[libc-commits] [libc] [libc][stdlib] Implement setenv() with environment management infrastructure (PR #163018)

[Michael Jones via libc-commits]

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@@ -0,0 +1,144 @@
+//===-- Implementation of internal environment utilities ------------------===//
+//
+// 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 "environ_internal.h"
+#include "config/app.h"
+#include "hdr/func/free.h"
+#include "hdr/func/malloc.h"
+#include "hdr/func/realloc.h"
+#include "src/__support/CPP/string_view.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+namespace internal {
+
+// Minimum initial capacity for the environment array when first allocated.
+// This avoids frequent reallocations for small environments.
+constexpr size_t MIN_ENVIRON_CAPACITY = 32;
+
+// Growth factor for environment array capacity when expanding.
+// When capacity is exceeded, new_capacity = old_capacity *
+// ENVIRON_GROWTH_FACTOR.
+constexpr size_t ENVIRON_GROWTH_FACTOR = 2;
+
+char **EnvironmentManager::get_array() {
+  if (is_ours)
+    return storage;
+  return reinterpret_cast<char **>(LIBC_NAMESPACE::app.env_ptr);
+}
+
+void EnvironmentManager::init() {
+  // Count entries in the startup environ
+  char **env_ptr = reinterpret_cast<char **>(LIBC_NAMESPACE::app.env_ptr);
+  if (!env_ptr)
+    return;
+
+  size_t count = 0;
+  for (char **env = env_ptr; *env != nullptr; env++)
+    count++;
+
+  size = count;
+}
+
+int EnvironmentManager::find_var(cpp::string_view name) {
+  char **env_array = get_array();
+  if (!env_array)
+    return -1;
+
+  for (size_t i = 0; i < size; i++) {
+    cpp::string_view current(env_array[i]);
+    if (!current.starts_with(name))
+      continue;
+
+    // Check that name is followed by '='
+    if (current.size() > name.size() && current[name.size()] == '=')
+      return static_cast<int>(i);
+  }
+
+  return -1;
+}
+
+bool EnvironmentManager::ensure_capacity(size_t needed) {
+  // If we're still using the startup environ, we need to copy it
+  if (!is_ours) {
+    char **old_env = reinterpret_cast<char **>(LIBC_NAMESPACE::app.env_ptr);
+
+    // Allocate new array with room to grow
+    size_t new_capacity = needed < MIN_ENVIRON_CAPACITY
+                              ? MIN_ENVIRON_CAPACITY
+                              : needed * ENVIRON_GROWTH_FACTOR;
+    char **new_storage =
+        reinterpret_cast<char **>(malloc(sizeof(char *) * (new_capacity + 1)));
+    if (!new_storage)
+      return false;
+
+    // Allocate ownership tracking array
+    EnvStringOwnership *new_ownership = reinterpret_cast<EnvStringOwnership *>(
+        malloc(sizeof(EnvStringOwnership) * (new_capacity + 1)));
+    if (!new_ownership) {
+      free(new_storage);
+      return false;
+    }
+
+    // Copy existing pointers (we don't own the strings yet, so just copy
+    // pointers)
+    if (old_env) {
+      for (size_t i = 0; i < size; i++) {
+        new_storage[i] = old_env[i];
+        // Initialize ownership: startup strings are not owned by us
+        new_ownership[i] = EnvStringOwnership();
+      }
+    }
+    new_storage[size] = nullptr;
+
+    storage = new_storage;
+    ownership = new_ownership;
+    capacity = new_capacity;
+    is_ours = true;
+
+    // Update app.env_ptr to point to our storage
+    LIBC_NAMESPACE::app.env_ptr = reinterpret_cast<uintptr_t *>(storage);
----------------
michaelrj-google wrote:

this is already inside of `LIBC_NAMESPACE`, so specifying the namespace may not be necessary.

https://github.com/llvm/llvm-project/pull/163018