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 --- arch/m68k/Makefile | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/arch/m68k/Makefile b/arch/m68k/Makefile index 997c9f20ea0f..0a99c276d9a4 100644 --- a/arch/m68k/Makefile +++ b/arch/m68k/Makefile @@ -58,7 +58,8 @@ 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) + ifdef CONFIG_MMU # without -fno-strength-reduce the 53c7xx.c driver fails ;-( KBUILD_CFLAGS += -fno-strength-reduce -ffixed-a2 @@ -69,6 +70,8 @@ KBUILD_CFLAGS += -D__uClinux__ KBUILD_AFLAGS += -D__uClinux__ endif
+KBUILD_CFLAGS += -pipe -ffreestanding + KBUILD_LDFLAGS := -m m68kelf KBUILD_LDFLAGS_MODULE += -T $(srctree)/arch/m68k/kernel/module.lds