squash introduce ILINK, ILINKFLAGS

Makefile.base

@@ -67,8 +67,15 @@ $(BINDIR)/$(MODULE)/:
 
 $(BINDIR)/$(MODULE).o $(OBJ): | $(BINDIR)/$(MODULE)/
 
-$(BINDIR)/$(MODULE).o: $(OBJ) | ${DIRS:%=ALL--%}
-	$(Q)[ -z '$^' ] || $(LD) -r -o $@ $^
+# An empty object file is included in the link to avoid situations where modules
+# do not provide any code (e.g. sys, some boards), causing the build to fail
+# with a missing object file.
+EMPTYOBJ = $(BINDIR)/$(MODULE)/.empty.o
+$(EMPTYOBJ): | $(BINDIR)/$(MODULE)/
+	$(Q)$(CC) $(CFLAGS) -Wno-pedantic -xc -o $@ -c - < /dev/null
+
+$(BINDIR)/$(MODULE).o: $(OBJ) $(EMPTYOBJ) | ${DIRS:%=ALL--%}
+	$(Q)$(ILINK) $(ILINKFLAGS) -o $@ $^
 
 CXXFLAGS = $(filter-out $(CXXUWFLAGS), $(CFLAGS)) $(CXXEXFLAGS)
 CCASFLAGS = $(filter-out $(CCASUWFLAGS), $(CFLAGS)) $(CCASEXFLAGS)

boards/native/Makefile.include

@@ -72,6 +72,7 @@ export CXXEXFLAGS +=
 
 ifeq ($(shell uname -m),x86_64)
   export LINKFLAGS += -m32
+  export ILINKFLAGS += -r -m elf_i386
 endif
 ifeq ($(shell uname -s),FreeBSD)
   ifeq ($(shell uname -m),amd64)

cpu/atmega1281/Makefile.include

@@ -1,6 +1,9 @@
 # tell the build system that the CPU depends on the atmega common files
 USEMODULE += atmega_common
 
+# CPU family, see https://gcc.gnu.org/onlinedocs/gcc/AVR-Options.html
+export CPU_FAM = avr51
+
 # define path to atmega common module, which is needed for this CPU
 export ATMEGA_COMMON = $(RIOTCPU)/atmega_common/
 

cpu/atmega2560/Makefile.include

@@ -1,6 +1,9 @@
 # tell the build system that the CPU depends on the atmega common files
 USEMODULE += atmega_common
 
+# CPU family, see https://gcc.gnu.org/onlinedocs/gcc/AVR-Options.html
+export CPU_FAM = avr6
+
 # define path to atmega common module, which is needed for this CPU
 export ATMEGA_COMMON = $(RIOTCPU)/atmega_common/
 

cpu/atmega328p/Makefile.include

@@ -1,6 +1,9 @@
 # tell the build system that the CPU depends on the atmega common files
 USEMODULE += atmega_common
 
+# CPU family, see https://gcc.gnu.org/onlinedocs/gcc/AVR-Options.html
+export CPU_FAM = avr5
+
 # define path to atmega common module, which is needed for this CPU
 export ATMEGA_COMMON = $(RIOTCPU)/atmega_common/
 

cpu/atmega_common/Makefile.include

@@ -8,6 +8,9 @@ export CFLAGS_OPT  ?= -Os
 
 export CFLAGS += $(CFLAGS_CPU) $(CFLAGS_LINK) $(CFLAGS_DBG) $(CFLAGS_OPT)
 export ASFLAGS += $(CFLAGS_CPU) $(CFLAGS_DBG)
+# See https://gcc.gnu.org/onlinedocs/gcc/AVR-Options.html for information on
+# which CPU_FAM corresponds to your CPU
+export ILINKFLAGS += -r -m $(CPU_FAM)
 export LINKFLAGS += $(CFLAGS_CPU) $(CFLAGS_DBG) $(CFLAGS_OPT) -static -lgcc -e reset_handler -Wl,--gc-sections
 
 # export the peripheral drivers to be linked into the final binary

makefiles/toolchain/gnu.inc.mk

@@ -8,6 +8,8 @@ export AR         = $(PREFIX)ar
 endif
 export AS         = $(PREFIX)as
 export LD         = $(PREFIX)ld
+export ILINK      = $(LD)
+export ILINKFLAGS ?= -r
 export LINK       = $(PREFIX)gcc
 export LINKXX     = $(PREFIX)g++
 export SIZE       = $(PREFIX)size

makefiles/toolchain/llvm.inc.mk

@@ -17,6 +17,8 @@ export NM          = $(LLVMPREFIX)nm
 # `makefiles/libc/newlib.mk` are not supported. Therefore
 # we just use GCC for now.
 export LD          = $(PREFIX)ld
+export ILINK       = $(LD)
+export ILINKFLAGS ?= -r
 export LINK        = $(PREFIX)gcc
 export LINKXX      = $(PREFIX)g++
 # objcopy does not have a clear substitute in LLVM, use GNU binutils

makefiles/vars.inc.mk

@@ -47,6 +47,8 @@ export AR                    # The command to create the object file archives.
 export ARFLAGS               # Command-line options to pass to AR, default `rcs`.
 export AS                    # The assembler.
 export ASFLAGS               # Flags for the assembler.
+export ILINK                 # Command used to perform incremental linking to create intermediate object files. Usually "ld"
+export ILINKFLAGS            # Incremental link command line options.
 export LINK                  # The command used to link the files. Must take the same parameters as GCC, i.e. "ld" won't work.
 export LINKFLAGS             # Flags to supply in the linking step.
 export LTOFLAGS              # extra CFLAGS for compiling with link time optimization