[libunwind] 94b475d - [libunwind] Add SME detection for Apple platforms (#193630)

[via cfe-commits]

Author: Brad Smith
Date: 2026-05-05T02:25:33Z
New Revision: 94b475dae69cecf8f80a0936a7510be1c6fdbead

URL: https://github.com/llvm/llvm-project/commit/94b475dae69cecf8f80a0936a7510be1c6fdbead
DIFF: https://github.com/llvm/llvm-project/commit/94b475dae69cecf8f80a0936a7510be1c6fdbead.diff

LOG: [libunwind] Add SME detection for Apple platforms (#193630)

Copy SME detection sysctl code from ZA test. Also fix a
logic issue in the original code while being reviewed.

Added: 
    

Modified: 
    libunwind/src/Registers.hpp
    libunwind/test/aarch64_za_unwind.pass.cpp

Removed: 
    


################################################################################
diff  --git a/libunwind/src/Registers.hpp b/libunwind/src/Registers.hpp
index a7684e2624e75..c88422a6d5f4f 100644
--- a/libunwind/src/Registers.hpp
+++ b/libunwind/src/Registers.hpp
@@ -20,6 +20,9 @@
 #include "libunwind_ext.h"
 #include "shadow_stack_unwind.h"
 
+#if defined(__APPLE__)
+#include <sys/sysctl.h>
+#endif
 #if defined(_LIBUNWIND_HAVE_GETAUXVAL) || defined(_LIBUNWIND_HAVE_ELF_AUX_INFO)
 #include <sys/auxv.h>
 #endif
@@ -1940,7 +1943,15 @@ class _LIBUNWIND_HIDDEN Registers_arm64 {
       _LIBUNWIND_ABORT("SME ZA disable failed");
   }
 
-#if defined(_LIBUNWIND_HAVE_GETAUXVAL)
+#if defined(__APPLE__)
+  static bool checkHasSME() {
+    int has_sme = 0;
+    size_t size = sizeof(has_sme);
+    if (sysctlbyname("hw.optional.arm.FEAT_SME", &has_sme, &size, NULL, 0))
+      return false;
+    return has_sme != 0;
+  }
+#elif defined(_LIBUNWIND_HAVE_GETAUXVAL)
   static bool checkHasSME() {
     constexpr int hwcap2_sme = (1 << 23);
     unsigned long hwcap2 = getauxval(AT_HWCAP2);

diff  --git a/libunwind/test/aarch64_za_unwind.pass.cpp b/libunwind/test/aarch64_za_unwind.pass.cpp
index 84be24d7d2c0a..36536860c1a96 100644
--- a/libunwind/test/aarch64_za_unwind.pass.cpp
+++ b/libunwind/test/aarch64_za_unwind.pass.cpp
@@ -29,7 +29,7 @@
 static bool checkHasSME() {
   int has_sme = 0;
   size_t size = sizeof(has_sme);
-  if (!sysctlbyname("hw.optional.arm.FEAT_SME", &has_sme, &size, NULL, 0))
+  if (sysctlbyname("hw.optional.arm.FEAT_SME", &has_sme, &size, NULL, 0))
     return false;
   return has_sme != 0;
 }