Re: [dpdk-dev] [EXT] Re: [PATCH v4 1/5] mk: introduce helper to check valid compiler argument

[Thomas Monjalon <thomas@monjalon.net>]

14/01/2019 12:56, Jerin Jacob Kollanukkaran:
> On Mon, 2019-01-14 at 12:35 +0100, Thomas Monjalon wrote:
> > -------------------------------------------------------------------
> > ---
> > 09/01/2019 11:39, Pavan Nikhilesh Bhagavatula:
> > > From: Jerin Jacob <jerinj@marvell.com>
> > > 
> > > Introduce rte_cc_has_argument() Makefile helper to
> > > check a given argument is support by the compiler.
> > > 
> > > Example Usage:
> > > 
> > > include $(RTE_SDK)/mk/rte.helper.mk
> > > MACHINE_CFLAGS += $(call rte_cc_has_argument, -mcpu=octeontx2)
> > > 
> > > This would allow adding -mcpu=octeontx2 in MACHINE_CFLAGS
> > > if it is only supported by the compiler. The use case for such
> > > scheme is to enable the mcpu optimization if the compiler
> > > supports else it needs to compile the source code without
> > > any errors.
> > > 
> > > This patch also moves inclusion of toolchain's rte.vars.mk
> > > to before the machine's rte.vars.mk inclusion to make
> > > correct CC available for the cross compile case.
> > > 
> > > Signed-off-by: Jerin Jacob <jerinj@marvell.com>
> > > Signed-off-by: Pavan Nikhilesh <pbhagavatula@marvell.com>
> > > ---
> > > --- /dev/null
> > > +++ b/mk/rte.helper.mk
> > > @@ -0,0 +1,12 @@
> > > +# SPDX-License-Identifier: BSD-3-Clause
> > > +# Copyright(c) 2018 Marvell International Ltd
> > > +
> > > +# rte_cc_has_argument
> > > +# Usage: MACHINE_CFLAGS += $(call rte_cc_has_argument, -mno-
> > > avx512f)
> > > +# Return the argument if the argument is supported by the
> > > compiler.
> > > +#
> > > +define rte_cc_has_argument
> > > +	$(shell $(CC) -Werror $(1) -c -x c /dev/null -o tmp$$ 2>
> > > /dev/null && rm -f tmp$$ && echo $(1) | xargs echo -n)
> > > +endef
> > 
> > What is tmp$$ ?
> 
> It is created per process with pid value.

I see. The file is in current directory with name tmp + PID.

> > If the command is interrupted in the middle, temp file is not
> > cleaned.
> 
> Yes. I think we can move to RTE_OUTPUT. Even it is not cleaned 
> then it is file, I think, that would be easiest solution.
> 
> > We could fix it with "trap".
> 
> Can we do it in Makefile? 

Yes, it is just one more command separated with ;

> > Is it possible to just avoid creating a temporary file?
> 
> I tried it but gcc creates one.

It does not create a file in my test.

A better command is:
	$(CC) -E $(1) -xc /dev/null >/dev/null
Then you can just check the return value.

If you want rte_cc_has_argument returns a string or empty as true/false,
you can do this:
	$(CC) -E $(1) -xc /dev/null >/dev/null && echo $(1)