Bringing up graphical window with SDL crashes when interactive debugger happens

[NattyNarwhal]

I'm trying to use the debugger to poke ARC (#13), but enabling it (CMake debug build, CXXFLAGS="-DIDB") causes a segfault when the graphical window pops up.

[calvin@salient build]$ gdb --args ./axpbox run
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Reading symbols from ./axpbox...
(gdb) run
Starting program: /home/calvin/src/axpbox/build/axpbox run
Missing separate debuginfos, use: dnf debuginfo-install glibc-2.31-2.fc32.x86_64
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
%GUI-I-INS: Installing sdl module as the ES40 GUI
sys0(tsunami): $Id: System.cpp,v 1.79 2008/06/12 07:29:44 iamcamiel Exp $
%FLS-F-NOREST: Flash could not be restored from rom/flash.rom
sys0(tsunami): $Id: Flash.cpp,v 1.19 2008/03/24 22:11:50 iamcamiel Exp $
dma: $Id: DMA.cpp,v 1.9 2008/04/29 09:24:52 iamcamiel Exp $
pci0.19(ali_usb): $Id: AliM1543C_usb.cpp,v 1.6 2008/03/14 15:30:50 iamcamiel Exp $
%DPR-F-NOREST: DPR could not be restored from rom/dpr.rom
sys0(tsunami): $Id: DPR.cpp,v 1.23 2008/06/12 07:29:44 iamcamiel Exp $
cpu0(ev68cb)(0): $Id: AlphaCPU.cpp,v 1.82 2009/03/16 01:33:27 iamcamiel Exp $
serial0(serial): Waiting for connection on port 21264.
[Detaching after fork from child process 70146]
serial0(serial): $Id: Serial.cpp,v 1.51 2008/06/03 09:07:56 iamcamiel Exp $
serial1(serial): Waiting for connection on port 21265.
[Detaching after fork from child process 70152]
serial1(serial): $Id: Serial.cpp,v 1.51 2008/06/03 09:07:56 iamcamiel Exp $
%IDE-I-INIT: New IDE emulator initialized.
pci0.1(cirrus): $Id: Cirrus.cpp,v 1.23 2008/05/31 15:47:09 iamcamiel Exp $
pci0.7(ali): $Id: AliM1543C.cpp,v 1.66 2008/05/31 15:47:07 iamcamiel Exp $
kbc: $Id: Keyboard.cpp,v 1.10 2008/05/31 15:47:09 iamcamiel Exp $
%SYS-I-READROM: Reading decompressed ROM image from rom/decompressed.rom.
%SYM-I-PATCHROM: Patching ROM for speed.
%SYS-I-ROMLOADED: ROM Image loaded successfully!
%DPR-F-NOREST: DPR could not be restored from rom/dpr.rom
sys0(tsunami): $Id: DPR.cpp,v 1.23 2008/06/12 07:29:44 iamcamiel Exp $
This is the ES40 interactive debugger. To start non-interactively, run es40,
Or run this executable (es40_idb) with a last argument of @<script-file>
IDB 0000000000008000 P>run
%IDB-F-NOBRKP: No breakpoint set, press Ctrl-C to end run.
Arbitration 0000000000010000 from CPU 0 (@13e39)... won  0000000800010000
Arbitration clear from CPU 0 (@13f55).
Arbitration 0000000000010000 from CPU 0 (@13351)... won  0000000800010000
Arbitration clear from CPU 0 (@133b9).
Arbitration 0000000000010000 from CPU 0 (@13351)... won  0000000800010000
Arbitration clear from CPU 0 (@133b9).
Arbitration 0000000000010000 from CPU 0 (@13351)... won  0000000800010000
Arbitration clear from CPU 0 (@133b9).
cirrus: VGABios $Id: vgabios.c 226 2020-01-02 21:36:23Z vruppert $
cirrus: VBE Bios $Id: vbe.c 228 2020-01-02 23:09:02Z vruppert $
cirrus: vgabios call ah00 al03 bx95FA cx0000 dx03C5
cirrus: mode search 03 found line 03

