On 30.04.21 10:03, David Brown wrote: > On 29/04/2021 21:43, Ian Molton wrote: > > Hi, > > > > I'm attempting to build my project, which does not use libc, or libm, > > but I do want to link with libgcc. > > > > additionally, I don't want any startup code to be linked - the project > > is intended to be fully standalone. > > > > If you don't use any functions from these libraries, nothing from them > will be linked into your project - it doesn't matter if the linker has them.
Still dabbling a little with AVR once in a while, I add -nostartfiles to Ian's -nostdlib, to avoid startup code. As my most recent dabble is -mmcu=attiny2313, with only 1k instructions, any extraneous code bytes would quickly be noticed. As for libm, I've always had to -lm that explicitly when needed. And for libgcc, my makefile remembers better than I, a choice to use avr-gcc, not just avr-ld for linking on a project which needed libgcc. That residual choice in the attiny2313 project confirms David's reminder that stuff is only linked if you use it. Erik makefile: ========= # vim:noexpandtab list foldmethod=manual INC_DIR=include OBJDIR=obj CC = avr-gcc CFLAGS = -g -O2 -nostartfiles -nostdlib -mmcu=attiny2313 -DMCU=attiny2313 AS = /usr/local/avr/bin/avr-as ASFLAGS = -gstabs -mmcu=attiny2313 LD = /usr/local/avr/bin/avr-ld # Let avr-gcc link, so it can find libgcc.a: LDFLAGS = -Wl,-M .SUFFIXES : .SUFFIXES : .c .h .o .s .S %.o: %.c $(CC) -c $(CFLAGS) -o $(OBJDIR)/$@ $< %.o: %.s $(AS) -I$(INC_DIR) $(ASFLAGS) -o $(OBJDIR)/$@ $< %.o: %.S $(CC) -c -I$(INC_DIR) -x assembler-with-cpp $(CFLAGS) -Wa,-alms=$(OBJDIR)/$@.lst -o $(OBJDIR)/$@ $< dimmer: init.o os.o timer.o lamps.o eeprom.o serial.o comms.o ( cd $(OBJDIR) ; $(CC) $(LDFLAGS) $(CFLAGS) -o $@.elf $^ > map ) avr-objcopy -O srec obj/dimmer.elf -S -R .eeprom --gap-fill=0xff obj/flash.srec avr-objcopy -O ihex obj/dimmer.elf -S -j .eeprom --gap-fill=0xff obj/eeprom.ihex avr-objdump -D obj/$@.elf > obj/dimmer.dump load: avrdude -P /dev/ttyUSB0 -p t2313 -c stk500 -e -U flash:w:obj/flash.srec -U eeprom:w:obj/eeprom.ihex
