debugging with gdb and qemu

[az20110303]

I launched qemu virtual machine with this options

qemu-system-x86_64 -s -S

I did not set any data images because i just want to try gdb. I am going to spet some instructions through BIOS startup code.

So i connected to virtual machine with gdb

(gdb) target remote localhost:1234
Remote debugging using localhost:1234
0x0000fff0 in ?? ()

Now that what i do

(gdb) x/i $pc
=> 0xfff0: add %al,(%eax)
(gdb) display/i $pc
1: x/i $pc
=> 0xfff0: add %al,(%eax)
(gdb) si
0x0000e05b in ?? ()
1: x/i $pc
=> 0xe05b: add %al,(%eax)
(gdb) si
0x0000c81e in ?? ()
1: x/i $pc
=> 0xc81e: add %al,(%eax)
(gdb) si
0x0000c821 in ?? ()
1: x/i $pc
=> 0xc821: add %al,(%eax)
(gdb) si
0x0000c827 in ?? ()
1: x/i $pc
=> 0xc827: add %al,(%eax)
(gdb)

As you see for some reason all instructions in memory are displayed as

add %al,(%eax)

This is equivalent as if the whole memory contained zeroes. But it doesn't! You see ho $pc changes? it does not increment 2 bytes all the time.
What the promblem with gdb agai???

[Lakshmipathi]

I don't know about how to debug using qemu. But you want to debug kernel source code -then using User mode linux is an easy/better approach.