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

From: Darren Hart
Date: Thu Mar 10 2011 - 01:43:37 EST


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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