Make fixes and improvements

- Document more compiler flags
- Expose new __print_maps() api
- Better overflow checking in mmap()
- Improve the shell example somewhat
- Fix minor runtime bugs regarding stacks
- Make kill() on fork()+execve()'d children work
- Support CLONE_CHILD_CLEARTID for proper joining
- Fix recent possible deadlock regression with --ftrace

libc/runtime/winthreadlaunch.S

@@ -0,0 +1,46 @@
+/*-*- mode:unix-assembly; indent-tabs-mode:t; tab-width:8; coding:utf-8     -*-│
+│vi: set et ft=asm ts=8 tw=8 fenc=utf-8                                     :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2022 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ Permission to use, copy, modify, and/or distribute this software for         │
+│ any purpose with or without fee is hereby granted, provided that the         │
+│ above copyright notice and this permission notice appear in all copies.      │
+│                                                                              │
+│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
+│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
+│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
+│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
+│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
+│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
+│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
+│ PERFORMANCE OF THIS SOFTWARE.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/macros.internal.h"
+.text.windows
+
+//	Used by clone() on Windows to launch thread.
+//
+//	Windows owns the stack memory when we initially enter threads.
+//	This function switches us over, so that we can start using the
+//	runtime facilities.
+//
+//	@param	%rdi is arg
+//	@param	%rsi is func
+//	@param	%rdx is stack
+//	@return	%rax is exit code
+//	@see	clone()
+WinThreadLaunch:
+	push	%rbx
+	push	%r15
+	mov	%rbp,%r15
+	mov	%rsp,%rbx
+	mov	%rdx,%rsp
+	xor	%rbp,%rbp
+	call	*%rsi
+	mov	%r15,%rbp
+	mov	%rbx,%rsp
+	pop	%r15
+	pop	%rbx
+	ret
+	.endfn	WinThreadLaunch,globl,hidden