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

[Michael Jones via libc-commits]

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@@ -0,0 +1,141 @@
+//===-- Implementation of setenv ------------------------------------------===//
+//
+// 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 "src/stdlib/setenv.h"
+#include "environ_internal.h"
+#include "src/__support/CPP/string_view.h"
+#include "src/__support/common.h"
+#include "src/__support/libc_errno.h"
+#include "src/__support/macros/config.h"
+#include "src/string/memcpy.h"
+#include "src/string/strlen.h"
+
+// We use extern "C" declarations for malloc/free instead of including
+// src/stdlib/malloc.h and src/stdlib/free.h. This allows the implementation
+// to work with different allocator implementations, particularly in integration
+// tests which provide a simple bump allocator. The extern "C" linkage ensures
+// we use whatever allocator is linked with the test or application.
+extern "C" void *malloc(size_t);
+extern "C" void free(void *);
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(int, setenv,
+                   (const char *name, const char *value, int overwrite)) {
+  // Validate inputs
+  if (name == nullptr || value == nullptr) {
+    libc_errno = EINVAL;
+    return -1;
+  }
+
+  cpp::string_view name_view(name);
+  if (name_view.empty()) {
+    libc_errno = EINVAL;
+    return -1;
+  }
+
+  // POSIX: name cannot contain '='
+  if (name_view.find_first_of('=') != cpp::string_view::npos) {
+    libc_errno = EINVAL;
+    return -1;
+  }
+
+  // Lock mutex for thread safety
+  internal::environ_mutex.lock();
+
+  // Initialize environ if not already done
+  internal::init_environ();
+
+  // Search for existing variable
+  int index = internal::find_env_var(name_view);
+
+  if (index >= 0) {
+    // Variable exists
+    if (overwrite == 0) {
+      // Don't overwrite, just return success
+      internal::environ_mutex.unlock();
+      return 0;
+    }
+
+    // Need to replace the value
+    // Calculate size for "name=value" string
+    size_t name_len = LIBC_NAMESPACE::strlen(name);
+    size_t value_len = LIBC_NAMESPACE::strlen(value);
+    size_t total_len =
+        name_len + 1 + value_len + 1; // name + '=' + value + '\0'
+
+    char *new_string = reinterpret_cast<char *>(malloc(total_len));
+    if (!new_string) {
+      internal::environ_mutex.unlock();
+      libc_errno = ENOMEM;
+      return -1;
+    }
+
+    // Build "name=value" string
+    LIBC_NAMESPACE::memcpy(new_string, name, name_len);
----------------
michaelrj-google wrote:

generally we want to avoid calling the public names of libc functions. The recommended pattern here is to use `inline_memcpy` and `#include "src/string/memory_utils/inline_memcpy.h"`

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