Add initial openbsd skeleton

1 files changed, 65 insertions, 0 deletions

diff --git a/rt/start-openbsd.s b/rt/start-openbsd.s
new file mode 100644
index 0000000..54cd0ce
--- /dev/null
+++ b/rt/start-openbsd.s
@@ -0,0 +1,65 @@
+.data
+/* std._environment : byte[:][:] */
+.globl sys$__environment
+sys$__environment:
+.envbase:
+.quad 0 /* env size */
+.envlen:
+.quad 0 /* env ptr */
+
+.globl sys$__cenvp
+sys$__cenvp:
+.quad 0
+
+.text
+/*
+ * The entry point for the whole program.
+ * This is called by the OS. In order, it:
+ *  - Sets up all argc entries as slices
+ *  - Sets up all envp entries as slices
+ *  - Converts argc/argv to a slice
+ *  - Stashes envp in std._environment
+ *  - Stashes a raw envp copy in __cenvp (for syscalls to use)
+ *  - Calls main()
+ */
+.globl _start
+_start:
+	/* stack allocate sizeof(byte[:])*(argc + len(envp)) */
+	movq	(%rdi),%rax
+	leaq	16(%rdi,%rax,8), %rbx	/* argp = argv + 8*argc + 8 */
+	call    count
+	addq	%r9,%rax
+	imulq	$16,%rax
+	subq	%rax,%rsp
+	movq	%rsp, %rdx	/* saved args[:] */
+
+	/* convert envp to byte[:][:] for std._environment */
+	movq	(%rdi),%rax
+	leaq	16(%rdi,%rax,8), %rbx	/* envp = argv + 8*argc + 8 */
+	/* store envp for some syscalls to use without spurious conversion. */
+	movq    %rbx,sys$__cenvp(%rip)
+	movq	%r9,%rax
+	movq	%rsp, %rcx
+	movq	%r9,.envlen(%rip)
+	movq	%rdx,.envbase(%rip)
+	call	cvt
+	movq	%rcx,%rdx
+
+	/* convert argc, argv to byte[:][:] for args. */
+	movq	(%rdi), %rax	/* argc */
+	leaq	8(%rdi), %rbx	/* argv */
+	movq	(%rdi), %rsi	/* saved argc */
+	call    cvt
+	pushq   %rsi
+	pushq   %rdx
+
+	/* call pre-main initializers */
+	call	__init__
+
+	/* enter the main program */
+	call	main
+	/* exit(0) */
+	xorq	%rdi,%rdi
+	movq	$1,%rax
+	syscall
+