nios2: set appropriate compiler flags for math support

Nios II CPUs vary in configuration on whether they support
'mul', 'mulx', and 'div' family of instructions. The compiler
can be told to use GCC integer library routines instead if
needed.

Ideally we would just pull the configuration out of system.h,
but pulling include file #defines into the Make environment
will involve some build system work that is best left to a
later improvement.

We've decided to take this build-time approach rather than
handle unimplemented instruction exceptions, so remove the
hook in exception.S

Change-Id: I05be0d5ed4c1a49b23dca1550ee66fd5891044d2
Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>

arch/nios2/Kconfig

@@ -55,6 +55,18 @@ config IRQ_OFFLOAD
 	Enable irq_offload() API which allows functions to be synchronously
 	run in interrupt context. Mainly useful for test cases.
 
+config HAS_MUL_INSTRUCTION
+	bool
+	default n
+
+config HAS_DIV_INSTRUCTION
+	bool
+	default n
+
+config HAS_MULX_INSTRUCTION
+	bool
+	default n
+
 endmenu
 
 source "arch/nios2/soc/*/Kconfig"

arch/nios2/Makefile

@@ -9,6 +9,24 @@ arch_cflags := $(call cc-option,-G0)
 arch_cflags += $(call cc-option,-ffunction-sections) \
 	       $(call cc-option,-fdata-sections)
 
+# TODO Find a way to pull this out of system.h somehow
+# instead of having Kconfig for it
+ifdef CONFIG_HAS_MUL_INSTRUCTION
+arch_cflags += -mhw-mul
+else
+arch_cflags += -mno-hw-mul
+endif
+ifdef CONFIG_HAS_MULX_INSTRUCTION
+arch_cflags += -mhw-mulx
+else
+arch_cflags += -mno-hw-mulx
+endif
+ifdef CONFIG_HAS_DIV_INSTRUCTION
+arch_cflags += -mhw-div
+else
+arch_cflags += -mno-hw-div
+endif
+
 # Nios II CPUs are configurable and we need to pull in the generated
 # headers system.h and linker.h which specify what is enabled and where
 # everything is.

arch/nios2/core/exception.S

@@ -26,7 +26,6 @@ GTEXT(_exception_enter_fault)
 /* import */
 GTEXT(_Fault)
 GTEXT(_Swap)
-GTEXT(_exception_try_muldiv)
 #ifdef CONFIG_IRQ_OFFLOAD
 GTEXT(_irq_do_offload)
 GTEXT(_offload_routine)
@@ -189,15 +188,6 @@ BRANCH_LABEL(not_interrupt)
 	bne   r11, zero, is_interrupt
 #endif
 
-#if 0 /* TODO: implement multiply/divide handling */
-	/* Could be an unimplemented instruction we have to emulate.
-	 * Smaller Nios II cores don't have multiply or divide instructions.
-	 * This code comes back to either _exception_enter_fault or
-	 * _exception_exit
-	 */
-	jmpi _exception_try_muldiv
-#endif
-
 SECTION_FUNC(exception.entry, _exception_enter_fault)
 	/* If we get here, the exception wasn't in interrupt or an
 	 * unimplemented math instruction. Let _Fault() handle it in

arch/nios2/soc/nios2-qemu/Kconfig.soc

@@ -1,3 +1,6 @@
 config SOC_NIOS2_QEMU
 	bool "Nios II - Experimental QEMU emulation"
+	select HAS_MUL_INSTRUCTION
+	select HAS_DIV_INSTRUCTION
+	select HAS_MULX_INSTRUCTION
 

arch/nios2/soc/nios2f-zephyr/Kconfig.soc

@@ -1,3 +1,5 @@
 config SOC_NIOS2F_ZEPHYR
 	bool "Nios IIf - Zephyr Golden Configuration"
+	select HAS_MUL_INSTRUCTION
+	select HAS_DIV_INSTRUCTION