x86_64: Use shadow stack for backtrace implementationfw/x86-shstk-backtrace

Test failures:

FAIL: debug/tst-backtrace4
FAIL: misc/tst-sigcontext-get_pc

The return address of signal handlers is not on the shadow stack.

1 files changed, 62 insertions, 0 deletions

diff --git a/sysdeps/x86_64/arch_backtrace.h b/sysdeps/x86_64/arch_backtrace.h
new file mode 100644
index 0000000..64f173f
--- /dev/null
+++ b/sysdeps/x86_64/arch_backtrace.h
@@ -0,0 +1,62 @@
+/* Architecture-specific backtrace implementation.  x86-64 version.
+   Copyright (C) 2024 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <stdbool.h>
+#include <sysdep.h>
+
+/* From libc_sigaction.c.  */
+extern void restore_rt (void) asm ("__restore_rt") attribute_hidden;
+
+/* Copy addresses from the shadow stack if available.  */
+static inline __always_inline int
+__arch_backtrace (void **array, int size)
+{
+#if CET_ENABLED
+  void **ssp;
+  asm ("rdsspq %0"
+       : "=r" (ssp)
+       : "0" (0));
+  if (ssp == NULL)
+    return -1;
+
+  void **ssp_base = (void **) THREAD_GETMEM (THREAD_SELF, header.ssp_base);
+  if (ssp_base < ssp)
+    /* Covers the NULL case.  */
+    return 0;
+
+  long int limit = ssp_base - ssp;
+  if (limit > size)
+    limit = size;
+
+#if 1
+  __builtin_memcpy (array, ssp, limit * sizeof (*array));
+  return limit;
+#else
+  /* We cannot use memcpy because we need to filter out signal
+     frames.  */
+  int count = 0;
+  for (unsigned int i = 0; i < limit; ++i)
+    if (ssp[i] != restore_rt)
+      array[count++] = ssp[i];
+  return count;
+#endif
+
+#else /* !CET_ENABLED */
+  return -1;
+#endif
+}