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Re: [Qemu-devel] Question to prefered

From: Peter Maydell
Subject: Re: [Qemu-devel] Question to prefered
Date: Thu, 11 Apr 2013 20:50:09 +0100

On 11 April 2013 20:32, Sander Eikelenboom <address@hidden> 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:

(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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