// rt/start.s — process entry. Linux sets up the stack so that on
// entry [SP] holds argc, [SP+8] starts argv (NULL-terminated array
// of *u8), [SP+8+(argc+1)*8] starts envp (also NULL-terminated).
//
// We pull argc into DI and the argv pointer into SI, then jump to
// `main`. ww programs that declare `fn main(argc: i32, argv: **u8)
// i32` see them; programs declaring `fn main() i32` simply ignore
// the regs. Either way, main's return value is fed to the exit
// syscall.
//
// envp is captured into the rt_envp_slot DATAW cell before CALL main
// so lib/os.getenv (via the rt_envp getter below) can walk it. We
// compute envp = SP + 16 + argc*8 in AX using three doublings and
// adds — w6a's syntax doesn't ship SIB-style indexed addressing
// (no `LEAQ 16(SP)(DI*8), AX`), so the explicit shift-by-three is
// the portable form. AX/DI/SI are scratch on entry; no callee-
// saved discipline applies until we reach main.
TEXT _start,$0
	MOVQ	(SP), DI		// argc → DI (1st arg to main)
	LEAQ	8(SP), SI		// &argv[0] → SI (2nd arg to main)
	MOVQ	DI, AX			// AX = argc
	ADDQ	AX, AX			// AX = argc * 2
	ADDQ	AX, AX			// AX = argc * 4
	ADDQ	AX, AX			// AX = argc * 8
	ADDQ	SP, AX			// AX = SP + argc*8
	ADDQ	$16, AX			// AX = SP + argc*8 + 16 = &argv[argc+1] = envp
	MOVQ	AX, rt_envp_slot(SB)
	// argc/argv survive the envp calc (only AX was clobbered): stash both
	// so lib/os.args can rebuild the []str view after entry. Same DATAW-
	// slot + TEXT-getter shape as rt_envp below (task #17 fnmatch filter).
	MOVQ	DI, rt_argc_slot(SB)
	MOVQ	SI, rt_argv_slot(SB)
	CALL	main(SB)
	MOVQ	AX, DI
	MOVQ	$60, AX
	SYSCALL

// rt_envp — getter that returns the envp pointer captured at process
// entry. Bound from lib/os via `@symbol("rt_envp") fn rtenvp() **u8;`,
// matching the rt_syscall / rt_malloc / rt_abort pattern. Read-only
// view of the kernel-supplied table; the bytes live for the process
// lifetime. A future setenv that grows the table re-points the slot
// (separate task).
TEXT rt_envp,$0
	MOVQ	rt_envp_slot(SB), AX
	RET

// rt_envp_slot — 8-byte writable cell holding the envp pointer.
// Initialised to zero in .data; _start overwrites it before
// transferring control to main. DATAW gives us the writable .data
// slot (w6a has no GLOBL; same shape as lib/log's silent/default/
// global cells in lib/log/log.s).
DATAW	rt_envp_slot(SB),"\x00\x00\x00\x00\x00\x00\x00\x00"

// rt_argc — getter returning the process argc captured at entry. Bound
// from lib/os as `@symbol("rt_argc") fn rtargc() i64;` (rt_envp twin).
TEXT rt_argc,$0
	MOVQ	rt_argc_slot(SB), AX
	RET

// rt_argv — getter returning &argv[0], a NUL-terminated table of *u8
// argument strings. Bound from lib/os as
// `@symbol("rt_argv") fn rtargv() **u8;`.
TEXT rt_argv,$0
	MOVQ	rt_argv_slot(SB), AX
	RET

// rt_argc_slot / rt_argv_slot — 8-byte writable cells, zero in .data,
// overwritten by _start before CALL main. Same shape as rt_envp_slot.
DATAW	rt_argc_slot(SB),"\x00\x00\x00\x00\x00\x00\x00\x00"
DATAW	rt_argv_slot(SB),"\x00\x00\x00\x00\x00\x00\x00\x00"