >      -DHAVE_PCAP_NETWORK -I/usr/include/pcap/ -DBPF_CONST_STRING
 >      -DUSE_NETWORK -DHAVE_VDE_NETWORK -DHAVE_TAP_NETWORK -DHAVE_BSDTUNTAP
 >      -Islirp -Islirp_glue -Islirp_glue/qemu -DHAVE_SLIRP_NETWORK
 >      -DUSE_SIMH_SLIRP_DEBUG slirp/*.c slirp_glue/*.c -DHAVE_LIBSDL
 >      -DUSE_SIM_VIDEO `sdl2-config --cflags` `sdl2-config --libs`
 >      -DUSE_READER_THREAD -DSIM_ASYNCH_IO -o BIN/vax  -Wl,-zrelro
 >      -L/usr/pkg/lib -Wl,-R/usr/pkg/lib -L/usr/X11R7/lib -Wl,-R/usr/X11R7/lib
 >      -L/usr/lib -Wl,-R/usr/lib -lm -lrt -lpthread -lpcre -L/usr/pkg/lib/
 >      -ledit -ltermcap -lpng16 -lz -lpcap -lvdeplug -Wl,-R,/usr/pkg/lib/
 >      -L/usr/pkg/lib/
 > 
 > (You can ignore references to VDE or vdeplug; this refers to wip/vde2)

 Compile command completely coincides except for VDE arguments.

 > Aside: the config line "load -r ka655x.bin" should not be needed, since
 > the same file is built-in. Simh will say "%SIM-INFO: Loading boot code
 > from internal ka655x.bin"

 I tried both internal and external ka655x.bin, but result does
 not changed.

 > It may be that adding -Wstrict-overflow=5 shows some useful diagnostic.

 Ah, yes, disabling -fno-strict-overflow and adding -Wstrict-overflow=5
 result in a lot of compiler warnings...

 > If this does not show any missing options, I have no objection if you
 > commit the changes you propose.

 As I couldn't reproduce the problem with public build of 2026Q3 for
 netbsd-11, I hesitate to commit my suggested changes...

 I will change this PR to analyzed until when anyone who can reproduce
 my problem.

 > -Olaf.

 Thanks,
 rin

>Unformatted:

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