Get fork() working on Windows

This is done without using Microsoft's internal APIs. MAP_PRIVATE
mappings are copied to the subprocess via a pipe, since Microsoft
doesn't want us to have proper COW pages. MAP_SHARED mappings are
remapped without needing to do any copying. Global variables need
copying along with the stack and the whole heap of anonymous mem.
This actually improves the reliability of the redbean http server
although one shouldn't expect 10k+ connections on a home computer
that isn't running software built to serve like Linux or FreeBSD.

libc/calls/commandv.c

@@ -24,6 +24,7 @@
 #include "libc/dce.h"
 #include "libc/errno.h"
 #include "libc/nt/ntdll.h"
+#include "libc/runtime/missioncritical.h"
 #include "libc/runtime/runtime.h"
 #include "libc/str/str.h"
 #include "libc/sysv/consts/ok.h"
@@ -32,7 +33,7 @@
 static int accessexe(char pathname[hasatleast PATH_MAX], size_t len,
                      const char *ext) {
   len = stpcpy(&pathname[len], ext) - &pathname[0];
-  if (access(pathname, X_OK) != -1) {
+  if (isexecutable(pathname)) {
     return len;
   } else {
     return -1;
@@ -48,7 +49,7 @@ static int accesscmd(char pathname[hasatleast PATH_MAX], const char *path,
   pathlen = strlen(path);
   if (pathlen + 1 + namelen + 1 + 4 + 1 > PATH_MAX) return -1;
   p = mempcpy(pathname, path, pathlen);
-  if (pathlen) *p++ = '/';
+  if (pathlen && pathname[pathlen - 1] != '/') *p++ = '/';
   p = mempcpy(p, name, namelen);
   len = p - &pathname[0];
   hasdot = !!memchr(basename(name), '.', namelen);

libc/calls/dup-nt.c

@@ -44,7 +44,7 @@ textwindows int dup$nt(int oldfd, int newfd, int flags) {
   }
   if (DuplicateHandle(GetCurrentProcess(), g_fds.p[oldfd].handle,
                       GetCurrentProcess(), &g_fds.p[newfd].handle, 0,
-                      (flags & O_CLOEXEC), kNtDuplicateSameAccess)) {
+                      flags & O_CLOEXEC, kNtDuplicateSameAccess)) {
     g_fds.p[newfd].kind = g_fds.p[oldfd].kind;
     g_fds.p[newfd].flags = flags;
     return newfd;

libc/calls/hefty/dirstream.c

@@ -134,7 +134,7 @@ DIR *opendir(const char *name) {
   DIR *res;
   if (!IsWindows() && !IsXnu()) {
     res = NULL;
-    if ((fd = open(name, O_RDONLY | O_DIRECTORY | O_CLOEXEC, 0)) != -1) {
+    if ((fd = open(name, O_RDONLY | O_DIRECTORY | O_CLOEXEC)) != -1) {
       if (!(res = fdopendir(fd))) close(fd);
     }
     return res;

