Re: [Xen-devel] Implementaiton of cc-option in Config.mk

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Thu, Mar 15, 2018 at 02:45:15AM -0600, Jan Beulich wrote:
> >>> On 14.03.18 at 18:11, <wei.liu2@xxxxxxxxxx> wrote:
> > The implementation of cc-option (grepping the option being tested in
> > output) in Config.mk now makes it not possible to detect if -Og is
> > supported because "-Og" doesn't appear in the output if it is not
> > supported. I suspect there will be other options that cc-option can't work
> > with.
> > 
> > It is implemented like that because we try to detect -Wno-* option. But
> > why is that important? Can't we just ignore -Wno-* if they aren't
> > supported?
> 
> Well, the explanation for its behavior is given in the comment
> next to its definition:

Yeah, I know that. I'm just not sure why nonexistent -Wno-* should be
rejected. If there is no corresponding -W* option in the first place,
-Wno-* shouldn't cause any difference in the end result.

> 
> # This is complicated by the fact that unrecognised -Wno-* options:
> #   (a) are ignored unless the compilation emits a warning; and
> #   (b) even then produce a warning rather than an error
> 
> > Does anyone has an idea how to make cc-option work for -Og
> > (and other options)?
> 
> How about simply extending it to also use the "test failed"
> alternative if the compilation produced an error status (which
> is currently ignored by way of the use of a pipeline)? Untested:
> 
> cc-option = $(shell if test -z "`echo 'void*p=1;' | \
>               { $(1) $(2) -S -o /dev/null -x c - 2>&1 || echo $(2); } | grep 
> -- $(2) -`"; \
>               then echo "$(2)"; else echo "$(3)"; fi ;)
> 

Yeah, let me try this.

Wei.

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