Re: [Xen-devel] [PATCH for-4.7 1/5] build: make HOSTCC conditional on the value of clang

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Sun, Apr 17, 2016 at 02:03:28PM -0600, Jan Beulich wrote:
> >>> Roger Pau Monne <roger.pau@xxxxxxxxxx> 04/15/16 8:27 PM >>>
> >Previously HOSTCC was always hardcoded to gcc
> 
> So what is the goal here? Be able to build on a gcc-free system? Or else, how
> does it matter what compiler build elements get built with?

Exactly. Newish FreeBSD versions (>=10 IIRC) only have clang in the base 
system.
 
> >--- a/Config.mk
> >+++ b/Config.mk
> >@@ -36,7 +36,6 @@ CONFIG_$(XEN_OS) := y
>  >SHELL     ?= /bin/sh
>  >
>  ># Tools to run on system hosting the build
> >-HOSTCC      = gcc
>  >HOSTCFLAGS  = -Wall -Werror -Wstrict-prototypes -O2 -fomit-frame-pointer
>  >HOSTCFLAGS += -fno-strict-aliasing
>  >
> >@@ -50,8 +49,10 @@ DESTDIR     ?= /
>  >clang ?= n
>  >ifeq ($(clang),n)
>  >gcc := y
> >+HOSTCC = gcc
>  >else
>  >gcc := n
> >+HOSTCC = clang
>  >endif
>  
>  In particular I wonder what this means for cross builds, where someone may
> have installed e.g. only a cross variant of clang.

Right, I think this should be ?= instead of =, so if a user has HOSTCC set 
in the build environment the build system doesn't overwrite it.
 
> That said, I'm not really opposed to the change (as it seems to be at least an
> incremental improvement), I only wonder whether some more thought (and
> change) is needed here.

IMHO, I think using ?= should at least be more correct, or if anyone has a 
better suggestion I'm happy to implement it.

Roger.

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