Fix fork() regression on Windows

Recent optimizations to fork() introduced a regression, that could cause
the subprocess to fail unexpectedly, when TlsAlloc() returns a different
index. This is because we were burning the indexes into the displacement
of x86 opcodes. So when fork() happened and the executable memory copied
it would use the old index. Right now the way this is being solved is to
not copy the executable on fork() and then re-apply code changes. If you
need to be able to preserve self-modified code on fork, reach out and we
can implement a better solution for you. This gets us unblocked quickly.

libc/calls/winexec.c

@@ -80,7 +80,8 @@ textwindows int IsWindowsExecutable(int64_t handle, const char16_t *path) {
   uint32_t got;
   BLOCK_SIGNALS;
   struct NtOverlapped overlap = {.hEvent = CreateEvent(0, 0, 0, 0)};
-  ok = (ReadFile(handle, buf, 2, 0, &overlap) ||
+  ok = overlap.hEvent &&
+       (ReadFile(handle, buf, 2, 0, &overlap) ||
         GetLastError() == kNtErrorIoPending) &&
        GetOverlappedResult(handle, &overlap, &got, true);
   CloseHandle(overlap.hEvent);

libc/proc/describefds.c

@@ -22,7 +22,6 @@
 #include "libc/fmt/itoa.h"
 #include "libc/intrin/fds.h"
 #include "libc/intrin/maps.h"
-#include "libc/intrin/strace.h"
 #include "libc/mem/mem.h"
 #include "libc/nt/files.h"
 #include "libc/nt/runtime.h"
@@ -68,7 +67,6 @@ textwindows void __undescribe_fds(int64_t hCreatorProcess,
                                   uint32_t dwExplicitHandleCount) {
   if (lpExplicitHandles) {
     for (uint32_t i = 0; i < dwExplicitHandleCount; ++i) {
-      STRACE("close handle %lx %lx", hCreatorProcess, lpExplicitHandles[i]);
       DuplicateHandle(hCreatorProcess, lpExplicitHandles[i], 0, 0, 0, false,
                       kNtDuplicateCloseSource);
     }
@@ -127,7 +125,6 @@ textwindows char *__describe_fds(const struct Fd *fds, size_t fdslen,
     for (uint32_t i = 0; i < 3; ++i)
       if (lpStartupInfo->stdiofds[i] == f->handle)
         lpStartupInfo->stdiofds[i] = handle;
-    STRACE("added handle %lx", handle);
     handles[hi++] = handle;
 
     // get shared memory handle for the file offset pointer
@@ -144,7 +141,6 @@ textwindows char *__describe_fds(const struct Fd *fds, size_t fdslen,
         __winerr();
         goto OnFailure;
       }
-      STRACE("added handle %lx", shand);
       handles[hi++] = shand;
     }
 

libc/proc/execve-nt.greg.c

@@ -70,11 +70,8 @@ textwindows int sys_execve_nt(const char *program, char *const argv[],
 
   // execve() needs to be @asyncsignalsafe
   sigset_t sigmask = __sig_block();
-  STRACE("execve step #1");
   _pthread_mutex_lock(&__sig_worker_lock);  // order matters
-  STRACE("execve step #2");
   _pthread_lock();                          // order matters
-  STRACE("execve step #3");
 
   // new process should be a child of our parent
   int64_t hParentProcess =
@@ -83,8 +80,6 @@ textwindows int sys_execve_nt(const char *program, char *const argv[],
                         sys_getppid_nt_win32)
           : 0;
 
-  STRACE("execve step #4");
-
   // inherit pid
   char pidvar[11 + 21];
   FormatUint64(stpcpy(pidvar, "_COSMO_PID="), __pid);
@@ -103,8 +98,6 @@ textwindows int sys_execve_nt(const char *program, char *const argv[],
     setenv("_COSMO_PPID", ppidvar, true);
   }
 
-  STRACE("execve step #5");
-
   // define stdio handles for the spawned subprocess
   struct NtStartupInfo si = {
       .cb = sizeof(struct NtStartupInfo),
@@ -118,8 +111,6 @@ textwindows int sys_execve_nt(const char *program, char *const argv[],
     }
   }
 
