Re: [Xen-devel] [PATCH v4] tools: detect appropriate debug optimization level

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Wed, Mar 14, 2018 at 02:16:31PM +0000, Wei Liu wrote:
> On Mon, Mar 12, 2018 at 11:06:51PM -0500, Doug Goldstein wrote:
> > When building debug use -Og as the optimization level if its available,
> > otherwise retain the use of -O0. -Og has been added by GCC to enable all
> > optimizations that to not affect debugging while retaining full
> > debugability.
> > 
> > Signed-off-by: Doug Goldstein <cardoe@xxxxxxxxxx>
> > ---
> >  tools/Rules.mk | 9 +++++++--
> >  1 file changed, 7 insertions(+), 2 deletions(-)
> > 
> > diff --git a/tools/Rules.mk b/tools/Rules.mk
> > index 296b722372..3848bcf1f7 100644
> > --- a/tools/Rules.mk
> > +++ b/tools/Rules.mk
> > @@ -164,8 +164,13 @@ LDLIBS_libxenvchan = $(SHDEPS_libxenvchan) 
> > $(XEN_LIBVCHAN)/libxenvchan$(libexten
> >  SHLIB_libxenvchan  = $(SHDEPS_libxenvchan) -Wl,-rpath-link=$(XEN_LIBVCHAN)
> >  
> >  ifeq ($(debug),y)
> > -# Disable optimizations
> > -CFLAGS += -O0 -fno-omit-frame-pointer
> > +CFLAGS += -fno-omit-frame-pointer
> > +# Use optimizations compatible with debugging otherwise disable 
> > optimizations
> > +ifneq ($(call cc-option,$(CC),-Og,n),n)
> > +CFLAGS += -Og
> > +else
> > +CFLAGS += -O0
> > +endif
> 
> Sadly the way cc-option is written made the support check always
> return true. cc-option would grep for -Og in the (error) to tell if
> it is supported or not, but the error message for -Og doesn't contain
> "-Og". It is like 
> 
>   cc1: error: argument to '-O' should be a non-negative integer
> 
> We need to think of another way to test it, or we just have to live with
> V1.

Wait, but even v1 is bogus because cc-option-add uses cc-option.

I'm afraid we will need to figure out a new way to detect if the option
is supported.

Wei.

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