Improve gdbstub docs to point out sw breakpoints are hard to insert in early kernel code before maps and relocation are done.
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## Goal
When remote debugging a qemu VM with -enable-kvm running the Linux Kernel v 6.14.1, I realized that software breakpoints fail to be inserted.
## Technical details
While I am aware that GDB with qemu-kvm support has not been prioritized(as mentioned in this issue: https://gitlab.com/qemu-project/qemu/-/work_items/2991) I would like to work on this issue, improving the state of breakpoint support for qemu-kvm.
I have already spent some time debugging the issue of not being able to insert software breakpoints, and there seems to be an error thrown by `memory_region_access_valid`, as the memory region is set to `io_mem_unassigned`. Was wondering where to go from here and also in general for pointers in improving this issue
## Additional Information
In case this is a bug on my end, here's my configuration and steps to reproduce:
Host:
Ubuntu LTS(Kernel v6.17.12) running on distrobox
qemu-systemx86_64 v11.0.50 (although this happens in my Fedora host running qemu-system-x86_64 version 10.1.3 as well)
Guest:
Linux Kernel version 6.14.1.
Command Used:
```bash
qemu-system-x86_64 -kernel /path/to/kernel-build/arch/x86/boot/bzImage \
-enable-kvm \
-cpu host \
-nographic \
-m 256M \
-no-reboot \
-append "console=ttyS0 loglevel=7 nokaslr" \
```
Step-1: Run the command and connect via GDB client on port 1234
Step-2: Break at 'start_kernel' and continue.
Result: GDB reports the error: 'Cannot insert breakpoint 1, Cannot access address at.."
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issue