ebb3309975
This patch initiates the refactoring of Linux syscalls as described in the RFC (https://discourse.llvm.org/t/rfc-linux-syscall-cleanup/87248/). It introduces a new infrastructure in `src/__support/OSUtil/linux/syscall_wrappers/` to house header-only syscall wrappers. These wrappers utilize `ErrorOr` to provide a consistent, type-safe interface for error handling across the library, standardizing how syscall return values are converted into errno-compatible Error objects. Summary of changes: - Created the `syscall_wrappers` directory and added `close.h`, `read.h`, `write.h`, and `open.h`. - Moved the existing `getrandom.h` into the new `syscall_wrappers` directory and updated its callers (including HashTable/randomness.h). - Refactored core entrypoints (`close`, `read`, `write`, `open`) to use the new wrappers, removing direct `syscall_impl` logic and manual errno setting. - Updated `shm_open.cpp` to use the new `open` wrapper. - Cleaned up `OSUtil/linux/fcntl.cpp` by removing redundant internal implementations of `open` and `close`. - Added a developer guide in `docs/dev/syscall_wrapper_refactor.rst` outlining the established pattern for future migrations. --------- Co-authored-by: Michael Jones <michaelrj@google.com>
76 lines
2.7 KiB
ReStructuredText
76 lines
2.7 KiB
ReStructuredText
.. _syscall_wrapper_refactor:
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==============================
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Syscall Wrapper Refactoring
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==============================
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Purpose
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=======
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LLVM-libc is transitioning to a centralized system for Linux syscalls. The goal
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is to move all direct ``syscall_impl`` calls into a dedicated directory:
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``src/__support/OSUtil/linux/syscall_wrappers/``.
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This refactor provides several benefits:
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* **Reusability**: Allows multiple entrypoints to share a single syscall
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implementation without public APIs depending on other public APIs.
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* **Type Safety**: Using ``ErrorOr<T>`` ensures that error conditions are
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handled explicitly.
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* **Consistency**: Standardizes the conversion of syscall return values into
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errno-compatible objects.
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* **Maintainability**: Centralizes platform-specific syscall logic, making it
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easier to audit and update.
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The Pattern
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===========
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Each syscall should have its own header-only library in the ``syscall_wrappers``
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directory. The wrapper function should return an ``ErrorOr<T>``. Wrappers live
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in the ``linux_syscalls`` namespace to make call sites self-documenting and to
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clearly identify any leakage into OS-generic code.
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Example Wrapper (``src/__support/OSUtil/linux/syscall_wrappers/read.h``):
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--------------------------------------------------------------------------
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.. code-block:: c++
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#include "hdr/types/ssize_t.h"
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#include "src/__support/OSUtil/linux/syscall.h" // For syscall_impl
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#include "src/__support/common.h"
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#include "src/__support/error_or.h"
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#include "src/__support/macros/config.h"
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#include <sys/syscall.h> // For syscall numbers
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namespace LIBC_NAMESPACE_DECL {
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namespace linux_syscalls {
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LIBC_INLINE ErrorOr<ssize_t> read(int fd, void *buf, size_t count) {
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ssize_t ret = syscall_impl<ssize_t>(SYS_read, fd, buf, count);
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if (ret < 0) {
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return Error(-static_cast<int>(ret));
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}
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return ret;
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}
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} // namespace linux_syscalls
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} // namespace LIBC_NAMESPACE_DECL
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How to Migrate
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==============
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1. **Cleanup Existing Implementation**: If the syscall was previously
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implemented in ``OSUtil/linux/fcntl.cpp`` (or similar), remove the old
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implementation to replace it with the new wrapper.
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2. **Create the Wrapper**: Add a new header file in
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``src/__support/OSUtil/linux/syscall_wrappers/``.
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3. **Update CMake**: Add a ``add_header_library`` target for the new wrapper in
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``src/__support/OSUtil/linux/syscall_wrappers/CMakeLists.txt``.
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4. **Refactor Entrypoints**:
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* Include the new wrapper header (e.g., ``read.h``).
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* Replace direct ``syscall_impl`` calls with
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``linux_syscalls::<function_name>``.
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* Update the entrypoint's ``DEPENDS`` in ``CMakeLists.txt`` to include the
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new wrapper target.
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