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From: Peter Maydell <peter.maydell@linaro.org>
Date: Wed, 15 Jan 2014 19:35:12 +0000
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Subject: Re: [Qemu-devel] [PATCH v16 2/9] rules.mak: allow per object cflags
	and libs
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To: Fam Zheng <famz@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Stefan Hajnoczi <stefanha@redhat.com>, Michael Tokarev <mjt@tls.msk.ru>, QEMU Developers <qemu-devel@nongnu.org>, Alex Bligh <alex@alex.org.uk>, Paolo Bonzini <pbonzini@redhat.com>, Miroslav Rezanina <mrezanin@redhat.com>, =?UTF-8?Q?Llu=C3=ADs_Vilanova?= <vilanova@ac.upc.edu>, Richard Henderson <rth@twiddle.net>

On 15 January 2014 08:48, Fam Zheng <famz@redhat.com> wrote:
> Adds extract-libs in LINK to expand any "per object libs", the syntax to define
> such a libs options is like:
>
>         foo.o-libs := $(CURL_LIBS)
>
> in block/Makefile.objs.
>
> Similarly,
>
>         foo.o-cflags := $(FOO_CFLAGS)
>
> is also supported.
>
> "foo.o" must be listed in a nested var (e.g. common-obj-y) to make the
> option variables effective.
>
> Signed-off-by: Fam Zheng <famz@redhat.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  rules.mak | 19 ++++++++++++++++---
>  1 file changed, 16 insertions(+), 3 deletions(-)
>
> diff --git a/rules.mak b/rules.mak
> index 7d27602..9398268 100644
> --- a/rules.mak
> +++ b/rules.mak
> @@ -21,15 +21,17 @@ QEMU_DGFLAGS += -MMD -MP -MT $@ -MF $(*D)/$(*F).d
>  # Same as -I$(SRC_PATH) -I., but for the nested source/object directories
>  QEMU_INCLUDES += -I$(<D) -I$(@D)
>
> +extract-libs = $(strip $(foreach o,$1,$($o-libs)))
> +
>  %.o: %.c
> -       $(call quiet-command,$(CC) $(QEMU_INCLUDES) $(QEMU_CFLAGS) $(QEMU_DGFLAGS) $(CFLAGS) -c -o $@ $<,"  CC    $(TARGET_DIR)$@")
> +       $(call quiet-command,$(CC) $(QEMU_INCLUDES) $(QEMU_CFLAGS) $(QEMU_DGFLAGS) $(CFLAGS) $($@-cflags) -c -o $@ $<,"  CC    $(TARGET_DIR)$@")

Shouldn't this change also be made in the rules for compiling
.cpp and .m files (which also use CFLAGS and could benefit
from per-object flags) ?

(For instance it would be nice if I could compile the libvixl
C++ sources with a different set of flags.)

thanks
-- PMM