[SystemZ][z/OS] Implement getHostCPUName for z/OS

- Currently, the host cpu information is not easily available on z/OS as in other platforms.
- This information is stored in the Communications Vector Table (https://www.ibm.com/docs/en/zos/2.2.0?topic=information-cvt-mapping)

Reviewed By: uweigand

Differential Revision: https://reviews.llvm.org/D102793

include/llvm/Support/BCD.h

@@ -0,0 +1,53 @@
+//===- llvm/Support/BCD.h - Binary-Coded Decimal utility functions -*- C++ -*-//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file declares some utility functions for encoding/decoding BCD values.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_SUPPORT_BCD_H
+#define LLVM_SUPPORT_BCD_H
+
+#include <assert.h>
+#include <cstddef>
+#include <cstdint>
+
+namespace llvm {
+
+// Decode a packed BCD value.
+// Maximum value of int64_t is 9,223,372,036,854,775,807. These are 18 usable
+// decimal digits. Thus BCD numbers of up to 9 bytes can be converted.
+// Please note that s390 supports BCD numbers up to a length of 16 bytes.
+inline int64_t decodePackedBCD(const uint8_t *Ptr, size_t ByteLen,
+                               bool IsSigned = true) {
+  assert(ByteLen >= 1 && ByteLen <= 9 && "Invalid BCD number");
+  int64_t Value = 0;
+  size_t RunLen = ByteLen - static_cast<unsigned>(IsSigned);
+  for (size_t I = 0; I < RunLen; ++I) {
+    uint8_t DecodedByteValue = ((Ptr[I] >> 4) & 0x0f) * 10 + (Ptr[I] & 0x0f);
+    Value = (Value * 100) + DecodedByteValue;
+  }
+  if (IsSigned) {
+    uint8_t DecodedByteValue = (Ptr[ByteLen - 1] >> 4) & 0x0f;
+    uint8_t Sign = Ptr[ByteLen - 1] & 0x0f;
+    Value = (Value * 10) + DecodedByteValue;
+    if (Sign == 0x0d || Sign == 0x0b)
+      Value *= -1;
+  }
+  return Value;
+}
+
+template <typename ResultT, typename ValT>
+inline ResultT decodePackedBCD(const ValT Val, bool IsSigned = true) {
+  return static_cast<ResultT>(decodePackedBCD(
+      reinterpret_cast<const uint8_t *>(&Val), sizeof(ValT), IsSigned));
+}
+
+} // namespace llvm
+
+#endif // LLVM_SUPPORT_BCD_H

lib/Support/Host.cpp

@@ -18,6 +18,7 @@
 #include "llvm/ADT/StringSwitch.h"
 #include "llvm/ADT/Triple.h"
 #include "llvm/Config/llvm-config.h"
+#include "llvm/Support/BCD.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/MemoryBuffer.h"
@@ -296,6 +297,22 @@ StringRef sys::detail::getHostCPUNameForARM(StringRef ProcCpuinfoContent) {
   return "generic";
 }
 
+namespace {
+StringRef getCPUNameFromS390Model(unsigned int Id, bool HaveVectorSupport) {
+  if (Id >= 8561 && HaveVectorSupport)
+    return "z15";
+  if (Id >= 3906 && HaveVectorSupport)
+    return "z14";
+  if (Id >= 2964 && HaveVectorSupport)
+    return "z13";
+  if (Id >= 2827)
+    return "zEC12";
+  if (Id >= 2817)
+    return "z196";
+  return "generic";
+}
+} // end anonymous namespace
+
 StringRef sys::detail::getHostCPUNameForS390x(StringRef ProcCpuinfoContent) {
   // STIDP is a privileged operation, so use /proc/cpuinfo instead.
 
