Included header's function is undefined - linux

Question

I am currently trying to compile some code using linux for the first time. After reading some basic information about makefiles, i have come across an issue that I could not resolve.
Using the Tiva Makefile template:
# Tiva Makefile
# #####################################
#
# Part of the uCtools project
# uctools.github.com
#
#######################################
# user configuration:
#######################################
# TARGET: name of the output file
TARGET = main
# MCU: part number to build for
MCU = TM4C123GH6PM
# SOURCES: list of input source sources
SOURCES = main.c startup_gcc.c
# INCLUDES: list of includes, by default, use Includes directory
INCLUDES = $(HOME)/embedded/zekeTiva/Include
# OUTDIR: directory to use for output
OUTDIR = build
# TIVAWARE_PATH: path to tivaware folder
TIVAWARE_PATH = $(HOME)/embedded/tivaware
# LD_SCRIPT: linker script
LD_SCRIPT = $(MCU).ld
# define flags
CFLAGS = -g -mthumb -mcpu=cortex-m4 -mfpu=fpv4-sp-d16 -mfloat-abi=softfp
CFLAGS +=-Os -ffunction-sections -fdata-sections -MD -std=c99 -Wall
CFLAGS += -pedantic -DPART_$(MCU) -c -I$(TIVAWARE_PATH) -I$(INCLUDES)
CFLAGS += -DTARGET_IS_BLIZZARD_RA1
LDFLAGS = -T $(LD_SCRIPT) --entry ResetISR --gc-sections
#######################################
# end of user configuration
#######################################
#
#######################################
# binaries
#######################################
CC = arm-none-eabi-gcc
LD = arm-none-eabi-ld
OBJCOPY = arm-none-eabi-objcopy
RM = rm -f
MKDIR = mkdir -p
#######################################
# list of object files, placed in the build directory regardless of source path
OBJECTS = $(addprefix $(OUTDIR)/,$(notdir $(SOURCES:.c=.o)))
# default: build bin
all: $(OUTDIR)/$(TARGET).bin
$(OUTDIR)/%.o: src/%.c | $(OUTDIR)
$(CC) -o $# $^ $(CFLAGS)
$(OUTDIR)/a.out: $(OBJECTS)
$(LD) -o $# $^ $(LDFLAGS)
$(OUTDIR)/main.bin: $(OUTDIR)/a.out
$(OBJCOPY) -O binary $< $#
# create the output directory
$(OUTDIR):
$(MKDIR) $(OUTDIR)
clean:
-$(RM) $(OUTDIR)/*
.PHONY: all clean
Using this makefile, I am able to compile and use functions from any of .h files in the TIVAWARE path. However, even though I can include the headers from the INCLUDE path, my functions from included headers are "undefined". Since this is not the main point of the project, I decided to use the Tiva template, but this is really something that is out of my depth.

Answer 1

Showing undefined reference means there is some linking error.
Add your library containing function definitions from TIVAWARE_PATH and INCLUDES path in LDFLAGS and then recompile.