libc/calls/hefty/fork-nt.c

@@ -0,0 +1,158 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2020 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ This program is free software; you can redistribute it and/or modify         │
+│ it under the terms of the GNU General Public License as published by         │
+│ the Free Software Foundation; version 2 of the License.                      │
+│                                                                              │
+│ This program is distributed in the hope that it will be useful, but          │
+│ WITHOUT ANY WARRANTY; without even the implied warranty of                   │
+│ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU             │
+│ General Public License for more details.                                     │
+│                                                                              │
+│ You should have received a copy of the GNU General Public License            │
+│ along with this program; if not, write to the Free Software                  │
+│ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA                │
+│ 02110-1301 USA                                                               │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/calls/calls.h"
+#include "libc/calls/hefty/spawn.h"
+#include "libc/calls/internal.h"
+#include "libc/conv/itoa.h"
+#include "libc/nt/enum/filemapflags.h"
+#include "libc/nt/enum/pageflags.h"
+#include "libc/nt/ipc.h"
+#include "libc/nt/memory.h"
+#include "libc/nt/process.h"
+#include "libc/nt/runtime.h"
+#include "libc/runtime/memtrack.h"
+#include "libc/runtime/missioncritical.h"
+#include "libc/runtime/runtime.h"
+#include "libc/sysv/consts/map.h"
+#include "libc/sysv/consts/prot.h"
+#include "libc/sysv/errfuns.h"
+
+static textwindows int64_t ParseInt(char16_t **p) {
+  uint64_t x = 0;
+  while ('0' <= **p && **p <= '9') {
+    x *= 10;
+    x += *(*p)++ - '0';
+  }
+  return x;
+}
+
+static textwindows void WriteAll(int64_t h, void *buf, size_t n) {
+  char *p;
+  size_t i;
+  uint32_t wrote;
+  for (p = buf, i = 0; i < n; i += wrote) {
+    WriteFile(h, p + i, n - i, &wrote, NULL);
+  }
+}
+
+static textwindows void ReadAll(int64_t h, void *buf, size_t n) {
+  char *p;
+  size_t i;
+  uint32_t got;
+  for (p = buf, i = 0; i < n; i += got) {
+    ReadFile(h, p + i, n - i, &got, NULL);
+  }
+}
+
+textwindows void WinMainForked(void) {
+  int64_t h;
+  void *addr;
+  jmp_buf jb;
+  char16_t *p;
+  uint64_t size;
+  char16_t var[21 + 1 + 21 + 1];
+  uint32_t i, varlen, protect, access;
+  varlen = GetEnvironmentVariable(u"_FORK", var, ARRAYLEN(var));
+  if (!varlen || varlen >= ARRAYLEN(var)) return;
+  p = var;
+  h = ParseInt(&p);
+  if (*p++ == ' ') CloseHandle(ParseInt(&p));
+  ReadAll(h, jb, sizeof(jb));
+  ReadAll(h, &_mmi.i, sizeof(_mmi.i));
+  for (i = 0; i < _mmi.i; ++i) {
+    ReadAll(h, &_mmi.p[i], sizeof(_mmi.p[i]));
+    addr = (void *)((uint64_t)_mmi.p[i].x << 16);
+    size = ((uint64_t)(_mmi.p[i].y - _mmi.p[i].x) << 16) + FRAMESIZE;
+    switch (_mmi.p[i].prot) {
+      case PROT_READ | PROT_WRITE | PROT_EXEC:
+        protect = kNtPageExecuteReadwrite;
+        access = kNtFileMapRead | kNtFileMapWrite | kNtFileMapExecute;
+        break;
+      case PROT_READ | PROT_WRITE:
+        protect = kNtPageReadwrite;
+        access = kNtFileMapRead | kNtFileMapWrite;
+        break;
+      case PROT_READ:
+        protect = kNtPageReadonly;
+        access = kNtFileMapRead;
+        break;
+      default:
+        protect = kNtPageNoaccess;
+        access = 0;
+        break;
+    }
+    if (_mmi.p[i].flags & MAP_PRIVATE) {
+      MapViewOfFileExNuma(
+          (_mmi.p[i].h = CreateFileMappingNuma(-1, NULL, protect, 0, size, NULL,
+                                               kNtNumaNoPreferredNode)),
+          access, 0, 0, size, addr, kNtNumaNoPreferredNode);
+      ReadAll(h, addr, size);
+    } else {
+      MapViewOfFileExNuma(_mmi.p[i].h, access, 0, 0, size, addr,
+                          kNtNumaNoPreferredNode);
+    }
+  }
+  ReadAll(h, _edata, _end - _edata);
+  CloseHandle(h);
+  longjmp(jb, 1);
+}
+
+textwindows int fork$nt(void) {
+  jmp_buf jb;
+  int64_t reader, writer;
+  int i, rc, pid, fds[3];
+  char *p, buf[21 + 1 + 21 + 1];
+  if (!setjmp(jb)) {
+    if (CreatePipe(&reader, &writer, &kNtIsInheritable, 0)) {
+      p = buf;
+      p += uint64toarray_radix10(reader, p);
+      *p++ = ' ';
+      p += uint64toarray_radix10(writer, p);
+      setenv("_FORK", buf, true);
+      fds[0] = 0;
+      fds[1] = 1;
+      fds[2] = 2;
+      /* TODO: CloseHandle(g_fds.p[pid].h) if SIGCHLD is SIG_IGN */
+      if ((pid = spawnve(0, fds, g_argv[0], g_argv, environ)) != -1) {
+        CloseHandle(reader);
+        WriteAll(writer, jb, sizeof(jb));
+        WriteAll(writer, &_mmi.i, sizeof(_mmi.i));
+        for (i = 0; i < _mmi.i; ++i) {
+          WriteAll(writer, &_mmi.p[i], sizeof(_mmi.p[i]));
+          if (_mmi.p[i].flags & MAP_PRIVATE) {
+            WriteAll(writer, (void *)((uint64_t)_mmi.p[i].x << 16),
+                     ((uint64_t)(_mmi.p[i].y - _mmi.p[i].x) << 16) + FRAMESIZE);
+          }
+        }
+        WriteAll(writer, _edata, _end - _edata);
+        CloseHandle(writer);
+        rc = pid;
+      } else {
+        rc = -1;
+      }
+      unsetenv("_FORK");
+    } else {
+      rc = winerr();
+    }
+  } else {
+    rc = 0;
+  }
+  return rc;
+}

