[llvm] [clang] [clang-tools-extra] [flang] [flang] Add EXECUTE_COMMAND_LINE runtime and lowering intrinsics implementation (PR #74077)

[Yi Wu via cfe-commits]

================
@@ -0,0 +1,206 @@
+//===-- runtime/execute.cpp -----------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "flang/Runtime/execute.h"
+#include "environment.h"
+#include "stat.h"
+#include "terminator.h"
+#include "tools.h"
+#include "flang/Runtime/descriptor.h"
+#include <cstdlib>
+#include <future>
+#include <limits>
+#ifdef _WIN32
+#define LEAN_AND_MEAN
+#define NOMINMAX
+#include <windows.h>
+#else
+#include <signal.h>
+#include <unistd.h>
+#endif
+
+namespace Fortran::runtime {
+
+// cmdstat specified in 16.9.73
+// −1 if the processor does not support command line execution,
+// a processor-dependent positive value if an error condition occurs
+// −2 if no error condition occurs but WAIT is present with the value false
+// and the processor does not support asynchronous execution. Otherwise it is
+// assigned the value 0
+enum CMD_STAT {
+  ASYNC_NO_SUPPORT_ERR = -2,
+  NO_SUPPORT_ERR = -1,
+  CMD_EXECUTED = 0,
+  FORK_ERR = 1,
+  EXECL_ERR = 2,
+  INVALID_CL_ERR = 3,
+  SIGNAL_ERR = 4
+};
+
+// Override CopyCharsToDescriptor in tools.h, pass string directly
+void CopyCharsToDescriptor(const Descriptor &value, const char *rawValue) {
+  CopyCharsToDescriptor(value, rawValue, std::strlen(rawValue));
+}
+
+void CheckAndCopyCharsToDescriptor(
+    const Descriptor *value, const char *rawValue) {
+  if (value) {
+    CopyCharsToDescriptor(*value, rawValue);
+  }
+}
+
+void CheckAndStoreIntToDescriptor(
+    const Descriptor *intVal, std::int64_t value, Terminator &terminator) {
+  if (intVal) {
+    StoreIntToDescriptor(intVal, value, terminator);
+  }
+}
+
+// If a condition occurs that would assign a nonzero value to CMDSTAT but
+// the CMDSTAT variable is not present, error termination is initiated.
+int TerminationCheck(int status, const Descriptor *cmdstat,
+    const Descriptor *cmdmsg, Terminator &terminator) {
+  if (status == -1) {
+    if (!cmdstat) {
+      terminator.Crash("Execution error with system status code: %d", status);
+    } else {
+      CheckAndStoreIntToDescriptor(cmdstat, EXECL_ERR, terminator);
+      CopyCharsToDescriptor(*cmdmsg, "Execution error");
+    }
+  }
+#ifdef _WIN32
+  // On WIN32 API std::system returns exit status directly
+  int exitStatusVal{status};
+  if (exitStatusVal == 1) {
+#else
+  int exitStatusVal{WEXITSTATUS(status)};
+  if (exitStatusVal == 127 || exitStatusVal == 126) {
+#endif
+    if (!cmdstat) {
+      terminator.Crash(
+          "Invalid command quit with exit status code: %d", exitStatusVal);
+    } else {
+      CheckAndStoreIntToDescriptor(cmdstat, INVALID_CL_ERR, terminator);
+      CopyCharsToDescriptor(*cmdmsg, "Invalid command line");
+    }
+  }
+#if defined(WIFSIGNALED) && defined(WTERMSIG)
+  if (WIFSIGNALED(status)) {
+    if (!cmdstat) {
+      terminator.Crash("killed by signal: %d", WTERMSIG(status));
+    } else {
+      CheckAndStoreIntToDescriptor(cmdstat, SIGNAL_ERR, terminator);
+      CopyCharsToDescriptor(*cmdmsg, "killed by signal");
+    }
+  }
+#endif
+#if defined(WIFSTOPPED) && defined(WSTOPSIG)
+  if (WIFSTOPPED(status)) {
+    if (!cmdstat) {
+      terminator.Crash("stopped by signal: %d", WSTOPSIG(status));
+    } else {
+      CheckAndStoreIntToDescriptor(cmdstat, SIGNAL_ERR, terminator);
