Split CPU feature detection code

Formerly the ARM code favored CPU probes with SIGILLs. We've found its ineffiient on most platforms and dangerous on Apple platforms. This commit splits feature probes into CPU_QueryXXX(), which asks the OS if a feature is present. The detection code then falls back to CPU_ProbeXXX() using SIGILLs as a last resort.

cpu.cpp

@@ -14,8 +14,8 @@
 #include "stdcpp.h"
 
 #ifdef CRYPTOPP_GNU_STYLE_INLINE_ASSEMBLY
-#include <signal.h>
+# include <signal.h>
-#include <setjmp.h>
+# include <setjmp.h>
 #endif
 
 NAMESPACE_BEGIN(CryptoPP)
@@ -26,11 +26,13 @@ extern "C" {
 };
 #endif  // Not CRYPTOPP_MS_STYLE_INLINE_ASSEMBLY
 
+// ***************** IA-32 CPUs ********************
+
 #ifdef CRYPTOPP_CPUID_AVAILABLE
 
 #if _MSC_VER >= 1500
 
-static inline bool CpuId(word32 func, word32 subfunc, word32 output[4])
+inline bool CpuId(word32 func, word32 subfunc, word32 output[4])
 {
 	__cpuidex((int *)output, func, subfunc);
 	return true;
@@ -38,7 +40,7 @@ static inline bool CpuId(word32 func, word32 subfunc, word32 output[4])
 
 #elif _MSC_VER >= 1400 && CRYPTOPP_BOOL_X64
 
-static inline bool CpuId(word32 func, word32 subfunc, word32 output[4])
+inline bool CpuId(word32 func, word32 subfunc, word32 output[4])
 {
 	if (subfunc != 0)
 		return false;
@@ -66,7 +68,7 @@ extern "C"
 }
 #endif
 
-static inline bool CpuId(word32 func, word32 subfunc, word32 output[4])
+inline bool CpuId(word32 func, word32 subfunc, word32 output[4])
 {
 #if defined(CRYPTOPP_MS_STYLE_INLINE_ASSEMBLY)
     __try
@@ -139,7 +141,7 @@ static inline bool CpuId(word32 func, word32 subfunc, word32 output[4])
 
 #endif
 
-static bool TrySSE2()
+static bool CPU_ProbeSSE2()
 {
 #if CRYPTOPP_BOOL_X64
 	return true;
@@ -238,7 +240,7 @@ void DetectX86Features()
 		return;
 
 	if ((cpuid1[3] & (1 << 26)) != 0)
-		g_hasSSE2 = TrySSE2();
+		g_hasSSE2 = CPU_ProbeSSE2();
 	g_hasSSSE3 = g_hasSSE2 && (cpuid1[2] & (1<<9));
 	g_hasSSE41 = g_hasSSE2 && (cpuid1[2] & (1<<19));
 	g_hasSSE42 = g_hasSSE2 && (cpuid1[2] & (1<<20));
@@ -310,43 +312,196 @@ void DetectX86Features()
 	g_x86DetectionDone = true;
 }
 
+// ***************** ARM-32, Aarch32 and Aarch64 CPUs ********************
+
 #elif (CRYPTOPP_BOOL_ARM32 || CRYPTOPP_BOOL_ARM64)
 
