[libc-commits] [libc] [libc] Implement execvp in unistd (PR #232427)

[Pavel Labath via libc-commits]

================
@@ -0,0 +1,162 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// Linux implementation of execvp.
+///
+//===----------------------------------------------------------------------===//
+
+#include "src/unistd/execvp.h"
+
+#include "hdr/errno_macros.h"
+#include "hdr/types/size_t.h"
+#include "src/__support/CPP/string_view.h"
+#include "src/__support/CPP/stringstream.h"
+#include "src/__support/OSUtil/linux/syscall_wrappers/execve.h"
+#include "src/__support/common.h"
+#include "src/__support/libc_errno.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/macros/null_check.h"
+#include "src/unistd/environ.h"
+
+#include <linux/limits.h>
+
+namespace LIBC_NAMESPACE_DECL {
+
+namespace {
+
+LIBC_INLINE const char *get_path() {
+  if (LIBC_NAMESPACE::environ == nullptr)
+    return nullptr;
+
+  for (char **env = LIBC_NAMESPACE::environ; *env != nullptr; ++env) {
+    cpp::string_view entry(*env);
+    if (entry.starts_with("PATH="))
+      return *env + 5;
+  }
+  return nullptr;
+}
+
+LIBC_INLINE int execve_with_fallback(const char *path, char *const argv[],
+                                     char *const envp[]) {
+  auto ret = linux_syscalls::execve(path, argv, envp);
+  if (!ret && ret.error() == ENOEXEC) {
+    size_t argc = 0;
+    while (argv[argc] != nullptr)
+      ++argc;
+
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wvla"
+#if __has_warning("-Wvla-cxx-extension")
+#pragma GCC diagnostic ignored "-Wvla-cxx-extension"
+#endif
+    char *new_argv[argc + 2];
+#pragma GCC diagnostic pop
+    new_argv[0] = const_cast<char *>("sh");
+    new_argv[1] = const_cast<char *>(path);
+    for (size_t i = 1; i <= argc; ++i)
+      new_argv[i + 1] = argv[i];
+
+    ret = linux_syscalls::execve("/bin/sh", new_argv, envp);
+  }
+  if (!ret) {
+    libc_errno = ret.error();
+    return -1;
+  }
+  return *ret;
+}
+
+} // namespace
+
+LLVM_LIBC_FUNCTION(int, execvp, (const char *file, char *const argv[])) {
+  LIBC_CRASH_ON_NULLPTR(file);
+
+  if (file[0] == '\0') {
+    libc_errno = ENOENT;
+    return -1;
+  }
+
+  char *const *envp = const_cast<char *const *>(LIBC_NAMESPACE::environ);
+
+  cpp::string_view file_view(file);
+  if (file_view.contains('/'))
+    return execve_with_fallback(file, argv, envp);
+
+  const char *path = get_path();
+  // POSIX standard default path if PATH is not set.
+  if (path == nullptr)
+    path = ":/bin:/usr/bin";
----------------
labath wrote:

Are you sure about that? I'd be surprised if "." was on the default path -- and in the first place, no less

```suggestion
    path = "/bin:/usr/bin";
```

https://github.com/llvm/llvm-project/pull/232427