[libc][stdio] implement rename via SYS_renameat2

[nickdesaulniers]

SYS_rename may be unavailable on architectures such as aarch64 and riscv.
rename can be implemented in terms of SYS_rename, SYS_renameat, or
SYS_renameat2. I don't have a full picture of the history here, but it seems
that SYS_renameat might also be unavailable on some platforms.

man 2 rename mentions that SYS_renameat2 was added in Linux 3.15. We don't
need to support such ancient kernel versions prior.

Link: #84980
Link: #85068

[nickdesaulniers]

cc @aniplcc

[llvmbot]

@llvm/pr-subscribers-libc

Author: Nick Desaulniers (nickdesaulniers)

Changes

SYS_rename may be unavailable on architectures such as aarch64 and riscv.
rename can be implemented in terms of SYS_rename, SYS_renameat, or
SYS_renameat2. I don't have a full picture of the history here, but it seems
that SYS_renameat might also be unavailable on some platforms.

man 2 rename mentions that SYS_renameat2 was added in Linux 3.15. We don't
need to support such ancient kernel versions.

Link: #84980
Link: #85068

---

Full diff: https://github.com/llvm/llvm-project/pull/86140.diff

1 Files Affected:

• (modified) libc/src/stdio/linux/rename.cpp (+2-1)

diff --git a/libc/src/stdio/linux/rename.cpp b/libc/src/stdio/linux/rename.cpp
index f3d684249ad28e..afa025864fb1c5 100644
--- a/libc/src/stdio/linux/rename.cpp
+++ b/libc/src/stdio/linux/rename.cpp
@@ -6,6 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "include/llvm-libc-macros/linux/fcntl-macros.h"
 #include "src/stdio/rename.h"
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
@@ -15,7 +16,7 @@
 namespace LIBC_NAMESPACE {
 
 LLVM_LIBC_FUNCTION(int, rename, (const char *oldpath, const char *newpath)) {
-  int ret = LIBC_NAMESPACE::syscall_impl<int>(SYS_rename, oldpath, newpath);
+  int ret = LIBC_NAMESPACE::syscall_impl<int>(SYS_renameat2, AT_FDCWD, oldpath, AT_FDCWD, newpath, 0);
 
   if (ret >= 0)
     return 0;

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[nickdesaulniers]

https://www.kernel.org/doc/html/next/process/adding-syscalls.html#designing-the-api-planning-for-extension mentions:

A new system call forms part of the API of the kernel, and has to be supported indefinitely. As such, it's a very good idea to explicitly discuss the interface on the kernel mailing list, and it's important to plan for future extensions of the interface.

(The syscall table is littered with historical examples where this wasn't done, together with the corresponding follow-up system calls -- eventfd/eventfd2, dup2/dup3, inotify_init/inotify_init1, pipe/pipe2, renameat/renameat2 -- so learn from the history of the kernel and plan for extensions from the start.)

(emphasis added)

[nickdesaulniers]

Merging this to unbreak the build. @michaelrj-google when you're online let's chat about what to do for cases like this in the future. I'm happy to write up public docs for whatever policy we decide on.