-// The ARM equivalent of CPUID probing is reading a MSR. The code requires Exception Level 1 (EL1)
+#if defined(__linux__)
-//   and above, but user space runs at EL0. Attempting to run the code results in a SIGILL and termination.
+# include <sys/auxv.h>
-//
+# ifndef HWCAP_ASIMD
-//     #if defined(__arm64__) || defined(__aarch64__)
+# define HWCAP_ASIMD (1 << 1)
-//	     word64 caps = 0;  // Read ID_AA64ISAR0_EL1
+# endif
-//	     __asm __volatile("mrs %0, " "id_aa64isar0_el1" : "=r" (caps));
+# ifndef HWCAP_ARM_NEON
-//     #elif defined(__arm__) || defined(__aarch32__)
+# define HWCAP_ARM_NEON 4096
-//	     word32 caps = 0;  // Read ID_ISAR5_EL1
+# endif
-//	     __asm __volatile("mrs %0, " "id_isar5_el1" : "=r" (caps));
+# ifndef HWCAP_CRC32
-//     #endif
+# define HWCAP_CRC32 (1 << 7)
-//
+# endif
-// The following does not work well either. Its appears to be missing constants, and it does not detect
+# ifndef HWCAP2_CRC32
-//   Aarch32 execution environments on Aarch64
+# define HWCAP2_CRC32 (1 << 4)
-//   http://community.arm.com/groups/android-community/blog/2014/10/10/runtime-detection-of-cpu-features-on-an-armv8-a-cpu
+# endif
-//
+# ifndef HWCAP_PMULL
+# define HWCAP_PMULL (1 << 4)
+# endif
+# ifndef HWCAP2_PMULL
+# define HWCAP2_PMULL (1 << 1)
+# endif
+# ifndef HWCAP_AES
+# define HWCAP_AES (1 << 3)
+# endif
+# ifndef HWCAP2_AES
+# define HWCAP2_AES (1 << 0)
+# endif
+# ifndef HWCAP_SHA1
+# define HWCAP_SHA1 (1 << 5)
+# endif
+# ifndef HWCAP_SHA2
+# define HWCAP_SHA2 (1 << 6)
+# endif
+# ifndef HWCAP2_SHA1
+# define HWCAP2_SHA1 (1 << 2)
+# endif
+# ifndef HWCAP2_SHA2
+# define HWCAP2_SHA2 (1 << 3)
+# endif
+#endif
+
+#if defined(__APPLE__) && defined(__aarch64__)
+# include <sys/utsname.h>
+#endif
+
 bool CRYPTOPP_SECTION_INIT g_ArmDetectionDone = false;
 bool CRYPTOPP_SECTION_INIT g_hasNEON = false, CRYPTOPP_SECTION_INIT g_hasPMULL = false, CRYPTOPP_SECTION_INIT g_hasCRC32 = false;
 bool CRYPTOPP_SECTION_INIT g_hasAES = false, CRYPTOPP_SECTION_INIT g_hasSHA1 = false, CRYPTOPP_SECTION_INIT g_hasSHA2 = false;
 word32 CRYPTOPP_SECTION_INIT g_cacheLineSize = CRYPTOPP_L1_CACHE_LINE_SIZE;
 
