Re: [Qemu-devel] Qemu as Instruction Set Simulator without any OS

[Robin Randhawa <robin.randhawa@gmail.com>]

Hi again.

On Wed, Sep 01, 2010 at 06:24:41pm +0530, Anitha Boyapati wrote:
> Hello Robin,
[...]
> 
> >> 2. Can QEMU be used as a simple instruction set simulator with
> >> probably gdb support for remote debugging? My guess is this would
> >> require a bootloader to load the application to run the application
> >> program (full system emulation mode or just machine emulation if
> >> there is something like that). If yes, what else can be the blocker
> >> to have gdb support?
> >
> > IMHO, gdb support if available, is available irrespective of the
> > type and nature of the software being run on qemu. For example, you
> > can create a bare-metal application that executes from the reset
> > vector for say, the ARM or the MIPS models and have gdb support
> > right from the outset. There is no explicit need for running boot
> > firmware and/or a loader to load an application program. Not sure if
> > that's what you were after.
> 
> My exact requirement is to test a gcc cross-compiler using DejaGnu for
> a given target (AVR32). While the cross-compiler is ready, there is no
> simulator. Since there is not much of OS support, I am trying to
> evaluate if Qemu can still be considered for this purpose.

I see. That makes sense. I thought that AVR32 support never made it to
the mainline. Has that changed ?
 
> The usage scenario probably goes like this:
> 
> 1. Qemu-target should be invoked with the application (yes,
> bare-metal) waiting for some gdb connection.  2. target-gdb is invoked
> with the same application
> 
> I am referring to the example given in
> http://wiki.qemu.org/download/qemu-doc.html#gdb_005fusage :
> 
> > qemu -s -kernel arch/i386/boot/bzImage -hda root-2.4.20.img -append
> > "root=/dev/hda"
> 
> However, in my case kernel image doesn't exist. 

Got that. Note that your system mode emulation would have to cater for
loading the bare-metal image (qemu has well defined APIs for this). Some
emulations add some intelligence over and above the bare-metal image
loading, such as the ARM Realview emulation which checks to see if the
image passed to the "-kernel" argument is a Linux image in which case
some special case initialisation is done (instead of a 'raw' load).

> As to the requirement
> of bootloader, I need to investigate further as various types of
> memories (FLASH & SRAM for program and data sections) exist.

Most of that can be easily faked as simple RAM at the appropriate
offsets in your platform description to start off with.
 
> > This does require system-mode emulation support as opposed to
> > user-mode emulation for your microcontroller to be implemented.
> 
> Agreed. System-mode emulation is what is required.

Cheers,
Robin