Re: [Xen-devel] [PATCH] tools: build debug qemu-xen in debug tools builds

[Matthew Daley <mattjd@xxxxxxxxx>]

On Wed, Sep 4, 2013 at 3:32 AM, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:
> On Wed, 2013-09-04 at 01:12 +1200, Matthew Daley wrote:
>> When building tools in debug mode (debug=y), pass --enable-debug when
>> configuring qemu-xen to enable some debug support (namely, to prevent
>> symbols from being stripped).
>
> This is from the installed binaries I suppose?

Right, it stops the symbols from being stripped from the installed
binaries. The ones left in the build directory are not stripped
regardless.

> Is this the only affect or are there others?

The other changes I can see are to set
CONFIG_DEBUG_{TCG,MONITOR,EXEC}=y and, as Anthony said, to not add -O2
to CFLAGS (-g is added unconditionally).

AFAIK Xen doesn't use the subsystems where TCG/EXEC are mentioned, and
MONITOR just enables some extra error messages in the QEMU monitor
code anyway.

>
> I'd like some feedback from the qemu maintainers about whether this is
> an OK thing to do or not. Stefano/Anthony?
>
> Is it something we could consider doing unconditionally?

We could perhaps just configure with --disable-strip if we want to do
it unconditionally but still have optimization (for debug=n builds).
Debugging with -O2 isn't bad, but without symbols it's definitely more
annoying.

Looking at the current setup (without --enable-debug, FWIW) on my
machine, an unstripped binary is 18MB, while stripped is 4MB.

>
> Ian.
>
>>
>> Signed-off-by: Matthew Daley <mattjd@xxxxxxxxx>
>> ---
>>  tools/Makefile |    7 +++++++
>>  1 file changed, 7 insertions(+)
>>
>> diff --git a/tools/Makefile b/tools/Makefile
>> index 0531f48..066df66 100644
>> --- a/tools/Makefile
>> +++ b/tools/Makefile
>> @@ -173,6 +173,12 @@ qemu-xen-dir-force-update:
>>               $(GIT) reset --hard $(QEMU_UPSTREAM_REVISION); \
>>       fi
>>
>> +ifeq ($(debug),y)
>> +QEMU_XEN_ENABLE_DEBUG := --enable-debug
>> +else
>> +QEMU_XEN_ENABLE_DEBUG :=
>> +endif
>> +
>>  subdir-all-qemu-xen-dir: qemu-xen-dir-find
>>       if test -d $(QEMU_UPSTREAM_URL) ; then \
>>               source=$(QEMU_UPSTREAM_URL); \
>> @@ -181,6 +187,7 @@ subdir-all-qemu-xen-dir: qemu-xen-dir-find
>>       fi; \
>>       cd qemu-xen-dir; \
>>       $$source/configure --enable-xen --target-list=i386-softmmu \
>> +             $(QEMU_XEN_ENABLE_DEBUG) \
>>               --prefix=$(PREFIX) \
>>               --source-path=$$source \
>>               --extra-cflags="-I$(XEN_ROOT)/tools/include \
>
>

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