m68k: Add -ffreestanding to CFLAGS

This patch fixes a build failure when using GCC 8.1:

/usr/bin/ld: block/partitions/ldm.o: in function `ldm_parse_tocblock':
block/partitions/ldm.c:153: undefined reference to `strcmp'

This is caused by a new optimization which effectively replaces a
strncmp() call with a strcmp() call. This affects a number of strncmp()
call sites in the kernel.

The entire class of optimizations is avoided with -fno-builtin, which
gets enabled by -ffreestanding. This may avoid possible future build
failures in case new optimizations appear in future compilers.

I haven't done any performance measurements with this patch but I did
count the function calls in a defconfig build. For example, there are now
23 more sprintf() calls and 39 fewer strcpy() calls. The effect on the
other libc functions is smaller.

If this harms performance we can tackle that regression by optimizing
the call sites, ideally using semantic patches. That way, clang and ICC
builds might benfit too.

Cc: stable@vger.kernel.org
Reference: https://marc.info/?l=linux-m68k&m=154514816222244&w=2
Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

diff --git a/arch/m68k/Makefile b/arch/m68k/Makefile
index f00ca53f8c1417e7699eec4135b632cced5c47a0..482513b9af2c5dde54d28e19df519886b56b4fca 100644 (file)
--- a/arch/m68k/Makefile
+++ b/arch/m68k/Makefile
@@ -58,7 +58,10 @@ cpuflags-$(CONFIG_M5206e)    := $(call cc-option,-mcpu=5206e,-m5200)
 cpuflags-$(CONFIG_M5206)       := $(call cc-option,-mcpu=5206,-m5200)
 
 KBUILD_AFLAGS += $(cpuflags-y)
-KBUILD_CFLAGS += $(cpuflags-y) -pipe
+KBUILD_CFLAGS += $(cpuflags-y)
+
+KBUILD_CFLAGS += -pipe -ffreestanding
+
 ifdef CONFIG_MMU
 # without -fno-strength-reduce the 53c7xx.c driver fails ;-(
 KBUILD_CFLAGS += -fno-strength-reduce -ffixed-a2