[SeaBIOS] POST Memory Manager emulation in SeaBIOS

Kevin O'Connor kevin at koconnor.net
Tue Oct 11 02:01:45 CEST 2011

On Mon, Oct 10, 2011 at 03:32:06PM +0700, Darmawan Salihun wrote:
> Hi guys,
> I'm currently debugging a generic PCI Option ROM
> (seen as legacy ROM since there is no PnP header).
> This is the setup:
> a. The Option ROM "merged" to coreboot binary as CBFS component
> (./cbfstool  <option-rom-path> genroms/option-rom.rom raw)
> b. SeaBIOS would recognize the Option ROM and execute it. The execution
> seems to take place after most PnP option ROM.
> c. Coreboot+Seabios is running inside qemu.
> d. The entire process (qemu with coreboot as "BIOS") is debugged remotely
> using IDA Pro. The connection is through GDB remote debugging "plugin"
> in IDA Pro.
> Therefore, from Qemu persepective, its being debugged remotely by GDB.
> Now, my question:
> In this particular option ROM, a call to POST Memory Manager (PMM) is made
> to allocate 64KB of memory. What "reaction" SeaBIOS would carry-out to
> such request?

Calls to PMM start at romlayout.S:entry_pmm which will transition the
cpu to 32bit mode and call pmm.c:handle_pmm().  An allocation call
should reserve the memory and return a pointer to it.

PMM debug info is on by default, so you should see SeaBIOS write debug
info to the serial port.

> I've trying to debug this call but nothing seems to happen as I see it
> from inside IDA Pro.
> Any clues? or where should I peek in the source code?

I suggest getting serial debugging working, and post the full log.


> TIA,
> Darmawan

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