-extern bool CPU_TryNEON_ARM();
+// ARM does not have an unprivliged equivalent to CPUID on IA-32. We have to jump through some
-extern bool CPU_TryAES_ARMV8();
+//   hoops to detect features on a wide array of platforms. Our strategy is two part. First,
-extern bool CPU_TrySHA1_ARMV8();
+//   attempt to *Query* the OS for a feature, like using getauxval on Linux. If that fails,
-extern bool CPU_TrySHA2_ARMV8();
+//   then *Probe* the cpu executing an instruction and an observe a SIGILL if unsupported.
-extern bool CPU_TryCRC32_ARMV8();
+// The probes are in source files where compilation options like -march=armv8-a+crc make
-extern bool CPU_TryPMULL_ARMV8();
+//   intrinsics available. They are expensive when compared to a standard OS feature query.
+//   Always perform the feature quesry first. For Linux see
+//   http://sourceware.org/ml/libc-help/2017-08/msg00012.html
+// Avoid probes on Apple platforms because Apple's signal handling for SIGILLs appears broken.
+//   We are trying to figure out a way to feature test without probes. Also see
+//   http://stackoverflow.com/a/11197770/608639 and
+//   http://gist.github.com/erkanyildiz/390a480f27e86f8cd6ba
+
+extern bool CPU_ProbeNEON();
+extern bool CPU_ProbeCRC32();
+extern bool CPU_ProbeAES();
+extern bool CPU_ProbeSHA1();
+extern bool CPU_ProbeSHA2();
+extern bool CPU_ProbePMULL();
+
+inline bool CPU_QueryNEON()
+{
+#if defined(__ANDROID__) && (defined(__aarch32__) || defined(__aarch64__))
+	if (android_getCpuFeatures() & ANDROID_CPU_ARM64_FEATURE_ASIMD)
+		return true;
+#elif defined(__ANDROID__) && defined(__arm__)
+	if (android_getCpuFeatures() & ANDROID_CPU_ARM_FEATURE_NEON)
+		return true;
+#elif defined(__linux__) && defined(__aarch64__)
+	if (getauxval(AT_HWCAP) & HWCAP_ASIMD)
+		return true;
+#elif defined(__linux__) && defined(__aarch32__)
+	if (getauxval(AT_HWCAP2) & HWCAP2_ASIMD)
+		return true;
+#elif defined(__linux__) && defined(__arm__)
+	if (getauxval(AT_HWCAP) & HWCAP_ARM_NEON)
+		return true;
+#endif
+	return false;
+}
+
+inline bool CPU_QueryCRC32()
+{
+#if defined(__ANDROID__) && (defined(__aarch64__) || defined(__aarch32__))
+	if (android_getCpuFeatures() & ANDROID_CPU_ARM64_FEATURE_CRC32)
+		return true;
+#elif defined(__linux__) && defined(__aarch64__)
+	if (getauxval(AT_HWCAP) & HWCAP_CRC32)
+		return true;
+#elif defined(__linux__) && defined(__aarch32__)
+	if (getauxval(AT_HWCAP2) & HWCAP2_CRC32)
+		return true;
+#endif
+	return false;
+}
+
+inline bool CPU_QueryPMULL()
+{
+#if defined(__ANDROID__) && (defined(__aarch64__) || defined(__aarch32__))
+	if (android_getCpuFeatures() & ANDROID_CPU_ARM64_FEATURE_PMULL)
+		return true;
+#elif defined(__linux__) && defined(__aarch64__)
+	if (getauxval(AT_HWCAP) & HWCAP_PMULL)
+		return true;
+#elif defined(__linux__) && defined(__aarch32__)
+	if (getauxval(AT_HWCAP2) & HWCAP2_PMULL)
+		return true;
+#endif
+	return false;
+}
+
+inline bool CPU_QueryAES()
+{
+#if defined(__ANDROID__) && (defined(__aarch64__) || defined(__aarch32__))
+	if (android_getCpuFeatures() & ANDROID_CPU_ARM64_FEATURE_AES)
+		return true;
+#elif defined(__linux__) && defined(__aarch64__)
+	if (getauxval(AT_HWCAP) & HWCAP_AES)
+		return true;
+#elif defined(__linux__) && defined(__aarch32__)
+	if (getauxval(AT_HWCAP2) & HWCAP2_AES)
+		return true;
+#elif defined(__APPLE__)
+	struct utsname systemInfo;
+	systemInfo.machine[0] = '\0';
+	uname(&systemInfo);
+
+	std::string machine(systemInfo.machine);
+	if (machine.substr(0, 7) == "iPhone6" || machine.substr(0, 7) == "iPhone7" ||
+		machine.substr(0, 7) == "iPhone8" || machine.substr(0, 7) == "iPhone9" ||
+		machine.substr(0, 5) == "iPad4" || machine.substr(0, 5) == "iPad5" ||
+		machine.substr(0, 5) == "iPad6" || machine.substr(0, 5) == "iPad7")
+	{
+		return true;
+	}
+#endif
+	return false;
+}
+
+inline bool CPU_QuerySHA1()
+{
+#if defined(__ANDROID__) && (defined(__aarch64__) || defined(__aarch32__))
+	if (android_getCpuFeatures() & ANDROID_CPU_ARM64_FEATURE_SHA1)
+		return true;
+#elif defined(__linux__) && defined(__aarch64__)
+	if (getauxval(AT_HWCAP) & HWCAP_SHA1)
+		return true;
+#elif defined(__linux__) && defined(__aarch32__)
+	if (getauxval(AT_HWCAP2) & HWCAP2_SHA1)
+		return true;
+#endif
+	return false;
+}
+
+inline bool CPU_QuerySHA2()
+{
+#if defined(__ANDROID__) && (defined(__aarch64__) || defined(__aarch32__))
+	if (android_getCpuFeatures() & ANDROID_CPU_ARM64_FEATURE_SHA2)
+		return true;
+#elif defined(__linux__) && defined(__aarch64__)
+	if (getauxval(AT_HWCAP) & HWCAP_SHA2)
+		return true;
+#elif defined(__linux__) && defined(__aarch32__)
+	if (getauxval(AT_HWCAP2) & HWCAP2_SHA2)
+		return true;
+#endif
+	return false;
+}
 