-  STRACE("execve step #6");
-
   // which process is responsible for spawning the child?
   int64_t hCreatorProcess;
   if (hParentProcess) {
@@ -140,25 +131,19 @@ textwindows int sys_execve_nt(const char *program, char *const argv[],
     return -1;
   }
 
-  STRACE("execve step #7");
-
   // inherit pending signals
   atomic_fetch_or_explicit(
       __sig.process,
       atomic_load_explicit(&__get_tls()->tib_sigpending, memory_order_acquire),
       memory_order_release);
 
-  STRACE("execve step #8");
-
   // launch the process
   struct NtProcessInformation pi;
   int rc = ntspawn(&(struct NtSpawnArgs){
       AT_FDCWD, program, argv, envp,
       (char *[]){fdspec, maskvar, pidvar, ppidvar, 0}, 0, 0, hCreatorProcess,
       lpExplicitHandles, dwExplicitHandleCount, &si, &pi});
-  STRACE("execve step #9");
   __undescribe_fds(hCreatorProcess, lpExplicitHandles, dwExplicitHandleCount);
-  STRACE("execve step #10");
   if (rc == -1) {
     free(fdspec);
     if (hParentProcess)
@@ -177,11 +162,9 @@ textwindows int sys_execve_nt(const char *program, char *const argv[],
     int64_t handle;
     if (DuplicateHandle(GetCurrentProcess(), pi.hProcess, hParentProcess,
                         &handle, 0, false, kNtDuplicateSameAccess)) {
-      STRACE("execve step #11");
       unassert(!(handle & 0xFFFFFFFFFF000000));
       __imp_TerminateProcess(-1, 0x23000000u | handle);
     } else {
-      STRACE("execve step #12");
       // TODO(jart): Why does `make loc` print this?
       // kprintf("DuplicateHandle failed w/ %d\n", GetLastError());
       __imp_TerminateProcess(-1, ECHILD);

libc/proc/fork-nt.c

@@ -90,6 +90,7 @@ textwindows static void sys_fork_nt_child(void) {
   // setup runtime
   __klog_handle = 0;
   __tls_index = __imp_TlsAlloc();
+  __morph_tls();
   __set_tls_win32(__winmain_tib);
   __tls_enabled = true;
 
@@ -241,6 +242,9 @@ textwindows static int sys_fork_nt_parent(uint32_t dwCreationFlags) {
       }
       if ((map->flags & MAP_NOFORK) && (map->flags & MAP_TYPE) == MAP_FILE) {
         // portable executable segment
+        if (map->prot & PROT_EXEC)
+          // TODO(jart): write a __remorph_tls() function
+          continue;
         if (!(map->prot & PROT_WRITE)) {
           uint32_t child_old_protect;
           ok = ok && !!VirtualProtectEx(procinfo.hProcess, map->addr, allocsize,

libc/proc/fork.c

@@ -298,6 +298,11 @@ int _fork(uint32_t dwCreationFlags) {
       }
     }
 
+    // reactivate ftrace
+    /* if (ftrace_stackdigs) */
+    /*   if (_weaken(ftrace_install)) */
+    /*     _weaken(ftrace_install)(); */
+
     STRACE("fork() → 0 (child of %d)", ppid_cosmo);
   } else {
     // this is the parent process

libc/proc/wait4-nt.c

@@ -131,14 +131,18 @@ textwindows static int __proc_wait(int pid, int *wstatus, int options,
     // perform blocking operation
     uint32_t wi;
     uintptr_t event;
+    if ((event = CreateEvent(0, 0, 0, 0))) {
       struct PosixThread *pt = _pthread_self();
+      pt->pt_event = event;
       pt->pt_blkmask = waitmask;
-    pt->pt_event = event = CreateEvent(0, 0, 0, 0);
       atomic_store_explicit(&pt->pt_blocker, PT_BLOCKER_EVENT,
                             memory_order_release);
       wi = WaitForMultipleObjects(2, (intptr_t[2]){hWaitObject, event}, 0, -1u);
       atomic_store_explicit(&pt->pt_blocker, 0, memory_order_release);
       CloseHandle(event);
+    } else {
+      wi = -1u;
+    }
 
