From ba7f20ac573cc811b59b3aa621912ecf71b0d7a9 Mon Sep 17 00:00:00 2001
From: Scott McKay <skottmckay@gmail.com>
Date: Fri, 13 Oct 2023 08:27:15 +1000
Subject: [PATCH] Fix illegal opcode error from mlas (#17885)

### Description
<!-- Describe your changes. -->
Use cpuinfo value when checking to dot product is available. Reading the
ID_AA64ISAR0_EL1 register is unsafe.

### Motivation and Context
<!-- - Why is this change required? What problem does it solve?
- If it fixes an open issue, please link to the issue here. -->
#17647
#17541
#17851
---
 onnxruntime/core/mlas/lib/platform.cpp | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/onnxruntime/core/mlas/lib/platform.cpp b/onnxruntime/core/mlas/lib/platform.cpp
index 96bc1d8010bed..3c0f82408179b 100644
--- a/onnxruntime/core/mlas/lib/platform.cpp
+++ b/onnxruntime/core/mlas/lib/platform.cpp
@@ -458,12 +458,16 @@ Return Value:
 
 #if defined(_WIN32)
     HasDotProductInstructions = (IsProcessorFeaturePresent(PF_ARM_V82_DP_INSTRUCTIONS_AVAILABLE) != 0);
-#elif !defined(__APPLE__)  // The next few lines result in an EXC_BAD_INSTRUCTION runtime error on a M1 Mac so we
-                           // disable it there.
-    uint64_t isar0_el1;
-    asm("mrs %[reg], ID_AA64ISAR0_EL1\n" : [reg] "=r"(isar0_el1) : :);
-    HasDotProductInstructions = ((isar0_el1 >> 44) & 0xfu) == 0x1u;
 #else
+    // Use the cpuinfo value which is read from sysctl and has some additional special cases.
+    // https://github.com/pytorch/cpuinfo/blob/959002f82d7962a473d8bf301845f2af720e0aa4/src/arm/mach/init.c#L369-L379
+    // Do NOT use ID_AA64ISAR0_EL1. It causes illegal instruction errors on Mac M1 and ARMv8-A chips
+    // as well as failing on other ARM chips as it is an EL1 level register that requires extra
+    // privileges to read.
+    //
+    // uint64_t isar0_el1;
+    // asm("mrs %[reg], ID_AA64ISAR0_EL1\n" : [reg] "=r"(isar0_el1) : :);
+    // HasDotProductInstructions = ((isar0_el1 >> 44) & 0xfu) == 0x1u;
     HasDotProductInstructions = MLAS_CPUIDINFO::GetCPUIDInfo().HasArmNeonDot();
 #endif