libc/calls/hefty/fork.c

@@ -20,6 +20,7 @@
 #include "libc/bits/bits.h"
 #include "libc/calls/calls.h"
 #include "libc/calls/internal.h"
+#include "libc/dce.h"
 
 /**
  * Creates new process zygote style.
@@ -29,7 +30,13 @@
  */
 int fork(void) {
   int rc;
-  rc = fork$sysv();
-  if (rc == 0) __onfork();
+  if (!IsWindows()) {
+    rc = fork$sysv();
+  } else {
+    rc = fork$nt();
+  }
+  if (rc == 0) {
+    __onfork();
+  }
   return rc;
 }

libc/calls/hefty/ntspawn.c

@@ -25,8 +25,10 @@
 #include "libc/calls/hefty/ntspawn.h"
 #include "libc/calls/internal.h"
 #include "libc/conv/conv.h"
+#include "libc/nt/enum/processcreationflags.h"
 #include "libc/nt/process.h"
 #include "libc/nt/runtime.h"
+#include "libc/runtime/missioncritical.h"
 #include "libc/runtime/runtime.h"
 #include "libc/str/str.h"
 #include "libc/sysv/consts/fileno.h"

libc/calls/hefty/spawnlp.c

@@ -21,6 +21,7 @@
 #include "libc/calls/hefty/mkvarargv.h"
 #include "libc/calls/hefty/spawn.h"
 #include "libc/mem/mem.h"
+#include "libc/runtime/missioncritical.h"
 #include "libc/runtime/runtime.h"
 
 /**

libc/calls/hefty/spawnve-nt.c

@@ -67,7 +67,7 @@ textwindows int spawnve$nt(unsigned flags, int stdiofds[3], const char *program,
   }
 
   if (handle != -1 &&
-      ntspawn(program, argv, envp, NULL, NULL,
+      ntspawn(program, argv, envp, &kNtIsInheritable, NULL,
               (flags & SPAWN_TABULARASA) ? false : true,
               (flags & SPAWN_DETACH)
                   ? (kNtCreateNewProcessGroup | kNtDetachedProcess |
@@ -83,7 +83,7 @@ textwindows int spawnve$nt(unsigned flags, int stdiofds[3], const char *program,
       if (handle != -1) {
         stdiofds[i] = tubes[i];
         g_fds.p[tubes[i]].kind = kFdFile;
-        g_fds.p[tubes[i]].flags = O_CLOEXEC;
+        g_fds.p[tubes[i]].flags = 0;
         CloseHandle(sti.stdiofds[i]);
       } else {
         CloseHandle(tubes[i]);