     // log warning if handle unexpectedly closed
     if (wi & kNtWaitAbandoned) {

libc/sock/sendfile.c

@@ -92,9 +92,10 @@ textwindows dontinline static ssize_t sys_sendfile_nt(
   }
   struct NtOverlapped ov = {.hEvent = WSACreateEvent(), .Pointer = offset};
   cosmo_once(&g_transmitfile.once, transmitfile_init);
-  if (g_transmitfile.lpTransmitFile(oh, ih, uptobytes, 0, &ov, 0, 0) ||
+  if (ov.hEvent &&
+      (g_transmitfile.lpTransmitFile(oh, ih, uptobytes, 0, &ov, 0, 0) ||
        WSAGetLastError() == kNtErrorIoPending ||
-      WSAGetLastError() == WSAEINPROGRESS) {
+       WSAGetLastError() == WSAEINPROGRESS)) {
     if (WSAGetOverlappedResult(oh, &ov, &uptobytes, true, &flags)) {
       rc = uptobytes;
       if (opt_in_out_inoffset) {

test/libc/proc/BUILD.mk

@@ -31,6 +31,7 @@ TEST_LIBC_PROC_DIRECTDEPS =						\
 	LIBC_NT_KERNEL32						\
 	LIBC_PROC							\
 	LIBC_RUNTIME							\
+	LIBC_LOG							\
 	LIBC_STDIO							\
 	LIBC_STR							\
 	LIBC_SYSV							\
@@ -90,6 +91,7 @@ o/$(MODE)/test/libc/proc/execve_test.dbg:				\
 		o/$(MODE)/test/libc/proc/execve_test.o			\
 		o/$(MODE)/test/libc/calls/life-nomod.zip.o		\
 		o/$(MODE)/test/libc/proc/execve_test_prog1.zip.o	\
+		o/$(MODE)/test/libc/proc/execve_test_prog2.zip.o	\
 		o/$(MODE)/test/libc/mem/prog/life.elf.zip.o		\
 		o/$(MODE)/test/libc/mem/prog/sock.elf.zip.o		\
 		o/$(MODE)/test/libc/proc/proc.pkg			\
@@ -119,6 +121,7 @@ o/$(MODE)/test/libc/proc/life.dbg:					\
 
 o/$(MODE)/test/libc/proc/life.zip.o					\
 o/$(MODE)/test/libc/proc/execve_test_prog1.zip.o			\
+o/$(MODE)/test/libc/proc/execve_test_prog2.zip.o			\
 o/$(MODE)/test/libc/proc/life-pe.zip.o: private				\
 		ZIPOBJ_FLAGS +=						\
 			-B

test/libc/proc/execve_test.c

@@ -53,6 +53,7 @@ TEST(execve, testArgPassing) {
   char ibuf[12], buf[8];
   const char *prog = "./execve_test_prog1";
   testlib_extract("/zip/execve_test_prog1", prog, 0755);
+  testlib_extract("/zip/execve_test_prog2", "execve_test_prog2", 0755);
   for (i = 0; i < N; ++i) {
     FormatInt32(ibuf, i);
     GenBuf(buf, i);

test/libc/proc/execve_test_prog1.c

@@ -18,6 +18,7 @@
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/calls/calls.h"
 #include "libc/fmt/conv.h"
+#include "libc/runtime/runtime.h"
 #include "libc/str/str.h"
 
 void GenBuf(char buf[8], int x) {
@@ -40,5 +41,15 @@ int main(int argc, char *argv[]) {
     tinyprint(2, "error: buf check failed\n", NULL);
     return 10;
   }
+  const char *prog = "./execve_test_prog2";
+  if (!fork()) {
+    execl(prog, prog, NULL);
+    _Exit(127);
+  }
+  int ws;
+  if (wait(&ws) == -1)
+    return 30;
+  if (ws)
+    return 31;
   return 0;
 }

test/libc/proc/execve_test_prog2.c

@@ -0,0 +1,23 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│ vi: set et ft=c ts=2 sts=2 sw=2 fenc=utf-8                               :vi │
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2024 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/proc/proc.h"
+#include "libc/testlib/testlib.h"
+
+int main(int argc, char *argv[]) {
+}