[libc-commits] [libc] [libc] Implement getcontext and setcontext for x86_64 (PR #192343)

[Pavel Labath via libc-commits]

================
@@ -0,0 +1,86 @@
+//===-- Implementation of setcontext for x86_64 ---------------------------===//
+//
+// 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/ucontext/setcontext.h"
+#include "include/llvm-libc-types/ucontext_t.h"
+#include "src/__support/common.h"
+#include "src/__support/macros/config.h"
+
+#include "hdr/types/size_t.h"
+#include <sys/syscall.h>
+
+namespace LIBC_NAMESPACE_DECL {
+
+__attribute__((naked)) LLVM_LIBC_FUNCTION(int, setcontext,
+                                          (const ucontext_t *ucp)) {
+  asm(R"(
+      # ucp is in rdi
+      
+      # Restore the signal mask using rt_sigprocmask syscall.
+      # rt_sigprocmask(SIG_SETMASK, &ucp->uc_sigmask, NULL, sizeof(sigset_t))
+      pushq %%rdi # Save ucp
----------------
labath wrote:

(optional) Tiny optimization: since the current registers are going to get nuked anyway, you can save rdi into any non-volatile register.

https://github.com/llvm/llvm-project/pull/192343