Initial commit

.gitignore

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+*.o
+*.bin

Makefile

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+NASM=/usr/local/bin/nasm
+LD=ld
+
+all: hello_world.bin hello_world64.bin
+
+hello_world.o:
+	$(NASM) -f macho hello_world.asm
+hello_world.bin: hello_world.o
+	$(LD) -e main -macosx_version_min 10.7.0 -lSystem  -o hello_world.bin hello_world.o
+
+hello_world64.o:
+	$(NASM) -f macho64 hello_world64.asm
+hello_world64.bin: hello_world64.o
+	$(LD) -e main -macosx_version_min 10.7.0 -lSystem -o hello_world64.bin hello_world64.o
+
+clean:
+	rm -f *.o
+	rm -f *.bin

README.md

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+# Hello World in NASM assembly for OS X (32 & 64 bit)
+
+I won't promise this is done "the right way" (tm), I've never really
+used assembly but wanted to play around with it some.
+Everything seems to work under OS X Lion.
+
+To assemble the 64 bit version you'll need to build your own nasm (use
+homebrew).
+
+## Thanks
+These, among other sources, where helpful:
+* http://thexploit.com/secdev/mac-os-x-64-bit-assembly-system-calls/
+* http://www.x86-64.org/documentation/abi.pdf
+* http://michaux.ca/articles/assembly-hello-world-for-os-x

hello_world.asm

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+    SECTION .data
+msg:    db    "Hello World!", 0x0a
+len:    equ   $-msg
+
+    SECTION .text
+    global main
+
+kernel:
+    int 0x80
+    ret
+
+main:
+    mov eax, 4         ; SYS_write
+    push dword len
+    push dword msg
+    push dword 1       ; stdout
+    call kernel
+    add esp, 12
+    
+    push dword 0
+    mov eax, 1
+    call kernel

hello_world64.asm

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+    SECTION .data
+msg:    db    "Hello World!", 0x0a
+len:    equ   $-msg
+
+    SECTION .text
+    global main
+
+kernel:
+    syscall
+    ret
+
+main:
+    mov rax, 0x2000004   ; SYS_write
+    mov rdi, 1
+    mov rsi, msg
+    mov rdx, len
+    call kernel
+    
+    mov rax, 0x2000001
+    mov rdi, 0
+    call kernel