Cannot debug init using "qemu -s -S" if init is compiled dynamically or if kvm is enabled

Host environment

• QEMU flavor: qemu-system-x86_64
• Operating system: Debian sid (as of 2022-10-22)
• OS/kernel version: Linux 6.0.0-1-amd64
• Architecture: x86_64
• QEMU version: QEMU emulator version 7.1.0 (Debian 1:7.1+dfsg-2+b1)
• QEMU command line: qemu-system-x86_64 -daemonize -m 300M -s -S -kernel /vmlinuz -initrd /initrd.img -snapshot -append "root=/dev/sda init=/root/a.out" -drive file=/dev/sda,format=raw

Emulated/Virtualized environment

• Operating system: Debian sid (as of 2022-10-22)
• OS/kernel version: Linux 6.0.0-1-amd64
• Architecture: x86_64

Description of problem

I'm trying to connect from host to init process running in guest. I'm using this guide: https://qemu-project.gitlab.io/qemu/system/gdb.html . Everything works well, but there is two problems:

1. Debugging stops to work if I add "-enable-kvm"
2. Debugging stops to work if I remove "-static" when compiling init

Steps to reproduce

I have absolutely fresh Debian sid system (as of 2022-10-22). I create the following file on it:

#include <stdio.h>

int
main ()
{
  printf ("a\n");
  printf ("b\n");
  for (;;);
}

Then I compile it so: gcc -static -g a.c. Result is saved as /root/a.out. Then I run sync; echo 3 > /proc/sys/vm/drop_caches; sync to make sure this /root/a.out actually got to disk.

Then I start the host system inside of qemu using well-known -snapshot /dev/sda trick. Exact command is here:

qemu-system-x86_64 -daemonize -m 300M -s -S -kernel /vmlinuz -initrd /initrd.img -snapshot -append "root=/dev/sda init=/root/a.out" -drive file=/dev/sda,format=raw

(As you guessed, my disk has no partitions, it directly stores ext4 filesystem.)

Then I type on host gdb ./a.out. And then inside of gdb I type target remote localhost:1234, then br 7 (line 7 is printf ("b\n"), then c. Then guest OS boots and reaches init (i. e. /root/a.out). And then gdb actually pauses on line 7. I. e. everything works!

But if I add -enable-kvm to qemu command line OR remove -static from gcc command line, then breakpoint doesn't work, i. e. gdb doesn't pause on breakpoint, the execution continues and the execution fails to infinite loop.