clone

pub fn clone() callconv(.naked) u64

File

Code

pub fn clone() callconv(.naked) u64 {
    // __clone(func, stack, flags, arg, ptid, tls, ctid)
    //         3,    4,     5,     6,   7,    8,   9
    //
    // syscall(SYS_clone, flags, stack, ptid, tls, ctid)
    //         0          3,     4,     5,    6,   7
    asm volatile (
        \\  # create initial stack frame for new thread
        \\  clrrdi 4, 4, 4
        \\  li     0, 0
        \\  stdu   0,-32(4)
        \\
        \\  # save fn and arg to child stack
        \\  std    3,  8(4)
        \\  std    6, 16(4)
        \\
        \\  # shuffle args into correct registers and call SYS_clone
        \\  mr    3, 5
        \\  #mr   4, 4
        \\  mr    5, 7
        \\  mr    6, 8
        \\  mr    7, 9
        \\  li    0, 120  # SYS_clone = 120
        \\  sc
        \\
        \\  # if error, negate return (errno)
        \\  bns+  1f
        \\  neg   3, 3
        \\
        \\1:
        \\  # if we're the parent, return
        \\  cmpwi cr7, 3, 0
        \\  bnelr cr7
        \\
        \\  # we're the child
    );
    if (builtin.unwind_tables != .none or !builtin.strip_debug_info) asm volatile (
        \\  .cfi_undefined lr
    );
    asm volatile (
        \\  li    31, 0
        \\  mtlr   0
        \\
        \\  # call fn(arg)
        \\  ld     3, 16(1)
        \\  ld    12,  8(1)
        \\  mtctr 12
        \\  bctrl
        \\
        \\  # call SYS_exit. exit code is already in r3 from fn return value
        \\  li    0, 1    # SYS_exit = 1
        \\  sc
    );
}