Function syscall2_readonly 

pub unsafe fn syscall2_readonly(
    sysno: Sysno,
    arg0: usize,
    arg1: usize,
) -> Result<usize, Errno>

Available on (Linux or Android) and (x86-64 and little-endian and 64-bit, or AArch64 and 64-bit, or ARM and 32-bit, or x86 and little-endian and 32-bit), or Linux and (x86-64 and little-endian and 32-bit, or RISC-V RV64 and little-endian and 64-bit, or RISC-V RV32 and little-endian and 32-bit, or MIPS and 32-bit, or MIPS-64 and 64-bit, or s390x and big-endian and 64-bit, or LoongArch LA64 and little-endian and 64-bit, or PowerPC and big-endian and 32-bit, or PowerPC-64 and 64-bit) only.

Make a raw system call with 2 arguments. Like the non _readonly version but you declare that syscall does not mutate any memory.

Returns a Result<usize, Errno>.

Safety

A system call is unsafe by definition. It’s the caller’s responsibility to ensure safety.