Hi,
I'm using QEMU 0.8.2 to debug a new experimental OS (x86) I'm
currently writing for my university. So this is not based on Linux and
the "-kernel" option, instead I use a floppy image and load my kernel
using GRUB.
Now debugging was a breeze so far, but while implementing virtual
memory I'm hitting a huge problem. The kernel is loaded by GRUB at
physical address 0x100000 and, IIRC like Linux, I simply remap that to
be mirrored at 0xc0000000 using the page table. Afterwards I define my
kernel code and data segments to be based there as well, so that all
offsets in the code are still right. This works fine.
But after these initialisations I have problems with breakpoints:
(gdb) b timer_handler
Breakpoint 1 at 0x108294: file cpu_x86.c, line 29.
(gdb) c
now never returns, even though the code does run. If I do
(gdb) b *0xc0108294
Breakpoint 1 at 0xc0108294
(gdb) c
Continuing.
Program received signal SIGTRAP, Trace/breakpoint trap.
timer_handler at cpu_x86.c:71
I get the exception. Trying to continue with step or next results in a
complete GDB crash. It only works properly if I set both breakpoints:
(gdb) b timer_handler
Breakpoint 1 at 0x108294: file cpu_x86.c, line 29.
(gdb) b *0xc0108294
Breakpoint 2 at 0xc0108294
(gdb) c
Continuing.
Breakpoint 1, timer_handler at cpu_x86.c:71
Having to always set them both in the high and low area is a bit
cumbersome to say the least. Any suggestion on what I'm missing or can
do to get breakpoints working properly again?
Many thanks in advance, Marcel
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