libc/calls/hefty/vfork.S

@@ -0,0 +1,50 @@
+/*-*- 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 2020 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ This program is free software; you can redistribute it and/or modify         │
+│ it under the terms of the GNU General Public License as published by         │
+│ the Free Software Foundation; version 2 of the License.                      │
+│                                                                              │
+│ This program is distributed in the hope that it will be useful, but          │
+│ WITHOUT ANY WARRANTY; without even the implied warranty of                   │
+│ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU             │
+│ General Public License for more details.                                     │
+│                                                                              │
+│ You should have received a copy of the GNU General Public License            │
+│ along with this program; if not, write to the Free Software                  │
+│ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA                │
+│ 02110-1301 USA                                                               │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/dce.h"
+#include "libc/macros.h"
+
+/	Forks process without copying page tables.
+/
+/	This is the same as fork() except it's optimized for the case
+/	where the caller invokes exec() immediately afterwards.
+/
+/	@return	pid of child process or 0 if forked process
+/	@returnstwice
+vfork:	testb	IsWindows()
+	jnz	fork$nt
+	mov	__NR_vfork(%rip),%eax
+	cmp	$-1,%eax
+	je	systemfive.enosys
+	pop	%rsi
+	testb	IsBsd()
+	jnz	vfork.bsd
+	syscall
+	push	%rsi
+	cmp	$-4095,%rax
+	jae	systemfive.error
+	ret
+	.endfn	vfork,globl
+
+vfork.bsd:
+	syscall
+	push	%rsi
+	jc	systemfive.errno
+	ret
+	.endfn	vfork.bsd

libc/calls/internal.h

@@ -56,11 +56,11 @@ struct Fds {
 
 extern const struct Fd kEmptyFd;
 
-extern int g_sighandrvas[NSIG] hidden;
-extern struct Fds g_fds hidden;
-extern struct NtSystemInfo g_ntsysteminfo hidden;
-extern struct NtStartupInfo g_ntstartupinfo hidden;
-extern const struct NtSecurityAttributes kNtIsInheritable hidden;
+hidden extern int g_sighandrvas[NSIG];
+hidden extern struct Fds g_fds;
+hidden extern struct NtSystemInfo g_ntsysteminfo;
+hidden extern struct NtStartupInfo g_ntstartupinfo;
+hidden extern const struct NtSecurityAttributes kNtIsInheritable;
 
 ssize_t createfd(void) hidden;
 int growfds(void) hidden;
@@ -218,6 +218,7 @@ void xnutrampoline(void *, i32, i32, const struct __darwin_siginfo *,
 int gettimeofday$nt(struct timeval *, struct timezone *) hidden;
 bool32 isatty$nt(int) hidden;
 char *getcwd$nt(char *, size_t) hidden;
+int fork$nt(void) hidden;
 int chdir$nt(const char *) hidden;
 int close$nt(int) hidden;
 int dup$nt(int, int, int) hidden;
@@ -258,6 +259,7 @@ int nanosleep$nt(const struct timespec *, struct timespec *) hidden;
 │ cosmopolitan § syscalls » windows nt » support                           ─╬─│┼
 ╚────────────────────────────────────────────────────────────────────────────│*/
 
+void WinMainForked(void) hidden;
 int getsetpriority$nt(int, unsigned, int, int (*)(int));
 void ntcontext2linux(struct ucontext *, const struct NtContext *) hidden;
 struct NtOverlapped *offset2overlap(int64_t, struct NtOverlapped *) hidden;

libc/calls/wait.c

@@ -18,9 +18,6 @@
 │ 02110-1301 USA                                                               │
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/calls/calls.h"
-#include "libc/calls/internal.h"
-#include "libc/dce.h"
-#include "libc/sysv/errfuns.h"
 
 /**
  * Waits for status to change on any child process.
@@ -31,9 +28,5 @@
  * @asyncsignalsafe
  */
 int wait(int *opt_out_wstatus) {
-  if (!IsWindows()) {
-    return wait4$sysv(-1, opt_out_wstatus, 0, NULL);
-  } else {
-    return enosys(); /* TODO(jart) */
-  }
+  return wait4(-1, opt_out_wstatus, 0, NULL);
 }

libc/calls/wait4-nt.c

@@ -21,11 +21,14 @@
 #include "libc/calls/internal.h"
 #include "libc/calls/struct/rusage.h"
 #include "libc/conv/conv.h"
+#include "libc/macros.h"
 #include "libc/nt/accounting.h"
 #include "libc/nt/enum/status.h"
+#include "libc/nt/enum/wait.h"
 #include "libc/nt/runtime.h"
 #include "libc/nt/struct/filetime.h"
 #include "libc/nt/synchronization.h"
+#include "libc/runtime/missioncritical.h"
 #include "libc/runtime/runtime.h"
 #include "libc/str/str.h"
 #include "libc/sysv/consts/w.h"
@@ -33,34 +36,51 @@
 
