syscall6

pub fn syscall6(
    number: SYS,
    arg1: syscall_arg_t,
    arg2: syscall_arg_t,
    arg3: syscall_arg_t,
    arg4: syscall_arg_t,
    arg5: syscall_arg_t,
    arg6: syscall_arg_t,
) u32

File

Code

pub fn syscall6(
    number: SYS,
    arg1: syscall_arg_t,
    arg2: syscall_arg_t,
    arg3: syscall_arg_t,
    arg4: syscall_arg_t,
    arg5: syscall_arg_t,
    arg6: syscall_arg_t,
) u32 {
    // arg6 can't be passed to asm in a register because ebp might be reserved as the frame pointer
    // and there are no more GPRs available; so we'll need a memory operand for it. Adding that
    // memory operand means that on PIC we might need a reference to the GOT, which in turn needs
    // *its* own GPR, so we need to pass another arg in memory too! This is surprisingly hard to get
    // right, because we can't touch esp or ebp until we're done with the memory input (as that
    // input could be relative to esp or ebp).
    const args56: [2]syscall_arg_t = .{ arg5, arg6 };
    return asm volatile (
        \\ push %[args56]
        \\ push %%ebp
        \\ mov 4(%%esp), %%ebp
        \\ mov %%edi, 4(%%esp)
        \\ // The saved %%edi and %%ebp are on the stack, and %%ebp points to `args56`.
        \\ // Prepare the last two args, syscall, then pop the saved %%ebp and %%edi.
        \\ mov (%%ebp), %%edi
        \\ mov 4(%%ebp), %%ebp
        \\ int  $0x80
        \\ pop  %%ebp
        \\ pop  %%edi
        : [ret] "={eax}" (-> u32),
        : [number] "{eax}" (@backingInt(number)),
          [arg1] "{ebx}" (arg1),
          [arg2] "{ecx}" (arg2),
          [arg3] "{edx}" (arg3),
          [arg4] "{esi}" (arg4),
          [args56] "rm" (&args56),
        : .{ .memory = true });
}