Appendix F: Linux System Call Tables

This appendix provides system call numbers and argument conventions for the three architectures covered in this book. All values are for the Linux kernel.

Argument conventions: - x86-64: syscall instruction; number in RAX; args in RDI, RSI, RDX, R10, R8, R9; return in RAX - ARM64: svc #0 instruction; number in X8; args in X0, X1, X2, X3, X4, X5; return in X0 - RISC-V: ecall instruction; number in a7; args in a0, a1, a2, a3, a4, a5; return in a0

Note: ARM64 and RISC-V Linux use the same syscall numbers (from the generic syscall table in include/uapi/asm-generic/unistd.h). x86-64 uses a separate historical table.

File I/O

Memory Management

mmap Protection Flags (prot argument)

mmap Map Flags (flags argument)

Process and Thread Management

Signals

Common Signal Numbers

Networking

Time

Clock IDs

Error Return Conventions

On success, most syscalls return 0 (or a positive value such as a file descriptor or byte count).

On error, syscalls return a negative value equal to the negated errno constant. For example: - -2 = ENOENT (No such file or directory) - -12 = ENOMEM (Out of memory) - -22 = EINVAL (Invalid argument) - -9 = EBADF (Bad file descriptor) - -11 = EAGAIN / EWOULDBLOCK (Resource temporarily unavailable)

The C library wrapper functions (read(), write(), etc.) detect negative return values, negate them, store the result in errno, and return -1 to the calling C code.

In assembly, after syscall, check if rax is in the range -4095 to -1 to detect an error. The kernel guarantees that successful return values are not in this range (with the exception of mmap, which can return addresses near 0xFFFFFFFFFFFFF000).

Quick Assembly Templates

Hello World (x86-64)

section .data
    msg db "Hello, World!", 10
    msglen equ $ - msg

section .text
    global _start
_start:
    mov rax, 1          ; write
    mov rdi, 1          ; stdout
    lea rsi, [rel msg]  ; buffer
    mov rdx, msglen     ; length
    syscall

    mov rax, 60         ; exit
    xor rdi, rdi        ; status 0
    syscall

Hello World (ARM64)

.data
msg: .ascii "Hello, World!\n"
msglen = . - msg

.text
.global _start
_start:
    mov x8, #64         // write
    mov x0, #1          // stdout
    adr x1, msg         // buffer
    mov x2, #msglen     // length
    svc #0

    mov x8, #93         // exit
    mov x0, #0          // status 0
    svc #0

Hello World (RISC-V)

.data
msg: .ascii "Hello, World!\n"
msglen = . - msg

.text
.global _start
_start:
    li a7, 64           # write
    li a0, 1            # stdout
    la a1, msg          # buffer
    li a2, msglen       # length
    ecall

    li a7, 93           # exit
    li a0, 0            # status 0
    ecall