+      CopyCharsToDescriptor(*cmdmsg, "stopped by signal");
+    }
+  }
+#endif
+  return exitStatusVal;
+}
+
+void RTNAME(ExecuteCommandLine)(const Descriptor &command, bool wait,
+    const Descriptor *exitstat, const Descriptor *cmdstat,
+    const Descriptor *cmdmsg, const char *sourceFile, int line) {
+  Terminator terminator{sourceFile, line};
+  const char *newCmd{EnsureNullTerminated(
+      command.OffsetElement(), command.ElementBytes(), terminator)};
+
+  if (exitstat) {
+    RUNTIME_CHECK(terminator, IsValidIntDescriptor(exitstat));
+  }
+
+  if (cmdstat) {
+    RUNTIME_CHECK(terminator, IsValidIntDescriptor(cmdstat));
+    // Assigned 0 as specifed in standard, if error then overwrite
+    StoreIntToDescriptor(cmdstat, CMD_EXECUTED, terminator);
+  }
+
+  if (cmdmsg) {
+    RUNTIME_CHECK(terminator, IsValidCharDescriptor(cmdmsg));
+  }
+
+  if (wait) {
+    // either wait is not specified or wait is true: synchronous mode
+    int status{std::system(newCmd)};
+    int exitStatusVal{TerminationCheck(status, cmdstat, cmdmsg, terminator)};
+    // If sync, assigned processor-dependent exit status. Otherwise unchanged
+    CheckAndStoreIntToDescriptor(exitstat, exitStatusVal, terminator);
+  } else {
+// Asynchronous mode
+#ifdef _WIN32
+    STARTUPINFO si;
+    PROCESS_INFORMATION pi;
+    ZeroMemory(&si, sizeof(si));
+    si.cb = sizeof(si);
+    ZeroMemory(&pi, sizeof(pi));
+
+    // add "cmd.exe /c " to the beginning of command
+    const char *prefix{"cmd.exe /c "};
+    char *newCmdWin{(char *)AllocateMemoryOrCrash(
+        terminator, std::strlen(prefix) + std::strlen(newCmd) + 1)};
+    std::strcpy(newCmdWin, prefix);
+    std::strcat(newCmdWin, newCmd);
+
+    // Convert the char to wide char
+    const size_t sizeNeeded{mbstowcs(NULL, newCmdWin, 0) + 1};
+    wchar_t *wcmd{(wchar_t *)AllocateMemoryOrCrash(
+        terminator, sizeNeeded * sizeof(wchar_t))};
+    if (std::mbstowcs(wcmd, newCmdWin, sizeNeeded) == static_cast<size_t>(-1)) {
+      terminator.Crash("Char to wide char failed for newCmd");
+    }
+    FreeMemory((void *)newCmdWin);
+
+    if (CreateProcess(nullptr, wcmd, nullptr, nullptr, FALSE, 0, nullptr,
+            nullptr, &si, &pi)) {
+      // Close handles so it will be removed when terminated
+      CloseHandle(pi.hProcess);
+      CloseHandle(pi.hThread);
+    } else {
+      if (!cmdstat) {
+        terminator.Crash(
+            "CreateProcess failed with error code: %lu.", GetLastError());
+      } else {
+        StoreIntToDescriptor(cmdstat, (uint32_t)GetLastError(), terminator);
+        CheckAndCopyCharsToDescriptor(cmdmsg, "CreateProcess failed.");
+      }
+    }
+    FreeMemory((void *)wcmd);
+#else
+    // terminated children do not become zombies
+    signal(SIGCHLD, SIG_IGN);
----------------
yi-wu-arm wrote:

It turns out that resetting the signal doesn't work well. put `signal(SIGCHLD, SIG_IGN)` will still cause system return -1. However, using a non-blocking `waitpid` to get the exit code of child process will clear up the zombie. (I didn't there is an non-blocking wait).
```cpp
void sigchld_handler(int signo) {
    int status;
    waitpid(-1, &status, WNOHANG); // WNOHANG means non-blocking
}
.......
signal(SIGCHLD, sigchld_handler);
pid_t pid{fork()};
if (pid < 0) {
  error;
} else if (pid == 0) {
  std::system(cmd);
}
```

https://github.com/llvm/llvm-project/pull/74077