@@ -331,18 +348,8 @@ StringRef sys::detail::getHostCPUNameForS390x(StringRef ProcCpuinfoContent) {
       if (Pos != StringRef::npos) {
         Pos += sizeof("machine = ") - 1;
         unsigned int Id;
-        if (!Lines[I].drop_front(Pos).getAsInteger(10, Id)) {
-          if (Id >= 8561 && HaveVectorSupport)
-            return "z15";
-          if (Id >= 3906 && HaveVectorSupport)
-            return "z14";
-          if (Id >= 2964 && HaveVectorSupport)
-            return "z13";
-          if (Id >= 2827)
-            return "zEC12";
-          if (Id >= 2817)
-            return "z196";
-        }
+        if (!Lines[I].drop_front(Pos).getAsInteger(10, Id))
+          return getCPUNameFromS390Model(Id, HaveVectorSupport);
       }
       break;
     }
@@ -1229,6 +1236,29 @@ StringRef sys::getHostCPUName() {
   StringRef Content = P ? P->getBuffer() : "";
   return detail::getHostCPUNameForS390x(Content);
 }
+#elif defined(__MVS__)
+StringRef sys::getHostCPUName() {
+  // Get pointer to Communications Vector Table (CVT).
+  // The pointer is located at offset 16 of the Prefixed Save Area (PSA).
+  // It is stored as 31 bit pointer and will be zero-extended to 64 bit.
+  int *StartToCVTOffset = reinterpret_cast<int *>(0x10);
+  // Since its stored as a 31-bit pointer, get the 4 bytes from the start
+  // of address.
+  int ReadValue = *StartToCVTOffset;
+  // Explicitly clear the high order bit.
+  ReadValue = (ReadValue & 0x7FFFFFFF);
+  char *CVT = reinterpret_cast<char *>(ReadValue);
+  // The model number is located in the CVT prefix at offset -6 and stored as
+  // signless packed decimal.
+  uint16_t Id = *(uint16_t *)&CVT[-6];
+  // Convert number to integer.
+  Id = decodePackedBCD<uint16_t>(Id, false);
+  // Check for vector support. It's stored in field CVTFLAG5 (offset 244),
+  // bit CVTVEF (X'80'). The facilities list is part of the PSA but the vector
+  // extension can only be used if bit CVTVEF is on.
+  bool HaveVectorSupport = CVT[244] & 0x80;
+  return getCPUNameFromS390Model(Id, HaveVectorSupport);
+}
 #elif defined(__APPLE__) && defined(__aarch64__)
 StringRef sys::getHostCPUName() {
   return "cyclone";

unittests/Support/Host.cpp

@@ -310,6 +310,54 @@ CPU revision    : 0
   EXPECT_EQ(sys::detail::getHostCPUNameForARM(Snapdragon865ProcCPUInfo), "cortex-a77");
 }
 
+TEST(getLinuxHostCPUName, s390x) {
+  SmallVector<std::string> ModelIDs(
+      {"8561", "3906", "2964", "2827", "2817", "7"});
+  SmallVector<std::string> VectorSupport({"", "vx"});
+  SmallVector<StringRef> ExpectedCPUs;
+
+  // Model Id: 8561
+  ExpectedCPUs.push_back("zEC12");
+  ExpectedCPUs.push_back("z15");
+
+  // Model Id: 3906
+  ExpectedCPUs.push_back("zEC12");
+  ExpectedCPUs.push_back("z14");
+
+  // Model Id: 2964
+  ExpectedCPUs.push_back("zEC12");
+  ExpectedCPUs.push_back("z13");
+
+  // Model Id: 2827
+  ExpectedCPUs.push_back("zEC12");
+  ExpectedCPUs.push_back("zEC12");
+
+  // Model Id: 2817
+  ExpectedCPUs.push_back("z196");
+  ExpectedCPUs.push_back("z196");
+
+  // Model Id: 7
+  ExpectedCPUs.push_back("generic");
+  ExpectedCPUs.push_back("generic");
+
+  const std::string DummyBaseVectorInfo =
+      "features : esan3 zarch stfle msa ldisp eimm dfp edat etf3eh highgprs "
+      "te ";
+  const std::string DummyBaseMachineInfo =
+      "processor 0: version = FF,  identification = 059C88,  machine = ";
+
+  int CheckIndex = 0;
+  for (size_t I = 0; I < ModelIDs.size(); I++) {
+    for (size_t J = 0; J < VectorSupport.size(); J++) {
+      const std::string DummyCPUInfo = DummyBaseVectorInfo + VectorSupport[J] +
+                                       "\n" + DummyBaseMachineInfo +
+                                       ModelIDs[I];
+      EXPECT_EQ(sys::detail::getHostCPUNameForS390x(DummyCPUInfo),
+                ExpectedCPUs[CheckIndex++]);
+    }
+  }
+}
+
 #if defined(__APPLE__) || defined(_AIX)
 static bool runAndGetCommandOutput(
     const char *ExePath, ArrayRef<llvm::StringRef> argv,