[PATCH] Use -fno-unit-at-a-time if gcc supports it

From: Andi Kleen <ak@muc.de>
To: torvalds@osdl.org, akpm@osdl.org, rth@redhat.com,
	linux-kernel@vger.kernel.org, jh@suse.cz
Subject: [PATCH] Use -fno-unit-at-a-time if gcc supports it
Date: Fri, 5 Sep 2003 02:47:10 +0200	[thread overview]
Message-ID: <20030905004710.GA31000@averell> (raw)


Hallo,

gcc 3.4 current has switched to default -fno-unit-at-a-time mode for -O2. 
The 3.3-Hammer branch compiler used in some distributions also does this.

Unfortunately the kernel doesn't compile with unit-at-a-time currently,
it cannot tolerate the reordering of functions in relation to inline
assembly.

This patch just turns it off when gcc supports the option.

I only did it for i386 for now. The problem is actually not i386 specific
(other architectures break too), so it may make sense to move the check_gcc 
stuff into the main Makefile and do it for everybody.

-Andi

--- linux-2.6.0test4-work/arch/i386/Makefile-o	2003-08-23 13:03:08.000000000 +0200
+++ linux-2.6.0test4-work/arch/i386/Makefile	2003-09-05 02:14:07.000000000 +0200
@@ -26,6 +26,10 @@
 # prevent gcc from keeping the stack 16 byte aligned
 CFLAGS += $(call check_gcc,-mpreferred-stack-boundary=2,)
 
+# gcc 3.4/3.3-hammer support -funit-at-a-time mode, but the Kernel is not ready
+# for it yet
+CFLAGS += $(call check_gcc,-fno-unit-at-a-time,)
+
 align := $(subst -functions=0,,$(call check_gcc,-falign-functions=0,-malign-functions=0))
 
 cflags-$(CONFIG_M386)		+= -march=i386