Program received signal SIGSEGV, Segmentation fault.
0x00000000004e0f96 in bx_sdl_gui_c::palette_change (this=0x552a70, index=0, red=0, green=0, blue=0) at /home/calvin/src/axpbox/src/gui/sdl.cpp:1136
1136	  palette[index] = SDL_MapRGB(sdl_screen->format, palred, palgreen, palblue);
Missing separate debuginfos, use: dnf debuginfo-install SDL-1.2.15-43.fc32.x86_64 libX11-1.6.9-3.fc32.x86_64 libXau-1.0.9-3.fc32.x86_64 libgcc-10.1.1-1.fc32.x86_64 libpcap-1.9.1-3.fc32.x86_64 libstdc++-10.1.1-1.fc32.x86_64 libxcb-1.13.1-4.fc32.x86_64
(gdb) where
#0  0x00000000004e0f96 in bx_sdl_gui_c::palette_change (this=0x552a70, index=0, red=0, green=0, blue=0) at /home/calvin/src/axpbox/src/gui/sdl.cpp:1136
#1  0x000000000049c682 in CCirrus::write_b_3c9 (this=0x55a330, value=<optimized out>) at /home/calvin/src/axpbox/src/Cirrus.cpp:1564
#2  0x000000000049cc41 in CCirrus::io_write_b (this=<optimized out>, address=<optimized out>, data=<optimized out>) at /home/calvin/src/axpbox/src/Cirrus.cpp:896
#3  0x000000000049cd82 in CCirrus::io_write (this=0x55a330, address=969, dsize=<optimized out>, data=0) at /home/calvin/src/axpbox/src/Cirrus.cpp:849
#4  0x000000000049fb03 in CCirrus::WriteMem_Legacy (this=0x55a330, index=<optimized out>, address=<optimized out>, dsize=<optimized out>, data=<optimized out>) at /home/calvin/src/axpbox/src/Cirrus.cpp:509
#5  0x00000000004af22f in CPCIDevice::WriteMem (this=0x55a330, index=2, address=9, dsize=<optimized out>, data=0) at /home/calvin/src/axpbox/src/PCIDevice.cpp:397
#6  0x00000000004bd338 in CSystem::WriteMem (this=0x554c30, address=8804615848905, dsize=dsize@entry=8, data=0, source=source@entry=0x7ffff33d5010) at /home/calvin/src/axpbox/src/System.cpp:761
#7  0x00000000004157bc in CAlphaCPU::execute (this=0x7ffff33d5010) at /home/calvin/src/axpbox/src/AlphaCPU.cpp:842
#8  0x00000000004bc377 in CSystem::SingleStep (this=0x554c30) at /home/calvin/src/axpbox/src/System.cpp:575
#9  0x00000000004c0af3 in CTraceEngine::parse (this=this@entry=0x7ffff2d20010, command=command@entry=0x7fffffffaa30) at /home/calvin/src/axpbox/src/TraceEngine.cpp:989
#10 0x00000000004c21e1 in CTraceEngine::run_script (this=0x7ffff2d20010, filename=filename@entry=0x0) at /home/calvin/src/axpbox/src/TraceEngine.cpp:818
#11 0x000000000049b6e4 in main_sim (argc=argc@entry=1, argv=argv@entry=0x7fffffffd660) at /home/calvin/src/axpbox/src/AlphaSim.cpp:338
#12 0x00000000004ae098 in main (argc=2, argv=0x7fffffffd660) at /home/calvin/src/axpbox/src/Main.cpp:21

[lenticularis39]

It seems like the SDL screen isn't even created - at this point in the boot the SDL window should appear, but it does not. The debugger confirms that:

(gdb) p sdl_screen
$1 = (SDL_Surface *) 0x0

Thank you for reporting this, I'll have a look into it.

[lenticularis39]

So it's not only about the graphical window with SDL - the threads of all components are not started, because CSystem::start_threads() is not called when using IDB (usually it's called by CSystem::Run(), but here the trace engine takes control instead):

#if defined(IDB)
    if (argc > 1 && argc < 4 && argv[argc - 1][0] == '@')
      trc->run_script(argv[argc - 1] + 1);
    else
      trc->run_script(NULL);
#else
    theSystem->Run();
#endif

Adding a call to CSystem::start_threads() to the the RUN command of IDB helped with this, but the CPU seems not to execute any instructions - I'll try to fix it and commit the changes once it works.

Edit: Obviously CSystem::start_threads() also starts the CPU thread... that has to be resolved :D

[lenticularis39]

I'll push a fix for the problem that will close this issue - if you still have problems, feel free to reopen it.