Re: [Xen-devel] [PATCH] libxl/Makefile: Don't optimize debug builds; add macro debugging information

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2014-12-01 at 11:55 +0000, Euan Harris wrote:
> On Mon, Dec 01, 2014 at 11:43:13AM +0000, Ian Campbell wrote:
> > On Mon, 2014-12-01 at 10:39 +0000, Euan Harris wrote:
> > > libxl debug builds are built with optimization level -O1, inherited from
> > > the CFLAGS definition in StdGNU.mk.   Optimizations confuse the debugger,
> > > and the comment justifying -O1 in StdGNU.mk should not apply for a
> > > userspace library.   Disable optimization by appending -O0 to CFLAGS,
> > > which overrides the -O1 flag specified earlier.
> > 
> > I think if this argument applies (I see no reason to disagree) then it
> > should apply to the whole of tools/* or at least to tools/lib* and not
> > just to libxl. IOW this probably belongs at a higher level somewhere.
> 
> Ok, I'll submit a new patch putting it in tools/Rules.mk

Thanks.

> > > Also specify -g3, to add macro debugging information which allows
> > > gdb to expand macro invocations.   This is useful as libxl uses many
> > > non-trivial macros.
> > 
> > Useful, I'd never heard of this. Do you know which version of gcc
> > introduced it? (AKA do we need to make it part of configure.ac to check
> > availability or not).
> 
> It's documented in GCC 2.95.3 [1], which is as far back as the online
> manuals go.
> 
> [1] https://gcc.gnu.org/onlinedocs/gcc-2.95.3/gcc_2.html#SEC9

OK, I'm pretty sure that's (way....) before our cut-off. Thanks.

> > Not sure if you were proposing this change for 4.5 or not.
> 
> It would be nice to have, but I was assuming that 4.5 was more or less
> closed by now.

Exceptions can be asked/argued for. I'd be a bit wary of something like
this since the knock-on effects might be a bit subtle. Completely fine
during a dev window though.

Ian.


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