 textwindows int wait4$nt(int pid, int *opt_out_wstatus, int options,
                          struct rusage *opt_out_rusage) {
+  int pids[64];
+  int64_t handles[64];
   uint32_t dwExitCode;
+  uint32_t i, count, timeout;
   struct NtFileTime createfiletime, exitfiletime, kernelfiletime, userfiletime;
-  if (!isfdkind(pid, kFdProcess)) return esrch();
-  for (;;) {
-    dwExitCode = kNtStillActive;
-    if (!(options & WNOHANG)) {
-      WaitForSingleObject(g_fds.p[pid].handle, 0xffffffff);
+  if (pid != -1) {
+    if (!isfdkind(pid, kFdProcess)) {
+      return echild();
     }
-    if (GetExitCodeProcess(g_fds.p[pid].handle, &dwExitCode)) {
-      if (dwExitCode != kNtStillActive) {
-        if (opt_out_wstatus) { /* @see WEXITSTATUS() */
-          *opt_out_wstatus = (dwExitCode & 0xff) << 8;
-        }
-        if (opt_out_rusage) {
-          memset(opt_out_rusage, 0, sizeof(*opt_out_rusage));
-          GetProcessTimes(GetCurrentProcess(), &createfiletime, &exitfiletime,
-                          &kernelfiletime, &userfiletime);
-          FileTimeToTimeVal(&opt_out_rusage->ru_utime, userfiletime);
-          FileTimeToTimeVal(&opt_out_rusage->ru_stime, kernelfiletime);
-        }
-        return pid;
-      } else if (options & WNOHANG) {
-        return pid;
-      } else {
-        continue;
+    handles[0] = g_fds.p[pid].handle;
+    pids[0] = pid;
+    count = 1;
+  } else {
+    for (count = 0, i = g_fds.n; i--;) {
+      if (g_fds.p[i].kind == kFdProcess) {
+        pids[count] = i;
+        handles[count] = g_fds.p[i].handle;
+        if (++count == ARRAYLEN(handles)) break;
       }
-    } else {
-      return winerr();
+    }
+    if (!count) {
+      return echild();
     }
   }
+  for (;;) {
+    dwExitCode = kNtStillActive;
+    if (options & WNOHANG) {
+      i = WaitForMultipleObjects(count, handles, false, 0);
+      if (i == kNtWaitTimeout) return 0;
+    } else {
+      i = WaitForMultipleObjects(count, handles, false, -1);
+    }
+    if (i == kNtWaitFailed) return winerr();
+    if (!GetExitCodeProcess(handles[i], &dwExitCode)) return winerr();
+    if (dwExitCode == kNtStillActive) continue;
+    if (opt_out_wstatus) { /* @see WEXITSTATUS() */
+      *opt_out_wstatus = (dwExitCode & 0xff) << 8;
+    }
+    if (opt_out_rusage) {
+      memset(opt_out_rusage, 0, sizeof(*opt_out_rusage));
+      GetProcessTimes(GetCurrentProcess(), &createfiletime, &exitfiletime,
+                      &kernelfiletime, &userfiletime);
+      FileTimeToTimeVal(&opt_out_rusage->ru_utime, userfiletime);
+      FileTimeToTimeVal(&opt_out_rusage->ru_stime, kernelfiletime);
+    }
+    return pids[i];
+  }
 }

libc/calls/zygote.c

@@ -17,8 +17,11 @@
 │ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA                │
 │ 02110-1301 USA                                                               │
 ╚─────────────────────────────────────────────────────────────────────────────*/
-#include "libc/nt/struct/securityattributes.h"
 #include "libc/calls/internal.h"
+#include "libc/nt/struct/securityattributes.h"
 
 const struct NtSecurityAttributes kNtIsInheritable = {
-    sizeof(struct NtSecurityAttributes), NULL, true};
+    sizeof(struct NtSecurityAttributes),
+    NULL,
+    true,
+};