[coreboot] Help debugging qemu + coreboot using GDB

[Ni, Ray]

Hi experts,
I built a coreboot image with following steps for tracing coreboot ramstage flow:

1.  make menuconfig
---
CONFIG_BOARD_EMULATION_QEMU_X86_Q35=y
CONFIG_GDB_STUB=y
CONFIG_GDB_WAIT=y
---

1.  make crossgcc-i386
  2.  make

Then I start gdb:

1.  gdb
  2.  (gdb) file /mnt/e/work/coreboot/build/cbfs/fallback/ramstage.debug

Reading symbols from /mnt/e/work/coreboot/build/cbfs/fallback/ramstage.debug...

1.  (gdb) target remote:1234

Then I start QEMU:

1.  qemu-system-i386  --bios build/coreboot.rom -nographic -M q35 -s
--- tty out put as below ---
...
Timestamp - finished loading ramstage: 627985288
BS: postcar times (exec / console): total (unknown) / 80 ms
$S02#b5$S02#b5$S02#b5$S02#b5$S02#b5$S02#b5$S02#b5$S02#b5$S02#b5$S02#
------------
(The "$S02#B5" repeats infinitely. I guess it's to report a stop event to GDB.)

The GDB successfully connects to coreboot.
"disassemble $eip, +20" works fine.
"n" command doesn't work.
(gdb) n
Cannot find bounds of current function

What mistake I might make?

Thanks,
Ray