So I was reading this example on the Wiki Books about x86 Assembly/Interfacing with Linux which has the following code.
.data
msg: .ascii "Hello World\n"
.text
.global _start
_start:
movl $4, %eax # use the `write` [interrupt-flavor] system call
movl $1, %ebx # write to stdout
movl $msg, %ecx # use string "Hello World"
movl $12, %edx # write 12 characters
int $0x80 # make system call
movl $1, %eax # use the `_exit` [interrupt-flavor] system call
movl $0, %ebx # error code 0
int $0x80 # make system call
What I want to know is where can I find documentation or information about what each register does when calling a specific system call.
For example how do I know that movl $1, %ebx writes to stdout or that movl $12, %edx sets the number of characters to write to the buffer.