 void DetectArmFeatures()
 {
-	g_hasNEON = CPU_TryNEON_ARM();
+	g_hasNEON  = CPU_QueryNEON() || CPU_ProbeNEON();
-	g_hasPMULL = CPU_TryPMULL_ARMV8();
+	g_hasCRC32 = CPU_QueryCRC32() || CPU_ProbeCRC32();
-	g_hasCRC32 = CPU_TryCRC32_ARMV8();
+	g_hasPMULL = CPU_QueryPMULL() || CPU_ProbePMULL();
-	g_hasAES = CPU_TryAES_ARMV8();
+	g_hasAES  = CPU_QueryAES() || CPU_ProbeAES();
-	g_hasSHA1 = CPU_TrySHA1_ARMV8();
+	g_hasSHA1 = CPU_QuerySHA1() || CPU_ProbeSHA1();
-	g_hasSHA2 = CPU_TrySHA2_ARMV8();
+	g_hasSHA2 = CPU_QuerySHA2() || CPU_ProbeSHA2();
 
 	g_ArmDetectionDone = true;
 }

crc-simd.cpp

@@ -15,16 +15,6 @@
 # undef CRYPTOPP_ARM_CRC32_AVAILABLE
 #endif
 
-#if defined(__linux__)
-# include <sys/auxv.h>
-# ifndef HWCAP_CRC32
-# define HWCAP_CRC32 (1 << 7)
-# endif
-# ifndef HWCAP2_CRC32
-# define HWCAP2_CRC32 (1 << 4)
-# endif
-#endif
-
 #if (CRYPTOPP_SSE42_AVAILABLE)
 # include "nmmintrin.h"
 #endif
@@ -61,7 +51,7 @@ extern "C" {
 
 #if (CRYPTOPP_BOOL_ARM32 || CRYPTOPP_BOOL_ARM64)
 
-bool CPU_TryCRC32_ARMV8()
+bool CPU_ProbeCRC32()
 {
 #if (CRYPTOPP_ARM_CRC32_AVAILABLE)
 # if defined(CRYPTOPP_MS_STYLE_INLINE_ASSEMBLY)
@@ -84,17 +74,6 @@ bool CPU_TryCRC32_ARMV8()
     }
     return result;
 #else
-#   if defined(__ANDROID__) && (defined(__aarch64__) || defined(__aarch32__))
-    if (android_getCpuFeatures() & ANDROID_CPU_ARM64_FEATURE_CRC32)
-		return true;
-    // https://sourceware.org/ml/libc-help/2017-08/msg00012.html
-#   elif defined(__linux__) && defined(__aarch64__)
-	if (getauxval(AT_HWCAP) & HWCAP_CRC32)
-		return true;
-#   elif defined(__linux__) && defined(__aarch32__)
-	if (getauxval(AT_HWCAP2) & HWCAP2_CRC32)
-		return true;
-#   endif
 
