So I’m trying to force a break in a program to look at the call stack.  Normally pretty easy stuff as far as adding breakpoints or the random i=j/0 type thing to force a div0 exception etc.

But I’ve been going crazy with this fun error:

gdb: unknown target exception 0x4000001f at 0x453b1c

And I should have checked my path earlier, as even though I’m using the 32bit version of GCC, the TDM-GCC project bundles their 32bit GDB as gdb32.exe .  Ouch.  The other hint of course was in the banner:

GNU gdb (GDB) 7.9.1
Copyright (C) 2015 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type “show copying”
and “show warranty” for details.
This GDB was configured as “x86_64-w64-mingw32”.

Yeah, further oops, in actually paying attention to how it executes:

(gdb) r
Starting program: C:\temp\dynamips\dynamips.exe -P 1700 -s 0:0:gen_eth:”\Device\NPF_{2F7A0E3F-0908-4489-8117-475A6AD299A6}” C1700-Y-.BIN -j
[New Thread 2696.0x22b0]
warning: `C:\WINDOWS\SYSTEM32\ntdll.dll’: Shared library architecture i386:x86-64 is not compatible with target architecture i386.
warning: `C:\WINDOWS\system32\wow64.dll’: Shared library architecture i386:x86-64 is not compatible with target architecture i386.
warning: `C:\WINDOWS\system32\wow64win.dll’: Shared library architecture i386:x86-64 is not compatible with target architecture i386.
warning: Could not load shared library symbols for WOW64_IMAGE_SECTION.
Do you need “set solib-search-path” or “set sysroot”?
warning: Could not load shared library symbols for WOW64_IMAGE_SECTION.
Do you need “set solib-search-path” or “set sysroot”?
warning: Could not load shared library symbols for NOT_AN_IMAGE.
Do you need “set solib-search-path” or “set sysroot”?
warning: Could not load shared library symbols for NOT_AN_IMAGE.
Do you need “set solib-search-path” or “set sysroot”?
warning: `C:\WINDOWS\system32\wow64cpu.dll’: Shared library architecture i386:x86-64 is not compatible with target architecture i386.
[New Thread 2696.0xabc]

Great.

So it’s not some exciting bug, but rather the 64bit version of gdb can kick off a 32bit exe, but it’ll get lost inside.  The proper 32bit GDB looks like this:

C:\temp\dynamips>gdb32.exe dynamips.exe
GNU gdb (GDB) 7.9.1
Copyright (C) 2015 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type “show copying”
and “show warranty” for details.
This GDB was configured as “mingw32”.

And sure enough the call stack works fine.

Breakpoint 1, 0x00453b1c in mpc860_fec_set_nio ()
(gdb) bt
#0 0x00453b1c in mpc860_fec_set_nio ()
#1 0x004827e2 in dev_c1700_mb_eth_set_nio ()
#2 0x0044abdf in cisco_card_enable_all_nio ()
#3 0x0044b9df in vm_slot_enable_all_nio ()
#4 0x0044bb0e in vm_slot_init ()
#5 0x0044bb36 in vm_slot_init_all ()
#6 0x00481b5d in c1700_init_platform ()
#7 0x00481dc3 in c1700_init_instance ()
#8 0x004155b3 in vm_init_instance ()
#9 0x004125dc in main ()
(gdb)

Wasn’t that fun?!