It doesn’t hit on the breakpoints for some reason.  I’m most likely doing something wrong.

GNU gdb 4.17
Copyright 1998 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain conditions.
Type “show copying” to see the conditions.
There is absolutely no warranty for GDB. Type “show warranty” for details.
This GDB was configured as “–host=i486-pc-netbsd –target=i386-linux-gnuaout”…
Setting up the environment for debugging gdb.
Breakpoint 1 at 0x94a4: file panic.c, line 18.
Breakpoint 2 at 0x667b: file init/main.c, line 110.
tcp_open ! localhost:1234
0xfff0 in sys_unlink () at memory.c:430
430 }
(top-gdb)c
Continuing.

Program received signal SIGINT, Interrupt.
panic (s=0x1dd6c “”) at panic.c:23
23 for(;;);
(top-gdb)bt
#0 panic (s=0x1dd6c “”) at panic.c:23
#1 0xd9b3 in mount_root () at memory.c:430
#2 0x12f39 in sys_setup (BIOS=0x1ab38) at hd.c:157
#3 0x7477 in system_call () at sched.c:412
#4 0x1000000 in ?? ()
(top-gdb)

But after a LOT of struggling it certainly looks about right.

I then went ahead and built GDB 8.0.1, and it’s incredibly slow, and I guess not too compatible with Qemu 0.9 (I had issues with newer builds though) but it does break.

(top-gdb)target remote localhost:1234
Remote debugging using localhost:1234
0x0000fff0 in sys_unlink () at memory.c:83
83 }
(top-gdb)i b
Num Type Disp Enb Address What
1 breakpoint keep y 0x000094a4 in panic at panic.c:18
2 breakpoint keep y 0x000094a4 in panic at panic.c:18
silent
return
(top-gdb)c
Continuing.

Breakpoint 1, panic (s=0xd8cf <sys_mount+227>) at panic.c:18
18 printk(“Kernel panic: %s\n\r”,s);
Reply contains invalid hex digit 79
(top-gdb)i s
Reply contains invalid hex digit 79
(top-gdb)bt
#0 0x0000d9b3 in mount_root () at memory.c:83
#1 0x0001ab60 in hd_info ()
#2 0x00000000 in ?? ()
(top-gdb)i r
eax 0x0 0
ecx 0x51 81
edx 0x1fb4c 129868
ebx 0x0 0
esp 0xffff94 0xffff94
ebp 0xffffa8 0xffffa8
esi 0x1ab60 109408
edi 0x0 0
eip 0xd9b3 0xd9b3 <mount_root+139>
eflags 0x246 [ PF ZF IF ]
cs 0x8 8
ss 0x10 16
ds 0x10 16
es 0x10 16
fs 0x17 23
gs 0x17 23
(top-gdb)

And while it more or less runs there is some issues using the GDB stub from Qemu 0.9.0, although I had a world of pain with newer versions.  And I’ve never done the kernel debug thing before so this is all new to me.

And I guess it goes as no surprise that with GDB 8, they have a.out Linux tagged as obsolete and to be removed.  I guess I need to try a GDB that was current to Qemu 0.90 so it may not have so many packet overruns and unexpected results…