sh: Fix FPU tuning on toolchains with mismatched multilib targets. (8a2fd5f3) · Commits · 戴 / test

Presently there is very little standing in the way of using an SH-4 toolchain for building an SH-2 kernel, and vice versa. Binutils itself has no limitations whatsoever and supports explicit ISA hinting, which we already use with varying degrees of success today. This leaves GCC as the odd one out, due to a rather dubious policy decision by the GCC folks to not include all of the CPU family variants in the default list of multilib targets in GCC4. Despite best efforts to the contrary, libgcc itself already contains awareness of the various CPU types and remains generally usable, allowing it to safely be referenced even on a mismatched target (and indeed, explicit ISA tuning by binutils keeps us honest in terms of ensuring that we do not link incompatible objects in). In order to support this, a couple of changes had to be made. Firstly, the introduction of MAYBE_DECLARE_EXPORT(), which provides a __weak extern reference for libgcc resident routines when finer-grained -m<cpu-family> based tuning is not supported by the toolchain. This fixes up the __sdivsi3_i4i and __udivsi3_i4i references when dealing with SH-2 kernels linked with an SH-4 libgcc. Secondly, in case where we are unable to find a suitable match for CPU family tuning but still have a toolchain that defaults to FP instruction generation, a suitable nofpu target must be selected. This is accomplished by selecting the first nofpu multilib target supported by the toolchain, which is also necessary for selecting the proper libgcc to link against. Signed-off-by:

Paul Mundt <lethal@linux-sh.org>

arch/sh/Makefile

+16 −0

Original line number	Diff line number	Diff line
		@@ -38,6 +38,22 @@ cflags-$(CONFIG_CPU_SH4A) += $(call cc-option,-m4a,) \
		$(call cc-option,-m4a-nofpu,)
		cflags-$(CONFIG_CPU_SH5) := $(call cc-option,-m5-32media-nofpu,)

		ifeq ($(cflags-y),)
		#
		# In the case where we are stuck with a compiler that has been uselessly
		# restricted to a particular ISA, a favourite default of newer GCCs when
		# extensive multilib targets are not provided, ensure we get the best fit
		# regarding FP generation. This is necessary to avoid references to FP
		# variants in libgcc where integer variants exist, which otherwise result
		# in link errors. This is intentionally stupid (albeit many orders of
		# magnitude less than GCC's default behaviour), as anything with a large
		# number of multilib targets better have been built correctly for
		# the target in mind.
		#
		cflags-y += $(shell $(CC) $(KBUILD_CFLAGS) -print-multi-lib \| \
		grep nofpu \| sed q \| sed -e 's/^/-/;s/;.*$$//')
		endif

		cflags-$(CONFIG_CPU_BIG_ENDIAN) += -mb
		cflags-$(CONFIG_CPU_LITTLE_ENDIAN) += -ml

arch/sh/kernel/sh_ksyms_32.c

+6 −5

Original line number	Diff line number	Diff line
		@@ -50,7 +50,10 @@ EXPORT_SYMBOL(__udelay);
		EXPORT_SYMBOL(__ndelay);
		EXPORT_SYMBOL(__const_udelay);

		#define DECLARE_EXPORT(name) extern void name(void);EXPORT_SYMBOL(name)
		#define DECLARE_EXPORT(name) \
		extern void name(void);EXPORT_SYMBOL(name)
		#define MAYBE_DECLARE_EXPORT(name) \
		extern void name(void) __weak;EXPORT_SYMBOL(name)

		/* These symbols are generated by the compiler itself */
		DECLARE_EXPORT(__udivsi3);
		@@ -109,10 +112,8 @@ DECLARE_EXPORT(__movmemSI12_i4);
		* compiler which include backported patches.
		*/
		DECLARE_EXPORT(__udiv_qrnnd_16);
		#if !defined(CONFIG_CPU_SH2)
		DECLARE_EXPORT(__sdivsi3_i4i);
		DECLARE_EXPORT(__udivsi3_i4i);
		#endif
		MAYBE_DECLARE_EXPORT(__sdivsi3_i4i);
		MAYBE_DECLARE_EXPORT(__udivsi3_i4i);
		#endif
		#else /* GCC 3.x */
		DECLARE_EXPORT(__movstr_i4_even);

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