GNU assembly programming directly on an ARM920T running Debian (not cross-compiling)

wmnelis · 12-29-2009, 11:13 AM

I am trying to write some very simple assembly code directly on an Excito Bubba Server (https://www.excito.com/bubba/products/overview.html). The server has an ARM920T processor and runs Debian. I am writing the code directly on the device by ssh-ing into it (as-in I am not cross-compiling). So far I have been unable to get anything to work. I always get a segfault. I am a novice at Assembly programming, I have done some in college and some on my own on an x86 machine with no trouble.

Here is an example of some code I have written:

Code:

.section .text

.global	_start

_start:
	ADD	r0, r0, r1
	MOV	pc, lr

Here is the makefile I am using to assemble and link this code:

Code:

##
## Macros
##

# Environment macros
AS=as
LD=ld
RM=rm -f

# Project macros
EXE_NAME=hello #Put the name you want the executable to have here
ASFLAGS=-mcpu=arm920t --gdwarf2 #gdwarf2 creates a debug info file
LDFLAGS=

##
## File List
##

# Project file list (leave off the suffixes)
SOURCE_FILES=		\
	hello

# 3rd party file list
LIBRARIES=			\
	#Put any required 3rd party libraries here

##
## Suffix rules (do not change)
##

##
## Commands (do not change)
##

# Build the executable only
exe:				\
	compile			\
	all

# Compile all files
compile: ${SOURCE_FILES:=.s}
	${AS} ${ASFLAGS} -o ${SOURCE_FILES:=.o} ${SOURCE_FILES:=.s} ${LIBRARIES}

# Link object files into executable
all: ${SOURCE_FILES:=.o}
	${LD} ${LDFLAGS} -o ${EXE_NAME} ${SOURCE_FILES:=.o} ${LIBRARIES}

# Get rid of all non-source files
clean:
	${RM} ${EXE_NAME} ${SOURCE_FILES:=.o}

This example will create an executable, but it will segfault immediately. Anyone out there know what I am doing wrong?

Thanks for any help you can offer.

wmnelis · 12-29-2009, 02:49 PM

Just to add, the following C code with inline assembly works just fine on the same machine:

Source code:

Code:

#include <stdio.h>

main()
{
  // Declare a variable that will contain a calculated value
  int i = 0;

  // Set the values to add
  int a = 2;
  int b = 4;

  // Add the values and store the result in the "i" C variable
  asm volatile
    ("add %0, %1, %2" // <-- Assembly code
     : "=r"(i)        // <-- Outputs
     : "r"(a), "r"(b) // <-- Inputs
     : "r0", "r1"     // <-- Clobber list
    );

  // Output the calculated value
  printf("The value: %d\n", i);
}

Makefile:

Code:

CC = /usr/bin/gcc


all:
	${CC} -c add.c
	$(CC) -o add add.o

clean:
	rm add *.o