More GCC link time issues: undefined reference to main
- by vikramtheone
Hi Guys,
I'm writing software for a Cortex-A8 processor and I have to write some ARM assembly code to access specific registers. I'm making use of the gnu compilers and related tool chains, these tools are installed on the processor board(Freescale i.MX515) with Ubuntu. I make a connection to it from my host PC(Windows) using WinSCP and the PuTTY terminal.
As usual I started with a simple C project having main.c and functions.s. I compile the main.c using GCC, assemble the functions.s using as and link the generated object files using once again GCC, but I get strange errors during this process.
An important finding -
Meanwhile, I found out that my assembly code may have some issues because when I individually assemble it using the command as -o functions.o functions.s and try running the generated functions.o using ./functions.o command, the bash shell is failing to recognize this file as an executable(on pressing tab functions.o is not getting selected/PuTTY is not highlighting the file).
Can anyone suggest whats happening here? Are there any specific options I have to send, to GCC during the linking process? The errors I see are strange and beyond my understanding, I don't understand to what the GCC is referring.
I'm pasting here the contents of main.c, functions.s, the Makefile and the list of errors.
Help, please!!!
Vikram
main.c
#include <stdio.h>
#include <stdlib.h>
int main(void) {
puts("!!!Hello World!!!"); /* prints !!!Hello World!!! */
return EXIT_SUCCESS;
}
functions.s
* Main program */
.equ STACK_TOP, 0x20000800
.text
.global _start
.syntax unified
_start:
.word STACK_TOP, start
.type start, function
start:
movs r0, #10
movs r1, #0
.end
Makefile
all: hello
hello: main.o functions.o
gcc -o main.o functions.o
main.o: main.c
gcc -c -mcpu=cortex-a8 main.c
functions.o: functions.s
as -mcpu=cortex-a8 -o functions.o functions.s
Errors
ubuntu@ubuntu-desktop:~/Documents/Project/Others/helloworld$ make
gcc -c -mcpu=cortex-a8 main.c
as -mcpu=cortex-a8 -o functions.o functions.s
gcc -o main.o functions.o
functions.o: In function `_start':
(.text+0x0): multiple definition of `_start'
/usr/lib/gcc/arm-linux-gnueabi/4.3.3/../../../crt1.o:init.c:(.text+0x0): first defined here
/usr/lib/gcc/arm-linux-gnueabi/4.3.3/../../../crt1.o: In function `_start':
init.c:(.text+0x30): undefined reference to `main'
collect2: ld returned 1 exit status
make: *** [hello] Error 1
