Re: [PATCH] tools/virtio: fix build break for aarch64

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Mar 22, 2023 at 03:59:45PM +0800, Peng Fan (OSS) wrote:
> From: Peng Fan <peng.fan@nxp.com>
> 
> "-mfunction-return=thunk -mindirect-branch-register" are only valid
> for x86. So introduce compiler operation check to avoid such issues
> 
> Fixes: 0d0ed4006127 ("tools/virtio: enable to build with retpoline")
> Signed-off-by: Peng Fan <peng.fan@nxp.com>
> ---
>  tools/virtio/Makefile | 21 ++++++++++++++++++++-
>  1 file changed, 20 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/virtio/Makefile b/tools/virtio/Makefile
> index 7b7139d97d74..1a9e1be52e4f 100644
> --- a/tools/virtio/Makefile
> +++ b/tools/virtio/Makefile
> @@ -4,7 +4,26 @@ test: virtio_test vringh_test
>  virtio_test: virtio_ring.o virtio_test.o
>  vringh_test: vringh_test.o vringh.o virtio_ring.o
>  
> -CFLAGS += -g -O2 -Werror -Wno-maybe-uninitialized -Wall -I. -I../include/ -I ../../usr/include/ -Wno-pointer-sign -fno-strict-overflow -fno-strict-aliasing -fno-common -MMD -U_FORTIFY_SOURCE -include ../../include/linux/kconfig.h -mfunction-return=thunk -fcf-protection=none -mindirect-branch-register
> +TMPOUT = .tmp_$$$$

if you are going to do this pls use mktemp.
But I don't see why not just use -o /dev/null

> +try-run = $(shell set -e;		\
> +	TMP=$(TMPOUT)/tmp;		\
> +	trap "rm -rf $(TMPOUT)" EXIT;	\
> +	mkdir -p $(TMPOUT);		\
> +	if ($(1)) >/dev/null 2>&1;	\
> +	then echo "$(2)";		\
> +	else echo "$(3)";		\
> +	fi)
> +
> +__cc-option = $(call try-run,\
> +	$(1) -Werror $(2) -c -x c /dev/null -o "$$TMP",$(2),)
> +cc-option = $(call __cc-option, $(CC),$(1))
> +
> +CFLAGS += -g -O2 -Werror -Wno-maybe-uninitialized -Wall -I. -I../include/ -I ../../usr/include/ -Wno-pointer-sign -fno-strict-overflow -fno-strict-aliasing -fno-common -MMD -U_FORTIFY_SOURCE -include ../../include/linux/kconfig.h
> +
> +CFLAGS += $(call cc-option,-mfunction-return=thunk)
> +CFLAGS += $(call cc-option,-fcf-protection=none)
> +CFLAGS += $(call cc-option,-mindirect-branch-register)
> +

As far as I can tell this will do the dance with the empty input
each time CFLAGS is evaluated.

Which seems unnecessarily baroque - just use ":=" and it will
be evaluated once.


>  CFLAGS += -pthread
>  LDFLAGS += -pthread
>  vpath %.c ../../drivers/virtio ../../drivers/vhost
> -- 
> 2.37.1