// rt/alloc.s — page allocator via the mmap syscall.
//
// rt_alloc(n: u64) returns a *void aligned at a page boundary, sized
// to the next page multiple. Pair with rt_free(p, n).
//
// We pin to PROT_READ|PROT_WRITE and MAP_PRIVATE|MAP_ANONYMOUS so
// callers never have to plumb file descriptors through.
//
// On mmap failure the raw syscall returns -errno (negative). Task #30
// graduated the `alloc` builtin to a fallible `(*T | nomem)` /
// `([]T | nomem)` signature whose cgen branches on a null return, so
// the failure path here returns 0 instead of a poisoned pointer. The
// builtin's caller is expected to `!`/`?` the result.

TEXT rt_alloc,$0
	MOVQ	DI, SI		// arg 1: length = caller's n
	MOVQ	$0, DI		// arg 0: addr = NULL (kernel chooses)
	MOVQ	$3, DX		// arg 2: prot = R|W
	MOVQ	$34, R10	// arg 3: flags = MAP_PRIVATE|MAP_ANON
	MOVQ	$-1, R8		// arg 4: fd = -1
	MOVQ	$0, R9		// arg 5: offset = 0
	MOVQ	$9, AX		// syscall: mmap
	SYSCALL
	CMPQ	$0, AX
	JGE	rt_alloc_ok
	XORQ	AX, AX
rt_alloc_ok:
	RET

TEXT rt_free,$0
	// DI already holds ptr, SI already holds length
	MOVQ	$11, AX		// syscall: munmap
	SYSCALL
	RET