Re: pkg/60875 (open-simh: miscompiled by GCC on NetBSD/amd64)

[Rhialto <rhialto%falu.nl@localhost>]

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 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)

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"

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

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

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