GNU Assembler - Example Programs

Example Programs

A standard “Hello, world!” program for Linux on IA-32:

.data msg: .asciz "Hello, world!\n" # "asciz" will cause the assembler to append # the null byte that many C library routines # expect. The C library isn't being used in # the example. MSGLEN = . - msg # this will cause the assembler to count the number of bytes # between the label "msg" and here. The number will be 16, # as the null byte is included. .text .globl _start _start: movl $MSGLEN,%edx # argument 3 for write. Number of bytes to write. # A macro is used, which means the MSGLEN will be # replaced with the immediate value 0xf (15) during # assembly. Comparable to C preprocessor macros. movl $msg,%ecx # argument 2 for write. Pointer to data. movl $1,%ebx # argument 1. file descriptor number. (stdout=1, see article on file descriptors) movl $4,%eax # syscall number 4 = write(2) int $0x80 xorl %ebx,%ebx # argument for syscall. exit code = 0 (xor of a value with itself always equals 0) movl $1,%eax # syscall number 1 = exit(2) int $0x80

A standard “Hello, world!” program for FreeBSD and Mac OS X on IA-32:

.data msg: .asciz "Hello, world!\n" MSGLEN = . - msg .text .globl _start _start: pushl $MSGLEN pushl $msg pushl $1 movl $4,%eax subl $4,%esp int $0x80 addl $16 pushl $0 movl $1,%eax subl $4,%esp int $0x80