[PATCH 02/20] pc-bios/optionrom: detect CC options just once

[Paolo Bonzini <pbonzini@redhat.com>]

In preparation for adding Docker container support, detect compiler options
just once rather than once per Make run; container startup overhead is
substantial and doing the detection just once makes things faster.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 pc-bios/optionrom/Makefile | 37 +++++++++++++++++++++++++------------
 1 file changed, 25 insertions(+), 12 deletions(-)

diff --git a/pc-bios/optionrom/Makefile b/pc-bios/optionrom/Makefile
index 3e06c11dea..f514e4f84b 100644
--- a/pc-bios/optionrom/Makefile
+++ b/pc-bios/optionrom/Makefile
@@ -8,23 +8,33 @@ all: multiboot.bin multiboot_dma.bin linuxboot.bin linuxboot_dma.bin kvmvapic.bi
 
 CFLAGS = -O2 -g
 
+NULL :=
+SPACE := $(NULL) #
+TARGET_PREFIX := $(patsubst %/,%:$(SPACE),$(TARGET_DIR))
+
+quiet-@ = $(if $(V),,@)
 quiet-command = $(if $(V),$1,$(if $(2),@printf "  %-7s %s\n" $2 $3 && $1, @$1))
-cc-option = $(if $(shell $(CC) $1 -c -o /dev/null -xc /dev/null >/dev/null 2>&1 && echo OK), $1, $2)
-
-override CFLAGS += -march=i486 -Wall $(EXTRA_CFLAGS) -m16
-
-# If -fcf-protection is enabled in flags or compiler defaults that will
-# conflict with -march=i486
-override CFLAGS += $(call cc-option, -fcf-protection=none)
 
 # Flags for dependency generation
 override CPPFLAGS += -MMD -MP -MT $@ -MF $(@D)/$(*F).d
 
-override CFLAGS += $(call cc-option, -fno-pie)
-override CFLAGS += $(call cc-option, -no-pie)
+override CFLAGS += -march=i486 -Wall $(EXTRA_CFLAGS) -m16
 override CFLAGS += -ffreestanding -I$(TOPSRC_DIR)/include
-override CFLAGS += $(call cc-option, -fno-stack-protector)
-override CFLAGS += $(call cc-option, -Wno-array-bounds)
+
+cc-test = $(CC) -Werror $1 -c -o /dev/null -xc /dev/null >/dev/null 2>/dev/null
+cc-option = if $(call cc-test, $1); then \
+    echo "$(TARGET_PREFIX)$1 detected" && echo "override CFLAGS += $1" >&3; else \
+    echo "$(TARGET_PREFIX)$1 not detected" $(if $2,&& echo "override CFLAGS += $2" >&3); fi
+
+# If -fcf-protection is enabled in flags or compiler defaults that will
+# conflict with -march=i486
+config-cc.mak: Makefile
+	$(quiet-@)($(call cc-option,-fcf-protection=none); \
+	    $(call cc-option,-fno-pie); \
+	    $(call cc-option,-no-pie); \
+	    $(call cc-option,-fno-stack-protector); \
+	    $(call cc-option,-Wno-array-bounds)) 3> config-cc.mak
+-include config-cc.mak
 
 override LDFLAGS = -nostdlib -Wl,-T,$(SRC_DIR)/flat.lds
 
@@ -50,7 +60,10 @@ include $(wildcard *.d)
 clean:
 	rm -f *.o *.d *.raw *.img *.bin *~
 
+distclean:
+	rm -f config-cc.mak
+
 # suppress auto-removal of intermediate files
 .SECONDARY:
 
-.PHONY: all clean
+.PHONY: all clean distclean
-- 
2.37.1