~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~ ~~ System calls for the Linux kernel ~~
~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~
~   The kernel preserves every register except rax, rcx, and r11. The system
~ call number goes in rax, as does the return value. Parameters go in rdi,
~ rsi, rdx, r10, r8, and r9, in that order. [SysV] A.2.1.
~
~   Notice that rsi is our control stack, so we have to save it (for
~ syscalls with at least two parameters). We can use the value stack to do
~ that, since rsp is preserved, or we can use one of the other registers. We
~ don't ourselves save other registers because our caller should do that, if
~ it cares.
~
~   In the kernel source, you may find the following files useful to
~ reference:
~
~   * arch/x86/entry/syscalls/syscall_64.tbl
~   * include/linux/syscalls.h
~   * include/linux/compat.h
~
~   Don't be confused by tools/scripts/syscall.tbl, it's not for x86.
~
~   This file loads early, before dynamic.e. So, although it superficially
~ appears to be able to do allocation and high-level flow control, those come
~ from the transforms, which means they're shallow implementations. The stuff
~ here can't be moved later, because input.e relies on it, and the dynamic
~ stuff relies on that. So, there's additional Linux functionality in another
~ file that loads later, linux-dynamic.e.


~ (call number -- return value)
: syscall-0
  [ here @
    :rax pop-reg64               ~ syscall number
    syscall
    :rax push-reg64              ~ return value
    here ! ] ;asm

~ (first param, call number -- return value)
: syscall-1
  [ here @
    :rax pop-reg64               ~ syscall number
    :rdi pop-reg64               ~ first param
    syscall
    :rax push-reg64              ~ return value
    here ! ] ;asm

~ (first param, second param, call number -- return value)
: syscall-2
  [ here @
    :rsi :rbx mov-reg64-reg64    ~ save rsi
    :rax pop-reg64               ~ syscall number
    :rsi pop-reg64               ~ second param
    :rdi pop-reg64               ~ first param
    syscall
    :rbx :rsi mov-reg64-reg64    ~ restore rsi
    :rax push-reg64              ~ return value
    here ! ] ;asm

~ (first param, second param, third param, call number -- return value)
: syscall-3
  [ here @
    :rsi :rbx mov-reg64-reg64    ~ save rsi
    :rax pop-reg64               ~ syscall number
    :rdx pop-reg64               ~ third param
    :rsi pop-reg64               ~ second param
    :rdi pop-reg64               ~ first param
    syscall
    :rbx :rsi mov-reg64-reg64    ~ restore rsi
    :rax push-reg64              ~ return value
    here ! ] ;asm

~ (first param, second param, third param, fourth param, call number
~  -- return value)
: syscall-4
  [ here @
    :rsi :rbx mov-reg64-reg64    ~ save rsi
    :rax pop-reg64               ~ syscall number
    :r10 pop-extrareg64          ~ fourth param
    :rdx pop-reg64               ~ third param
    :rsi pop-reg64               ~ second param
    :rdi pop-reg64               ~ first param
    syscall
    :rbx :rsi mov-reg64-reg64    ~ restore rsi
    :rax push-reg64              ~ return value
    here ! ] ;asm


~ (first param, second param, third param, fourth param, fifth param,
~  call number -- return value)
: syscall-5
  [ here @
    :rsi :rbx mov-reg64-reg64    ~ save rsi
    :rax pop-reg64               ~ syscall number
    :r8 pop-extrareg64           ~ fifth param
    :r10 pop-extrareg64          ~ fourth param
    :rdx pop-reg64               ~ third param
    :rsi pop-reg64               ~ second param
    :rdi pop-reg64               ~ first param
    syscall
    :rbx :rsi mov-reg64-reg64    ~ restore rsi
    :rax push-reg64              ~ return value
    here ! ] ;asm


~ (first param, second param, third param, fourth param, fifth param,
~  sixth param, call number -- return value)
: syscall-6
  [ here @
    :rsi :rbx mov-reg64-reg64    ~ save rsi
    :rax pop-reg64               ~ syscall number
    :r9 pop-extrareg64           ~ sixth param
    :r8 pop-extrareg64           ~ fifth param
    :r10 pop-extrareg64          ~ fourth param
    :rdx pop-reg64               ~ third param
    :rsi pop-reg64               ~ second param
    :rdi pop-reg64               ~ first param
    syscall
    :rbx :rsi mov-reg64-reg64    ~ restore rsi
    :rax push-reg64              ~ return value
    here ! ] ;asm


~ Raw system calls
~ ~~~~~~~~~~~~~~~~

~   This does the Linux exit() system call, passing it an exit code taken
~ from the stack. It does not return.
~
~ (exit code -- *)
: sys-exit 60 syscall-1
  ~ In the event we're still here, let's minimize confusion.
  crash ;

~   This does the Linux write() system call, passing it an address from the
~ top of the stack and a length from the second position on the stack. It
~ uses a Unix file descriptor, which is a non-negative integer, to tell it
~ where to write to. For stdout, use fd 1.
~
~ (file descriptor, base address, length to write -- result code or length)
: sys-write 1 syscall-3 ;

~ (file descriptor, base address, length to read -- result code or length)
: sys-read 0 syscall-3 ;

~ (filename, flags, mode -- result code or file descriptor)
: sys-open 2 syscall-3 ;

~ (file descriptor -- result code)
: sys-close 3 syscall-1 ;