m68k: Use kernel's generic muldi3 libgcc function

Use the kernels own generic lib/muldi3.c implementation of muldi3 for
68K machines. Some 68K CPUs support 64bit multiplies so move the arch
specific umul_ppmm() macro into a header file that is included by
lib/muldi3.c. That way it can take advantage of the single instruction
when available.

There does not appear to be any existing mechanism for the generic
lib/muldi3.c code to pick up an external arch definition of umul_ppmm().
Create an arch specific libgcc.h that can optionally be included by
the system include/linux/libgcc.h to allow for this.

Somewhat oddly there is also a similar definition of umul_ppmm() in
the non-architecture code in lib/crypto/mpi/longlong.h for a wide range
or machines. Its presence ends up complicating the include setup and
means not being able to use something like compiler.h instead. Actually
there is a few other defines of umul_ppmm() macros spread around in
various architectures, but not directly usable for the m68k case.

Signed-off-by: Greg Ungerer <[email protected]>
Link: https://lore.kernel.org/[email protected]
Reviewed-by: Geert Uytterhoeven <[email protected]>
Reviewed-by: Arnd Bergmann <[email protected]>
Signed-off-by: Geert Uytterhoeven <[email protected]>

Author: Greg Ungerer

arch/Kconfig

@@ -1526,6 +1526,14 @@ config HAVE_ARCH_COMPILER_H
 	  linux/compiler-*.h in order to override macro definitions that those
 	  headers generally provide.
 
+config HAVE_ARCH_LIBGCC_H
+	bool
+	help
+	  An architecture can select this if it provides an
+	  asm/libgcc.h header that should be included after
+	  linux/libgcc.h in order to override macro definitions that
+	  header generally provides.
+
 config HAVE_ARCH_PREL32_RELOCATIONS
 	bool
 	help

arch/m68k/Kconfig

@@ -23,7 +23,9 @@ config M68K
 	select GENERIC_LIB_ASHLDI3
 	select GENERIC_LIB_ASHRDI3
 	select GENERIC_LIB_LSHRDI3
+	select GENERIC_LIB_MULDI3
 	select HAS_IOPORT if PCI || ISA || ATARI_ROM_ISA
+	select HAVE_ARCH_LIBGCC_H
 	select HAVE_ARCH_SECCOMP
 	select HAVE_ARCH_SECCOMP_FILTER
 	select HAVE_ASM_MODVERSIONS

arch/m68k/include/asm/libgcc.h

@@ -0,0 +1,20 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_M68K_LIBGCC_H
+#define __ASM_M68K_LIBGCC_H
+
+#ifndef CONFIG_CPU_HAS_NO_MULDIV64
+/*
+ * For those 68K CPUs that support 64bit multiply define umul_ppm()
+ * for the common muldi3 libgcc helper function (in lib/muldi3.c).
+ * CPUs that don't have it (like the original 68000 and ColdFire)
+ * will fallback to using the C-coded version of umul_ppmm().
+ */
+#define umul_ppmm(w1, w0, u, v)				\
+	__asm__ ("mulu%.l %3,%1:%0"			\
+		 : "=d" ((unsigned long)(w0)),		\
+		   "=d" ((unsigned long)(w1))		\
+		 : "%0" ((unsigned long)(u)),		\
+		   "dmi" ((unsigned long)(v)))
+#endif /* !CONFIG_CPU_HAS_NO_MULDIV64 */
+
+#endif /* __ASM_M68K_LIBGCC_H */

arch/m68k/lib/Makefile

@@ -4,7 +4,7 @@
 # Makefile for m68k-specific library files..
 #
 
-lib-y	:= muldi3.o memcpy.o memset.o memmove.o
+lib-y	:= memcpy.o memset.o memmove.o
 
 lib-$(CONFIG_MMU) += uaccess.o
 lib-$(CONFIG_CPU_HAS_NO_MULDIV64) += mulsi3.o divsi3.o udivsi3.o

arch/m68k/lib/muldi3.c

@@ -34,4 +34,8 @@ long long notrace __lshrdi3(long long u, word_type b);
 long long notrace __muldi3(long long u, long long v);
 word_type notrace __ucmpdi2(unsigned long long a, unsigned long long b);
 
+#ifdef CONFIG_HAVE_ARCH_LIBGCC_H
+#include <asm/libgcc.h>
+#endif
+
 #endif /* __ASM_LIBGCC_H */