cpu/mips: Integrate better with RIOT newlib layer

- Copied the relevant parts of mipshal.mk from the toolchain
 - Cleaned up CFLAGS and more in Makefile.include
 - Added empty syscalls implementation which can be used to interface
   with the UHI system
 - Added a note on why -std=gnu99 is necessary for this CPU presently

cpu/mips32r2_common/Makefile

@@ -1,4 +1,4 @@
 MODULE = cpu
-DIRS = periph
+DIRS = periph newlib_syscalls_mips_uhi
 
 include $(RIOTBASE)/Makefile.base

cpu/mips32r2_common/Makefile.include

@@ -6,3 +6,5 @@ include $(RIOTMAKE)/arch/mips.inc.mk
 
 export LINKFLAGS += -Tuhi32.ld
 export USEMODULE += periph
+export USEMODULE += newlib
+export USEMODULE += newlib_syscalls_mips_uhi

cpu/mips32r2_common/cpu.c

@@ -60,10 +60,6 @@ void mips_start(void)
 {
     board_init();
 
-#if MODULE_NEWLIB
-#error "This Port is designed to work with the (newlib) C library provided with the mips sdk toolchain"
-#endif
-
     /* kernel_init */
     kernel_init();
 }

cpu/mips32r2_common/newlib_syscalls_mips_uhi/Makefile

@@ -0,0 +1 @@
+include $(RIOTBASE)/Makefile.base

cpu/mips32r2_common/newlib_syscalls_mips_uhi/syscalls.c

@@ -0,0 +1,11 @@
+/*
+ * Copyright (C) 2017 whoever implements this
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+/**
+ * @todo Here there should be a syscall implementation for use with the mips-mti-elf toolchain newlib
+ */
+typedef int dont_be_pedantic;

cpu/mips_pic32mx/Makefile.include

@@ -12,7 +12,7 @@ export CFLAGS += -march=m4k -DSKIP_COPY_TO_RAM
 export USEMODULE += periph
 
 export LINKFLAGS += -Wl,--defsym,__use_excpt_boot=0 $(CFLAGS)
-export LINKFLAGS += -T$(RIOTCPU)/$(CPU)/ldscripts/pic32mx512_12_128_uhi.ld
+export LINKFLAGS += -Tpic32mx512_12_128_uhi.ld
 
 # the pickit programmer (MPLAB-IPE) wants physical addresses in the hex file!!
 export OBJCOPY = objcopy #use system objcopy as toolchain one is broken.

cpu/mips_pic32mz/Makefile.include

@@ -13,7 +13,7 @@ export CFLAGS += -DMIPS_MICROMIPS
 export USEMODULE += periph
 
 export LINKFLAGS += -Wl,--defsym,__use_excpt_boot=0 $(CFLAGS)
-export LINKFLAGS += -T$(RIOTCPU)/$(CPU)/ldscripts/pic32mz2048_uhi.ld
+export LINKFLAGS += -Tpic32mz2048_uhi.ld
 
 # the pickit programmer (MPLAB-IPE) wants physical addresses in the hex file!!
 export OBJCOPY = objcopy #use system objcopy as toolchain one is broken.

makefiles/arch/mips.inc.mk

@@ -1,31 +1,47 @@
-ifndef MIPS_ELF_ROOT
-ifneq ($(BUILD_IN_DOCKER),1) #Don't error when BUILD_IN_DOCKER=1 as it _is_ set in DOCKER
-    $(error "Please set $$(MIPS_ELF_ROOT) and ensure $$(MIPS_ELF_ROOT)/bin is on your PATH")
-endif
-endif
-
 # Target triple for the build.
 export TARGET_ARCH ?= mips-mti-elf
 
