CMSC313, Computer Organization & Assembly Language Programming, Fall 2012
NASM Help
Setting Up
On linux.gl.umbc.edu, first find out if your shell variables are
configured correctly. Type:
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which -a nasm
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You should see /usr/bin/nasm. If not, need to add
/usr/bin/ to your PATH environment variable.
Currently, OIT has two versions of nasm installed on the GL
system. The one we want is in /usr/bin. You can use
the alias command to make sure that you use the correct version:
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alias nasm /usr/bin/nasm
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If you are using Bourne shell, use the syntax:
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alias nasm=/usr/bin/nasm
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Use the ps command to identify your shell. If you see
bash or sh, you are using Bourne shell. If you
see tcsh or csh, you are using C shell.
After issuing the alias command, try invoking nasm
with the -version switch. You should see something like:
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linux2% nasm -version
NASM version 2.07 compiled on Feb 25 2010
linux2%
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You can place the alias command in your .cshrc or
.tcshrc (which ever one you use). That way you
don't have to issue the alias command every time you log in.
If you have a 32-bit Linux installation, you can run
nasm on your own machine. Other flavors of Unix are not
compatible, including 64-bit Linux, BSD Unix, MacOS X. You can run
nasm on these machines and produce 32-bit ELF object code, but
you cannot run it. Check that you have a recent installation of
nasm:
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nasm -version
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The latest version is available from
the official NASM web site.
(The latest version as of August 2012 is 2.10.04.)
Running NASM
Suppose you have an assembly language program in a file called
"hello.asm". You can assemble it for Linux with the command:
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nasm -f elf hello.asm
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The "-f elf" option tells nasm to output the object code in the Executable
and Linking Format (ELF) that Linux uses. This creates an object file
called "hello.o". The object code is still not executable. To create
an executable file, we must use the linking loader "ld":
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ld hello.o
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This then creates an "a.out" file that you can execute from the Linux
command line.
If the loader complains that it cannot find the entry symbol _start, it is
because you do not have a global label _start for the entry point of your
program. To fix this problem, the beginning of the code section of your
program should look like:
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SECTION .text ; Code section.
global _start
_start: ; Entry point.
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Another useful option in nasm is "-l" for specifying a listing file. The
command:
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nasm -f elf hello.asm -l hello.lst
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which will produce a listing file named "hello.lst". The listing file
conatins both the source listing of the assembly language program and the
machine code for each assembly language operation.
The "-g" option tells nasm to generate debugging information
for use in gdb:
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nasm -f elf -g hello.asm -l hello.lst
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For more information on running NASM, consult
Chapter 2 of the online NASM manual, or type
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nasm -help
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Last Modified:
19 Sep 2012 22:03:01 EDT
by
Richard Chang
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