[PATCH] fix incorrect use of -fno-unit-at-a-time on GCC >= 4

Axel Reinhold reported wrong code being emitted for arch/i386/kernel/i8259.c
using gcc-4.2, while the same code with gcc-4.1 was valid. The problem was
tracked down to gcc-4.2 messing up with sections with this option which is
already deprecated for gcc 4.x, and the asm statements were incorrectly
assigned to section .data. It was also possible to trick gcc-4.1 into the
same error by simply declaring an array before any asm statement.

The correct fix is to remove -fno-unit-at-a-time with gcc >= 4, which is
also what has been done in 2.6. In anticipation of such other problems with
gcc 4.x, a new function "if_gcc4" has been added to the main Makefile.

Signed-off-by: Willy Tarreau <w@1wt.eu>

diff --git a/Makefile b/Makefile
index 6f23ba2..71b6652 100644 (file)
--- a/Makefile
+++ b/Makefile
@@ -100,6 +100,7 @@ endif
 AFLAGS := -D__ASSEMBLY__ $(CPPFLAGS)
 
 check_gcc = $(shell if $(CC) $(1) -S -o /dev/null -xc /dev/null > /dev/null 2>&1; then echo "$(1)"; else echo "$(2)"; fi)
+if_gcc4 = $(shell if echo __GNUC__ | $(CC) -E -xc - | grep -q '^4$$' > /dev/null 2>&1; then echo "$(1)"; else echo "$(2)"; fi)
 
 # disable pointer signedness warnings in gcc 4.0
 CFLAGS += $(call check_gcc,-Wno-pointer-sign,)

diff --git a/arch/i386/Makefile b/arch/i386/Makefile
index 8f93efd..8ba6bd0 100644 (file)
--- a/arch/i386/Makefile
+++ b/arch/i386/Makefile
@@ -92,9 +92,9 @@ ifdef CONFIG_MVIAC3_2
 CFLAGS += $(call check_gcc,-march=c3-2,-march=i686)
 endif
 
-# Disable unit-at-a-time mode, it makes gcc use a lot more stack
-# due to the lack of sharing of stacklots.
-CFLAGS += $(call check_gcc,-fno-unit-at-a-time,)
+# Disable unit-at-a-time mode on pre-gcc-4.0 compilers, it makes gcc use
+# a lot more stack due to the lack of sharing of stacklots.
+CFLAGS += $(call if_gcc4,,$(call check_gcc,-fno-unit-at-a-time,))
 
 HEAD := arch/i386/kernel/head.o arch/i386/kernel/init_task.o