fb

src/libraries/Common/src/Interop/Unix/System.Native/Interop.IsQemuDetected.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System.Runtime.InteropServices;
+using System.Threading;
 
 internal static partial class Interop
 {
@@ -11,7 +12,22 @@ internal static partial class Sys
         [return: MarshalAs(UnmanagedType.Bool)]
         private static partial bool IsQemuDetectedImpl();
 
-        private static bool? _isQemuDetected;
-        internal static bool IsQemuDetected() => _isQemuDetected ??= IsQemuDetectedImpl();
+        private static int s_isQemuDetected;
+
+        internal static bool IsQemuDetected()
+        {
+            int isQemuDetected = Interlocked.CompareExchange(ref s_isQemuDetected, 0, 0);
+            if (isQemuDetected == 0)
+            {
+                isQemuDetected = IsQemuDetectedImpl() ? 1 : 2;
+                int oldValue = Interlocked.CompareExchange(ref s_isQemuDetected, isQemuDetected, 0);
+                if (oldValue != 0) // a different thread has managed to update the value
+                {
+                    isQemuDetected = oldValue;
+                }
+            }
+
+            return isQemuDetected == 1;
+        }
     }
 }

src/native/minipal/cpufeatures.c

@@ -231,11 +231,11 @@ int minipal_getcpufeatures(void)
 
                                     if (IsAvx512Enabled() && (avx512StateSupport() == 1))                       // XGETBV XRC0[7:5] == 111
                                     {
-                                        if (((cpuidInfo[CPUID_EBX] & ((uint32_t)1 << 16)) != 0) &&                        // AVX512F
-                                            ((cpuidInfo[CPUID_EBX] & ((uint32_t)1 << 30)) != 0) &&                        // AVX512BW
-                                            ((cpuidInfo[CPUID_EBX] & ((uint32_t)1 << 28)) != 0) &&                        // AVX512CD
-                                            ((cpuidInfo[CPUID_EBX] & ((uint32_t)1 << 17)) != 0) &&                        // AVX512DQ
-                                            ((cpuidInfo[CPUID_EBX] & ((uint32_t)1 << 31)) != 0))                          // AVX512VL
+                                        if ((((uint32_t)cpuidInfo[CPUID_EBX] & ((uint32_t)1 << 16)) != 0) &&                        // AVX512F
+                                            (((uint32_t)cpuidInfo[CPUID_EBX] & ((uint32_t)1 << 30)) != 0) &&                        // AVX512BW
+                                            (((uint32_t)cpuidInfo[CPUID_EBX] & ((uint32_t)1 << 28)) != 0) &&                        // AVX512CD
+                                            (((uint32_t)cpuidInfo[CPUID_EBX] & ((uint32_t)1 << 17)) != 0) &&                        // AVX512DQ
+                                            (((uint32_t)cpuidInfo[CPUID_EBX] & ((uint32_t)1 << 31)) != 0))                          // AVX512VL
                                         {
                                             // While the AVX-512 ISAs can be individually lit-up, they really
                                             // need F, BW, CD, DQ, and VL to be fully functional without adding
@@ -450,48 +450,53 @@ int minipal_getcpufeatures(void)
     return result;
 }
 
-static const char* GetCpuBrand(void)
+static bool GetCpuBrand(char* brand, size_t bufferSize)
 {
 #if defined(HOST_AMD64) || defined(HOST_X86)
     // Check for CPU brand indicating emulation
     int regs[4];
-    static char brand[49];
 
     // Get the maximum value for extended function CPUID info
     __cpuid(regs, (int)0x80000000);
     if ((unsigned int)regs[0] < 0x80000004)
     {
-        return ""; // Extended CPUID not supported, return empty string or handle error
+        brand[0] = '\0'; // Extended CPUID not supported, return empty string or handle error
+        return false;
     }
 
-    // Retrieve the CPU brand string
+    // Retrieve the CPU brand string directly into the caller-provided buffer
     for (unsigned int i = 0x80000002; i <= 0x80000004; ++i)
     {
         __cpuid(regs, (int)i);
         memcpy(brand + (i - 0x80000002) * sizeof(regs), regs, sizeof(regs));
     }
-    brand[sizeof(brand) - 1] = '\0';
 
-    return brand;
+    brand[bufferSize - 1] = '\0';
+
+    return true;
 #else
-    return "";
+    return false;
 #endif // HOST_AMD64 || HOST_X86
 }
 
 // Detect if the current process is running under the Apple Rosetta x64 emulator
 bool minipal_detect_rosetta(void)
 {
+    char brand[49];
+
     // Check if CPU brand indicates emulation
-    return (strstr(GetCpuBrand(), "VirtualApple") != NULL);
+    return GetCpuBrand(brand, sizeof(brand)) && (strstr(brand, "VirtualApple") != NULL);
 }
 
 #if !defined(HOST_WINDOWS)
 
 // Detect if the current process is running under QEMU
 bool minipal_detect_qemu(void)
 {
+    char brand[49];
+
     // Check if CPU brand indicates emulation
-    if (strstr(GetCpuBrand(), "QEMU") != NULL)
+    if (GetCpuBrand(brand, sizeof(brand)) && strstr(brand, "QEMU") != NULL)
     {
         return true;
     }