[libc-commits] [libc] [libc] Refactor core Linux syscalls to use syscall_wrappers (PR #185983)

[Alexey Samsonov via libc-commits]

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@@ -0,0 +1,68 @@
+.. _syscall_wrapper_refactor:
+
+==============================
+Syscall Wrapper Refactoring
+==============================
+
+Purpose
+=======
+
+LLVM-libc is transitioning to a centralized system for Linux syscalls. The goal
+is to move all direct ``syscall_impl`` calls into a dedicated directory:
+``src/__support/OSUtil/linux/syscall_wrappers/``.
+
+This refactor provides several benefits:
+
+* **Type Safety**: Using ``ErrorOr<T>`` ensures that error conditions are
+  handled explicitly.
+* **Consistency**: Standardizes the conversion of syscall return values into
+  errno-compatible objects.
+* **Maintainability**: Centralizes platform-specific syscall logic, making it
+  easier to audit and update.
+
+The Pattern
+===========
+
+Each syscall should have its own header-only library in the ``syscall_wrappers``
+directory. The wrapper function should return an ``ErrorOr<T>``.
+
+Example Wrapper (``src/__support/OSUtil/linux/syscall_wrappers/read.h``):
+--------------------------------------------------------------------------
+
+.. code-block:: c++
+
+    #include "src/__support/OSUtil/linux/syscall.h" // For syscall_impl
+    #include "src/__support/error_or.h"
+    #include "src/__support/common.h"
+    #include <sys/syscall.h> // For syscall numbers
+
+    namespace LIBC_NAMESPACE_DECL {
+    namespace internal {
+
+    LIBC_INLINE ErrorOr<ssize_t> read(int fd, void *buf, size_t count) {
+      ssize_t ret = syscall_impl<ssize_t>(SYS_read, fd, buf, count);
+      if (ret < 0) {
+        return Error(-static_cast<int>(ret));
+      }
+      return ret;
+    }
+
+    } // namespace internal
+    } // namespace LIBC_NAMESPACE_DECL
+
+How to Migrate
+==============
+
+1. **Create the Wrapper**: Add a new header file in
+   ``src/__support/OSUtil/linux/syscall_wrappers/``.
+2. **Update CMake**: Add a ``add_header_library`` target for the new wrapper in
+   ``src/__support/OSUtil/linux/syscall_wrappers/CMakeLists.txt``.
+3. **Refactor Entrypoints**:
+
+   * Include the new wrapper header (e.g., ``read.h``).
+   * Replace direct ``syscall_impl`` calls with ``internal::<function_name>``.
+   * Update the entrypoint's ``DEPENDS`` in ``CMakeLists.txt`` to include the
+     new wrapper target.
+
+4. **Cleanup OSUtil**: If the syscall was previously implemented manually in
----------------
vonosmas wrote:

I think we might want to make it a first step - if the syscall was previously implemented, remove the old implementation to replace it with the new wrapper.

https://github.com/llvm/llvm-project/pull/185983