[AArch64] Add v8.5 Branch Target Identification support.

The .note.gnu.property must be in the assembly file to indicate the
support for BTI otherwise BTI will be disabled for the whole library.
__unw_getcontext and libunwind::Registers_arm64::jumpto() may be called
indirectly therefore they should start with a landing pad.

Reviewed By: tamas.petz, #libunwind, compnerd

Differential Revision: https://reviews.llvm.org/D77786

diff --git a/libunwind/src/assembly.h b/libunwind/src/assembly.h
index 4cf179e..3b1e6e6 100644 (file)
--- a/libunwind/src/assembly.h
+++ b/libunwind/src/assembly.h
@@ -48,6 +48,24 @@
 #define PPC64_OPD2
 #endif
 
+#if defined(__ARM_FEATURE_BTI_DEFAULT)
+  .pushsection ".note.gnu.property", "a" SEPARATOR                             \
+  .balign 8 SEPARATOR                                                          \
+  .long 4 SEPARATOR                                                            \
+  .long 0x10 SEPARATOR                                                         \
+  .long 0x5 SEPARATOR                                                          \
+  .asciz "GNU" SEPARATOR                                                       \
+  .long 0xc0000000 SEPARATOR /* GNU_PROPERTY_AARCH64_FEATURE_1_AND */          \
+  .long 4 SEPARATOR                                                            \
+  .long 3 SEPARATOR /* GNU_PROPERTY_AARCH64_FEATURE_1_BTI AND */               \
+                    /* GNU_PROPERTY_AARCH64_FEATURE_1_PAC */                   \
+  .long 0 SEPARATOR                                                            \
+  .popsection SEPARATOR
+#define AARCH64_BTI  bti c
+#else
+#define AARCH64_BTI
+#endif
+
 #define GLUE2(a, b) a ## b
 #define GLUE(a, b) GLUE2(a, b)
 #define SYMBOL_NAME(name) GLUE(__USER_LABEL_PREFIX__, name)
@@ -144,7 +162,8 @@
   SYMBOL_IS_FUNC(SYMBOL_NAME(name)) SEPARATOR                                  \
   PPC64_OPD1                                                                   \
   SYMBOL_NAME(name):                                                           \
-  PPC64_OPD2
+  PPC64_OPD2                                                                   \
+  AARCH64_BTI
 
 #if defined(__arm__)
 #if !defined(__ARM_ARCH)