[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) {
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michaelrj-google wrote:

the two sides of this `if` are very similar. They both allocate space for `needed`, then update the internal variables. It would be cleaner to combine the parts where the branches are the same.

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