     // longjmp and clobber warnings. Volatile is required.
     // http://github.com/weidai11/cryptopp/issues/24 and http://stackoverflow.com/q/7721854

gcm-simd.cpp

@@ -24,16 +24,6 @@
 # undef CRYPTOPP_ARM_PMULL_AVAILABLE
 #endif
 
-#if defined(__linux__)
-# include <sys/auxv.h>
-# ifndef HWCAP_PMULL
-# define HWCAP_PMULL (1 << 4)
-# endif
-# ifndef HWCAP2_PMULL
-# define HWCAP2_PMULL (1 << 1)
-# endif
-#endif
-
 #if (CRYPTOPP_CLMUL_AVAILABLE)
 # include "tmmintrin.h"
 # include "wmmintrin.h"
@@ -203,7 +193,7 @@ extern "C" {
 #endif  // Not CRYPTOPP_MS_STYLE_INLINE_ASSEMBLY
 
 #if (CRYPTOPP_BOOL_ARM32 || CRYPTOPP_BOOL_ARM64)
-bool CPU_TryPMULL_ARMV8()
+bool CPU_ProbePMULL()
 {
 #if (CRYPTOPP_ARM_PMULL_AVAILABLE)
 # if defined(CRYPTOPP_MS_STYLE_INLINE_ASSEMBLY)
@@ -230,17 +220,6 @@ bool CPU_TryPMULL_ARMV8()
     }
     return result;
 # else
-#   if defined(__ANDROID__) && (defined(__aarch64__) || defined(__aarch32__))
-    if (android_getCpuFeatures() & ANDROID_CPU_ARM64_FEATURE_PMULL)
-        return true;
-    // https://sourceware.org/ml/libc-help/2017-08/msg00012.html
-#   elif defined(__linux__) && defined(__aarch64__)
-    if (getauxval(AT_HWCAP) & HWCAP_PMULL)
-        return true;
-#   elif defined(__linux__) && defined(__aarch32__)
-    if (getauxval(AT_HWCAP2) & HWCAP2_PMULL)
-        return true;
-#   endif
 
     // longjmp and clobber warnings. Volatile is required.
     // http://github.com/weidai11/cryptopp/issues/24 and http://stackoverflow.com/q/7721854

neon.cpp

@@ -8,17 +8,6 @@
 
 #include "pch.h"
 #include "config.h"
-#include "stdcpp.h"
-
-#if defined(__linux__)
-# include <sys/auxv.h>
-# ifndef HWCAP_ASIMD
-# define HWCAP_ASIMD (1 << 1)
-# endif
-# ifndef HWCAP_ARM_NEON
-# define HWCAP_ARM_NEON 4096
-# endif
-#endif
 
 #if (CRYPTOPP_ARM_NEON_AVAILABLE)
 # include "arm_neon.h"
@@ -47,7 +36,7 @@ extern "C" {
 };
 #endif  // Not CRYPTOPP_MS_STYLE_INLINE_ASSEMBLY
 
-bool CPU_TryNEON_ARM()
+bool CPU_ProbeNEON()
 {
 #if (CRYPTOPP_ARM_NEON_AVAILABLE)
 # if defined(CRYPTOPP_MS_STYLE_INLINE_ASSEMBLY)
@@ -74,22 +63,6 @@ bool CPU_TryNEON_ARM()
 	}
 	return result;
 # else
-#   if defined(__ANDROID__) && (defined(__aarch32__) || defined(__aarch64__))
-	if (android_getCpuFeatures() & ANDROID_CPU_ARM64_FEATURE_ASIMD)
-		return true;
-#   elif defined(__ANDROID__) && defined(__arm__)
-	if (android_getCpuFeatures() & ANDROID_CPU_ARM_FEATURE_NEON)
-		return true;
-#   elif defined(__linux__) && defined(__aarch64__)
-	if (getauxval(AT_HWCAP) & HWCAP_ASIMD)
-		return true;
-#   elif defined(__linux__) && defined(__aarch32__)
-	if (getauxval(AT_HWCAP2) & HWCAP2_ASIMD)
-		return true;
-#   elif defined(__linux__) && defined(__arm__)
-	if (getauxval(AT_HWCAP) & HWCAP_ARM_NEON)
-		return true;
-#   endif
 
