Interleave Assembly and Source for avr-objdump
First make sure you add -g to all your compilation commands.

Then you can run avr-objdump -S build/spi.elf (for instance).

Also I see you're missing the MCU definition in your link command. Without that it won't link in the proper C startup routines and your program will most probably not run.

Here is a makefile I use:

PREFIX=avr-
CC=${PREFIX}gcc
CXX=${PREFIX}g++
LD=${PREFIX}ld
AS=${PREFIX}as
OBJCOPY=${PREFIX}objcopy
OBJDUMP=${PREFIX}objdump

BIN=blink
MCU=atmega328p
OBJS=blink.o

CFLAGS=-g -mmcu=${MCU} -ffunction-sections -fdata-sections
CXXFLAGS=-g -mmcu=${MCU} -ffunction-sections -fdata-sections -fno-exceptions
LDFLAGS=-mmcu=${MCU} -Wl,--gc-sections

${BIN}.hex: ${BIN}.elf
    ${OBJCOPY} -O ihex -R .eeprom $&lt; $@

${BIN}.elf: ${OBJS}
    ${CC} ${LDFLAGS} -o $@ $? 
    ${OBJDUMP} -S $@ &gt; ${BIN}.dis

install: ${BIN}.hex
    avrdude -C ./avrdude.conf -c usbasp -p ${MCU} -U flash:w:${BIN}.hex
 -qq

clean:
    rm -f *.o *.elf *.hex

fuses:
    avrdude  -c usbasp -p ${MCU} -C avrdude.conf -U lfuse:w:0xff:m -U h
fuse:w:0xd6:m -U efuse:w:0x05:m -qq