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articles/assembly.md

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+# Assembly
+Assembly, also known as assembler, is family of low-level [programming languages](programming_language.md) that are closely tied to a certain specific
+[CPU](cpu.md) architecture machine code, thus by definition assembly is not portable.
+Assembly is also OS-specific, since it depends on [syscalls](syscall.md) to do anything useful and things like the program
+entrypoint differ between operating systems.
+
+## Examples (x86-64 assembly, Linux)
+```nasm
+default rel                 ; tell the assembler to use RIP-relative addressing
+                            ; instead of absolute memory addresses
+section .text               ; start of the section containing the program's code (.text)
+global _start               ; make entrypoint symbol global
+
+_start:                     ; On Linux, the executable entrypoint symbol name is `_start`
+	mov rax, 0x1            ; sys_write
+	mov rdi, 0x1            ; stdout
+	mov rdx, hello_str_len  ; length of buffer
+	lea rsi, [hello_str]    ; address of buffer
+	syscall
+
+	mov rax, 0x3c           ; sys_exit (60)
+	xor rdi, rdi            ; return code, zero
+	syscall
+
+section .rodata                     ; start of the section containing readonly data (.rodata)
+hello_str: db "Hello world!", 0xa   ; `db` is an assembler directive for embdedding data (a string here)
+hello_str_len: equ $-hello_str      ; assemble-time length calculation
+```
+
+Assembling and linking:
+```sh
+nasm -felf64 -o hello.o hello.asm             # assemble, generates an object file
+cc -static-pie -nostdlib -o hello hello.asm   # now link to get an executable
+```
+
+TODO examples for other architectures