clone

pub fn clone() callconv(.naked) u64

File

Code

pub fn clone() callconv(.naked) u64 {
    asm volatile (
        \\# int clone(
        \\#    fn,      a = r2
        \\#    stack,   b = r3
        \\#    flags,   c = r4
        \\#    arg,     d = r5
        \\#    ptid,    e = r6
        \\#    tls,     f = *(r15+160)
        \\#    ctid)    g = *(r15+168)
        \\#
        \\# pseudo C code:
        \\# tid = syscall(SYS_clone,b,c,e,g,f);
        \\# if (!tid) syscall(SYS_exit, a(d));
        \\# return tid;
        \\
        \\# preserve call-saved register used as syscall arg
        \\stg  %%r6, 48(%%r15)
        \\
        \\# create initial stack frame for new thread
        \\nill %%r3, 0xfff8
        \\aghi %%r3, -160
        \\lghi %%r0, 0
        \\stg  %%r0, 0(%%r3)
        \\
        \\# save fn and arg to child stack
        \\stg  %%r2,  8(%%r3)
        \\stg  %%r5, 16(%%r3)
        \\
        \\# shuffle args into correct registers and call SYS_clone
        \\lgr  %%r2, %%r3
        \\lgr  %%r3, %%r4
        \\lgr  %%r4, %%r6
        \\lg   %%r5, 168(%%r15)
        \\lg   %%r6, 160(%%r15)
        \\svc  120
        \\
        \\# restore call-saved register
        \\lg   %%r6, 48(%%r15)
        \\
        \\# if error or if we're the parent, return
        \\ltgr %%r2, %%r2
        \\bnzr %%r14
        \\
        \\# we're the child
    );
    if (builtin.unwind_tables != .none or !builtin.strip_debug_info) asm volatile (
        \\.cfi_undefined %%r14
    );
    asm volatile (
        \\lghi %%r11, 0
        \\lghi %%r14, 0
        \\
        \\# call fn(arg)
        \\lg   %%r1,  8(%%r15)
        \\lg   %%r2, 16(%%r15)
        \\basr %%r14, %%r1
        \\
        \\# call SYS_exit. exit code is already in r2 from fn return value
        \\svc  1
        \\
    );
}