[compiler-rt] [safestack] store unsafe stack pointer in TCB

[ghost]

I modified the safestack runtime library to store the unsafe stack pointer directly in the TCB. By storing the pointer in the TCB, instead of a thread-local variable, access to the unsafe stack pointer can be faster by eliminating an additional level of indirection.

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[github-actions]

⚠️ C/C++ code formatter, clang-format found issues in your code. ⚠️

You can test this locally with the following command:

git-clang-format --diff e28d3e9b4e5779028a38ca39ed060938ff62c498 1430f4892fb563a54920674284d7de276983c849 -- compiler-rt/lib/safestack/safestack.cpp

View the diff from clang-format here.

diff --git a/compiler-rt/lib/safestack/safestack.cpp b/compiler-rt/lib/safestack/safestack.cpp
index 0f2eab2f12..19e740964a 100644
--- a/compiler-rt/lib/safestack/safestack.cpp
+++ b/compiler-rt/lib/safestack/safestack.cpp
@@ -38,13 +38,13 @@ __attribute__((visibility(
 }
 
 #if defined(__linux__) && defined(__x86_64__)
-#include <stdint.h>
-#include <sys/types.h>
+#  include <stdint.h>
+#  include <sys/types.h>
 
 typedef struct {
-  void *tcb; /* Pointer to the TCB. Not necessarily the
-                thread descriptor used by libpthread. */
-  uint64_t *stack_guard; /* Stack guard value for the thread. */
+  void *tcb;              /* Pointer to the TCB. Not necessarily the
+                             thread descriptor used by libpthread. */
+  uint64_t *stack_guard;  /* Stack guard value for the thread. */
   void *unsafe_stack_ptr; /* Unsafe stack pointer for the thread. */
 } tcbhead_t;