 export ABI=32
 
-ifneq ($(BUILD_IN_DOCKER),1) #Don't error when BUILD_IN_DOCKER=1 as MIPS_ELF_ROOT _is_ set in DOCKER
-include $(MIPS_ELF_ROOT)/share/mips/rules/mipshal.mk
-endif
+# Portable 'lowercase' func.
+lc = $(subst A,a,$(subst B,b,$(subst C,c,$(subst D,d,$(subst E,e,$(subst F,f,$(subst G,g,$(subst H,h,$(subst I,i,$(subst J,j,$(subst K,k,$(subst L,l,$(subst M,m,$(subst N,n,$(subst O,o,$(subst P,p,$(subst Q,q,$(subst R,r,$(subst S,s,$(subst T,t,$(subst U,u,$(subst V,v,$(subst W,w,$(subst X,x,$(subst Y,y,$(subst Z,z,$1))))))))))))))))))))))))))
+
+# Default values for the linker script symbols listed below are
+# defined in the linker script.
+
+# These are linker script symbols that are prefixed with '__"
+priv_symbols = MEMORY_BASE MEMORY_SIZE STACK
+priv_symbols += ENABLE_XPA
+priv_symbols += FLUSH_TO_ZERO
+priv_symbols += FLASH_START APP_START FLASH_APP_START
+priv_symbols += ISR_VEC_SPACE ISR_VECTOR_COUNT
+
+comma := ,
+
+# A bit of makefile magic:
+# foreach symbol in overridable ld-symbols :
+#   If symbol has a value, produce a linker argument for that symbol.
+MIPS_HAL_LDFLAGS = $(foreach a,$(priv_symbols),$(if $($a),-Wl$(comma)--defsym$(comma)__$(call lc,$(a))=$($a)))
 
 # define build specific options
-export CFLAGS_CPU   = -EL -std=gnu99
+# Remove -std=gnu99 once the MIPS toolchain headers are updated to include upstream
+# newlib commit 81c17949f0419d1c4fee421c60987ea1149522ae
+# https://cygwin.com/git/gitweb.cgi?p=newlib-cygwin.git;a=commitdiff;h=81c17949f0419d1c4fee421c60987ea1149522ae
+# Otherwise we get an error about a missing declaration of strnlen in some parts.
+export CFLAGS += -std=gnu99
+export CFLAGS_CPU   = -EL -mabi=$(ABI)
+# Why not -fdata-sections?? /JN
 export CFLAGS_LINK  = -ffunction-sections -fno-builtin -fshort-enums #-fdata-sections
-export CFLAGS_DBG = -O0 -g2
-export CFLAGS_OPT = -Os -g2
+export CFLAGS_DBG   = -g3
+export CFLAGS_OPT   = -Os
 
-export CFLAGS += $(CFLAGS_CPU) $(CFLAGS_LINK) $(CFLAGS_OPT)
-#$(CFLAGS_DBG)
+export CFLAGS += $(CFLAGS_CPU) $(CFLAGS_LINK) $(CFLAGS_OPT) $(CFLAGS_DBG)
 
 ifeq ($(USE_HARD_FLOAT),1)
     export CFLAGS += -mhard-float
 else
-    export CFLAGS += -msoft-float #hard-float is the default so we must set soft-float
+    #hard-float is the default so we must set soft-float
+    export CFLAGS += -msoft-float
     export LINKFLAGS += -msoft-float
 endif
 
@@ -33,9 +49,10 @@ ifeq ($(USE_DSP),1)
     export CFLAGS += -mdsp
 endif
 
-export ASFLAGS += $(CFLAGS_CPU) $(CFLAGS_OPT) #$(CFLAGS_DBG)
+export ASFLAGS += $(CFLAGS_CPU) $(CFLAGS_OPT) $(CFLAGS_DBG)
 
-export LINKFLAGS += $(MIPS_HAL_LDFLAGS) -mabi=$(ABI)
+export LINKFLAGS += $(MIPS_HAL_LDFLAGS)
+export LINKFLAGS += -L$(RIOTCPU)/$(CPU)/ldscripts
 export LINKFLAGS += $(CFLAGS_CPU) $(CFLAGS_DBG) $(CFLAGS_OPT)
 export LINKFLAGS += -Wl,--gc-sections