 	// longjmp and clobber warnings. Volatile is required.
 	// http://github.com/weidai11/cryptopp/issues/24 and http://stackoverflow.com/q/7721854

rijndael-simd.cpp

@@ -20,16 +20,6 @@
 # undef CRYPTOPP_ARM_AES_AVAILABLE
 #endif
 
-#if defined(__linux__)
-# include <sys/auxv.h>
-# ifndef HWCAP_AES
-# define HWCAP_AES (1 << 3)
-# endif
-# ifndef HWCAP2_AES
-# define HWCAP2_AES (1 << 0)
-# endif
-#endif
-
 #if (CRYPTOPP_AESNI_AVAILABLE)
 // Hack... We are supposed to use <nmmintrin.h>. GCC 4.8, LLVM Clang 3.5
 //   and Apple Clang 6.0 conflates SSE4.1 and SSE4.2. If we use <nmmintrin.h>
@@ -55,10 +45,6 @@
 # include <setjmp.h>
 #endif
 
-#if defined(__APPLE__) && defined(__aarch64__)
-# include <sys/utsname.h>
-#endif
-
 #ifndef EXCEPTION_EXECUTE_HANDLER
 # define EXCEPTION_EXECUTE_HANDLER 1
 #endif
@@ -89,7 +75,7 @@ extern "C" {
 #endif  // Not CRYPTOPP_MS_STYLE_INLINE_ASSEMBLY
 
 #if (CRYPTOPP_BOOL_ARM32 || CRYPTOPP_BOOL_ARM64)
-bool CPU_TryAES_ARMV8()
+bool CPU_ProbeAES()
 {
 #if (CRYPTOPP_ARM_AES_AVAILABLE)
 # if defined(CRYPTOPP_MS_STYLE_INLINE_ASSEMBLY)
@@ -111,35 +97,6 @@ bool CPU_TryAES_ARMV8()
 	}
 	return result;
 # else
-#   if defined(__ANDROID__) && (defined(__aarch64__) || defined(__aarch32__))
-    if (android_getCpuFeatures() & ANDROID_CPU_ARM64_FEATURE_AES)
-		return true;
-    // https://sourceware.org/ml/libc-help/2017-08/msg00012.html
-#   elif defined(__linux__) && defined(__aarch64__)
-	if (getauxval(AT_HWCAP) & HWCAP_AES)
-		return true;
-#   elif defined(__linux__) && defined(__aarch32__)
-	if (getauxval(AT_HWCAP2) & HWCAP2_AES)
-		return true;
-#   elif defined(__APPLE__)
-    {
-		// https://stackoverflow.com/a/11197770/608639
-		// https://gist.github.com/erkanyildiz/390a480f27e86f8cd6ba
-		struct utsname systemInfo;
-		systemInfo.machine[0] = '\0';
-		uname(&systemInfo);
-
-		std::string machine(systemInfo.machine);
-
-		if (machine.substr(0, 7) == "iPhone6" || machine.substr(0, 7) == "iPhone7" ||
-			machine.substr(0, 7) == "iPhone8" || machine.substr(0, 7) == "iPhone9" ||
-			machine.substr(0, 5) == "iPad4" || machine.substr(0, 5) == "iPad5" ||
-			machine.substr(0, 5) == "iPad6" || machine.substr(0, 5) == "iPad7")
-		{
-			return true;
-		}
-	}
-#   endif
 
