Re: [PATCH trace-cmd 3/3] Revert "trace-cmd: Use conditional assignmentof CC and AR"

[Darren Hart]

On 03/09/2011 06:27 PM, David Sharp wrote:
> On Wed, Mar 9, 2011 at 5:58 PM, Darren Hart<dvhart@xxxxxxxxxxxxxxx>  wrote:
> > On 03/09/2011 05:36 PM, Steven Rostedt wrote:
> > > On Wed, 2011-03-09 at 17:27 -0800, Darren Hart wrote:
> > > > On 03/09/2011 03:58 PM, David Sharp wrote:
> > > > > This reverts commit 6c696cec3f264a9399241b6e648f58bc97117d49.
> > > > >
> > > > > Make has default values CC and AR of 'cc' and 'ar' respectively. This
> > > > > means
> > > > > that "CC ?= anything" will never have effect, because CC is always
> > > > > already set.
> > > > > Because of this, 6c696cec makes setting CROSS_COMPILE from the command
> > > > > line or
> > > > > environment useless.
> > > >
> > > > The problem with this approach is it prevents the user from setting CC
> > > > explicitly with the environment which is a very common way of using a
> > > > specific version of gcc (for example). It also places restrictions on
> > > > the filename of the compiler (it must end in gcc - so gcc-4.5.1 cannot
> > > > work), this isn't acceptable.
> > > >
> > > > You could use CC=your-cross-compiler, and if that doesn't work for you,
> > > > you could prepare a patch that conditionally sets CC only if
> > > > CROSS_COMPILE is set, but please do not simply revert this patch which
> > > > solved a real problem with the Makefile.
> > >
> > > Hmm, but the thing is, the change did not work,
> >
> > It did work for me as I was setting CC= on the command line.
> >
> > unless your environment
> > > for some reason does not supply a 'cc'. Or that 'cc' defaulted to the
> > > compiler that you wanted, where 'gcc' would not.
> > >
> > > Thus, would you be fine with something like:
> > >
> > >         BUILD_CC ?=     $(CROSS_COMPILE)gcc
> > >         CC       =      $(BUILD_CC)
> >
> > This would also work, but what is wrong with:
> >
> > dvhart@doubt:templates$ cat Makefile
> > ifdef CROSS_COMPILE
> > CC = $(CROSS_COMPILE)gcc
> > AR = $(CROSS_COMPILE)ar
> > endif
> >
> > all:
> >         echo "CC: $(CC)"
> >
> > dvhart@doubt:templates$ make -s
> > CC: cc
> >
> > dvhart@doubt:templates$ CC=gcc-4.5.1 make -s
> > CC: gcc-4.5.1
> >
> > dvhart@doubt:templates$ CROSS_COMPILE=my-cross- make -s
> > CC: my-cross-gcc
> >
> >
> > Seems to meet everyone's needs without changing any tools/scripts/etc that
> > have used trace-cmd before or after the CC ?= wreckage.
>
> It's a little odd that the default CC is "cc" unless you supply
> CROSS_COMPILE, then it's "gcc". I'd probably be okay with this, but I
> would think it's weird.
>
> I don't know the answers, but if we take the kernel Makefile as a
> template, then setting CC doesn't work.

The kernel is a bit special I believe as it is pretty tied to gcc. Is 
trace-cmd tied to gcc to such a degree that we want to make it difficult 
for people to try different compilers?

--
Darren
Intel Open Source Technology Center
Yocto Project - Linux Kernel
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