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Re: [Qemu-devel] Support for using TCG frontend as a library


From: Liviu Ionescu
Subject: Re: [Qemu-devel] Support for using TCG frontend as a library
Date: Fri, 2 Dec 2016 12:12:45 +0200

> On 2 Dec 2016, at 11:40, Peter Maydell <address@hidden> wrote:
> 
>> ... integrate this feature in the usual debugging workflow.
> 
> The most useful approach is that you can set up a complicated
> situation (eg "boot my embedded RTOS, start application"),
> snapshot at that point, and then you can repeatedly restart
> debugging from the snapshot without having to take ages going
> through the bootup process each time. (Particularly useful if
> you turn on heavyweight tracing which can turn bootup from
> "fairly fast" to "incredibly slow".)

I see your point, and I'm convinced that for your use cases booting linux and 
starting applications is a big deal of effort.

for the bare metal use cases, "going through the bootup process" is quite 
lightwheight, setting a few registers and the application starts.

as for integration with the current workflow, it might be done, but it requires 
quite a lot of efforts, and the results are only for a very limited audience, 
if any.

on the other side, what would be really useful for Cortex-M, are the 
instruction and data tracing features available for some devices, usually 
available only with very expensive multi-pin JTAG probes on physical devices; 
were these ARM features considered?

---

to summarise, the requirements for emulating Cortex-M devices are much, much 
lower than for your current large targets using OSes.

as a result, I'm seriously considering simplifying the GNU ARM Eclipse QEMU 
setup and tapping directly into the TCG, so packing it as a library will 
definitely be a useful feature.


regards,

Liviu




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