 	// longjmp and clobber warnings. Volatile is required.
 	// http://github.com/weidai11/cryptopp/issues/24 and http://stackoverflow.com/q/7721854

sha-simd.cpp

@@ -16,22 +16,6 @@
 # undef CRYPTOPP_ARM_SHA_AVAILABLE
 #endif
 
-#if defined(__linux__)
-# include <sys/auxv.h>
-# ifndef HWCAP_SHA1
-# define HWCAP_SHA1 (1 << 5)
-# endif
-# ifndef HWCAP_SHA2
-# define HWCAP_SHA2 (1 << 6)
-# endif
-# ifndef HWCAP2_SHA1
-# define HWCAP2_SHA1 (1 << 2)
-# endif
-# ifndef HWCAP2_SHA2
-# define HWCAP2_SHA2 (1 << 3)
-# endif
-#endif
-
 #if (CRYPTOPP_SHANI_AVAILABLE)
 # include "nmmintrin.h"
 # include "immintrin.h"
@@ -76,7 +60,7 @@ extern "C" {
 #endif  // Not CRYPTOPP_MS_STYLE_INLINE_ASSEMBLY
 
 #if (CRYPTOPP_BOOL_ARM32 || CRYPTOPP_BOOL_ARM64)
-bool CPU_TrySHA1_ARMV8()
+bool CPU_ProbeSHA1()
 {
 #if (CRYPTOPP_ARM_SHA_AVAILABLE)
 # if defined(CRYPTOPP_MS_STYLE_INLINE_ASSEMBLY)
@@ -99,17 +83,6 @@ bool CPU_TrySHA1_ARMV8()
     }
     return result;
 # else
-#   if defined(__ANDROID__) && (defined(__aarch64__) || defined(__aarch32__))
-    if (android_getCpuFeatures() & ANDROID_CPU_ARM64_FEATURE_SHA1)
-        return true;
-    // https://sourceware.org/ml/libc-help/2017-08/msg00012.html
-#   elif defined(__linux__) && defined(__aarch64__)
-    if (getauxval(AT_HWCAP) & HWCAP_SHA1)
-        return true;
-#   elif defined(__linux__) && defined(__aarch32__)
-    if (getauxval(AT_HWCAP2) & HWCAP2_SHA1)
-        return true;
-#   endif
 
     // longjmp and clobber warnings. Volatile is required.
     // http://github.com/weidai11/cryptopp/issues/24 and http://stackoverflow.com/q/7721854
@@ -147,7 +120,7 @@ bool CPU_TrySHA1_ARMV8()
 #endif  // CRYPTOPP_ARM_SHA_AVAILABLE
 }
 
-bool CPU_TrySHA2_ARMV8()
+bool CPU_ProbeSHA2()
 {
 #if (CRYPTOPP_ARM_SHA_AVAILABLE)
 # if defined(CRYPTOPP_MS_STYLE_INLINE_ASSEMBLY)
@@ -169,17 +142,6 @@ bool CPU_TrySHA2_ARMV8()
     }
     return result;
 #else
-#   if defined(__ANDROID__) && (defined(__aarch64__) || defined(__aarch32__))
-    if (android_getCpuFeatures() & ANDROID_CPU_ARM64_FEATURE_SHA2)
-        return true;
-    // https://sourceware.org/ml/libc-help/2017-08/msg00012.html
-#   elif defined(__linux__) && defined(__aarch64__)
-    if (getauxval(AT_HWCAP) & HWCAP_SHA2)
-        return true;
-#   elif defined(__linux__) && defined(__aarch32__)
-    if (getauxval(AT_HWCAP2) & HWCAP2_SHA2)
-        return true;
-#   endif
 
     // longjmp and clobber warnings. Volatile is required.
     // http://github.com/weidai11/cryptopp/issues/24 and http://stackoverflow.com/q/7721854