Re: [Xen-devel] [Qemu-devel] Question to prefered

[Sander Eikelenboom <linux@xxxxxxxxxxxxxx>]

Thursday, April 11, 2013, 9:50:09 PM, you wrote:

> On 11 April 2013 20:32, Sander Eikelenboom <linux@xxxxxxxxxxxxxx> wrote:
>> Hi Paolo / Anthony,
>> 2) Qemu seems to have the possibility to make a debug enabled build by 
>> specifing --enable-debug option to ./configure,
>>    that sets CONFIG_DEBUG_EXEC=y, but a grep on CONFIG_DEBUG_EXEC seems to 
>> indicate it's not in widespread use ..

> --enable-debug does several things:
>  * turns on --enable-debug-tcg
>  * does not compile with optimization
>  * does not strip the binaries
>  * turns on the CONFIG_DEBUG_EXEC flag to enable '-d exec'

>>    - Why is it not named CONFIG_DEBUG ?

> Because CONFIG_DEBUG_EXEC is not a general purpose 'turn on debug logs'
> switch. It has a specific meaning: "make the '-d exec' debug log command
> line option work". Note that it does not cause QEMU to emit any
> extra logging unless requested at runtime.

> In fact, since the only overhead of CONFIG_DEBUG_EXEC is a single
> qemu_log_mask() call I think I might submit a patch to drop it
> entirely and just always have -d exec work...

>>    - Is it the right config to use to swith on verbose debugging
>> in the xen files.

> No. It depends a bit what you mean by "verbose debugging",
> incidentally. QEMU has several commonly used logging options:

Well since Xen has the option to be build with "make debug=y" which also 
disables optimizations, enables extra asserts and makes it more verbose.
It could be handy to propagate that to the qemu-binary that is built in the 
xen-tree to also be more verbose if it's built as part of a debug build.

That way you can ask a user to build a debug build, and not have a user edit to 
much source to enable all the defines.

Apart from that the current xen-files in upstream qemu are much less verbose 
than the old forked in tree qemu-traditional was, so that will also require 
some adjustment.

Would a "--enable-debug-xen" config option be acceptable ?

> (1) per-source file #defines which you can turn on as a developer
> to get a lot of debug printf output
> (2) the -d command line option, which lets the user enable
> certain classes of logging by category (for example, this is
> the best way to log "the guest did something weird which is
> probably a guest bug" or "the guest tried to access something
> we don't implement")
> (3) tracepoints (see docs/tracing.txt)

> -- PMM



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