Add option to change SVE vector length for current and children processes.

TEST_LABEL: ent-arch-aarch64
TEST_IMG: ubuntu/dotnet-build
TEST_CMD: safe ./projects/dotnet/test-runtime.sh --scope coreclr,libs

Jira: ENTLLT-7328

Change-Id: I727edf8652a5c8648e7008d4ca47e7a4f36d5a1e

Author: SwapnilGaikwad

src/coreclr/inc/clrconfigvalues.h

@@ -790,6 +790,10 @@ RETAIL_CONFIG_DWORD_INFO(EXTERNAL_EnableArm64Sha256,            W("EnableArm64Sh
 RETAIL_CONFIG_DWORD_INFO(EXTERNAL_EnableArm64Rcpc,              W("EnableArm64Rcpc"),           1, "Allows Arm64 Rcpc+ hardware intrinsics to be disabled")
 RETAIL_CONFIG_DWORD_INFO(EXTERNAL_EnableArm64Rcpc2,             W("EnableArm64Rcpc2"),          1, "Allows Arm64 Rcpc2+ hardware intrinsics to be disabled")
 RETAIL_CONFIG_DWORD_INFO(EXTERNAL_EnableArm64Sve,               W("EnableArm64Sve"),            1, "Allows Arm64 SVE hardware intrinsics to be disabled")
+#if defined(TARGET_LINUX) && (defined(DEBUG) || defined(_DEBUG))
+// TODO-SVE: Once coreclr supports vector lengths >16bytes, the default should be -1.
+RETAIL_CONFIG_DWORD_INFO_EX(EXTERNAL_MaxVectorLength,           W("MaxVectorLength"),          16, "Specifies maximum size of the vector length in bytes while using SVE on Arm64", CLRConfig::LookupOptions::ParseIntegerAsBase10)
+#endif //defined(TARGET_LINUX) && (defined(DEBUG) || defined(_DEBUG))
 #endif
 
 ///

src/coreclr/vm/codeman.cpp

@@ -4,7 +4,10 @@
 //
 // codeman.cpp - a managment class for handling multiple code managers
 //
-
+#if defined(TARGET_LINUX) && (defined(DEBUG) || defined(_DEBUG))
+#include <sys/prctl.h>
+#include <sys/syscall.h>
+#endif // defined(TARGET_LINUX) && (defined(DEBUG) || defined(_DEBUG))
 #include "common.h"
 #include "jitinterface.h"
 #include "corjit.h"
@@ -1525,6 +1528,18 @@ void EEJitManager::SetCpuInfo()
 
     if (((cpuFeatures & ARM64IntrinsicConstants_Sve) != 0) && CLRConfig::GetConfigValue(CLRConfig::EXTERNAL_EnableArm64Sve))
     {
+#if defined(TARGET_LINUX) && (defined(DEBUG) || defined(_DEBUG))
+        int maxVectorLength = CLRConfig::GetConfigValue(CLRConfig::EXTERNAL_MaxVectorLength);
+
+        // Limit the SVE vector length to 'maxVectorLength' if the underlying hardware offers longer vectors.
+        if ((prctl(PR_SVE_GET_VL, 0,0,0,0) & PR_SVE_VL_LEN_MASK) > maxVectorLength)
+        {
+            if (prctl(PR_SVE_SET_VL, (maxVectorLength | PR_SVE_VL_INHERIT), 0, 0, 0) == -1)
+            {
+                LogErrorToHost("LoadAndInitializeJIT: prctl() FAILED - unable to set maxVectorLength to %d", maxVectorLength);
+            }
+        }
+#endif // defined(TARGET_LINUX) && (defined(DEBUG) || defined(_DEBUG))
         CPUCompileFlags.Set(InstructionSet_Sve);
     }