src/cpu-features.h

// Copyright 2018, VIXL authors
// All rights reserved.
//
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// modification, are permitted provided that the following conditions are met:
//
//   * Redistributions of source code must retain the above copyright notice,
//     this list of conditions and the following disclaimer.
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#ifndef VIXL_CPU_FEATURES_H
#define VIXL_CPU_FEATURES_H

#include <bitset>
#include <ostream>

#include "globals-vixl.h"

namespace vixl {


// VIXL aims to handle and detect all architectural features that are likely to
// influence code-generation decisions at EL0 (user-space).
//
// - There may be multiple VIXL feature flags for a given architectural
//   extension. This occurs where the extension allow components to be
//   implemented independently, or where kernel support is needed, and is likely
//   to be fragmented.
//
//   For example, Pointer Authentication (kPAuth*) has a separate feature flag
//   for access to PACGA, and to indicate that the QARMA algorithm is
//   implemented.
//
// - Conversely, some extensions have configuration options that do not affect
//   EL0, so these are presented as a single VIXL feature.
//
//   For example, the RAS extension (kRAS) has several variants, but the only
//   feature relevant to VIXL is the addition of the ESB instruction so we only
//   need a single flag.
//
// - VIXL offers separate flags for separate features even if they're
//   architecturally linked.
//
//   For example, the architecture requires kFPHalf and kNEONHalf to be equal,
//   but they have separate hardware ID register fields so VIXL presents them as
//   separate features.
//
// - VIXL can detect every feature for which it can generate code.
//
// - VIXL can detect some features for which it cannot generate code.
//
// The CPUFeatures::Feature enum — derived from the macro list below — is
// frequently extended. New features may be added to the list at any point, and
// no assumptions should be made about the numerical values assigned to each
// enum constant. The symbolic names can be considered to be stable.
//
// The debug descriptions are used only for debug output. The 'cpuinfo' strings
// are informative; VIXL does not use /proc/cpuinfo for feature detection.

// clang-format off
#define VIXL_CPU_FEATURE_LIST(V)                                               \
  /* If set, the OS traps and emulates MRS accesses to relevant (EL1) ID_*  */ \
  /* registers, so that the detailed feature registers can be read          */ \
  /* directly.                                                              */ \
                                                                               \
  /* Constant name        Debug description         Linux 'cpuinfo' string. */ \
  V(kIDRegisterEmulation, "ID register emulation",  "cpuid")                   \
                                                                               \
  V(kFP,                  "FP",                     "fp")                      \
  V(kNEON,                "NEON",                   "asimd")                   \
  V(kCRC32,               "CRC32",                  "crc32")                   \
  V(kDGH,                 "DGH",                    "dgh")                     \
  /* Speculation control features.                                          */ \
  V(kCSV2,                "CSV2",                   NULL)                      \
  V(kSCXTNUM,             "SCXTNUM",                NULL)                      \
  V(kCSV3,                "CSV3",                   NULL)                      \
  V(kSB,                  "SB",                     "sb")                      \
  V(kSPECRES,             "SPECRES",                NULL)                      \
  V(kSSBS,                "SSBS",                   NULL)                      \
  V(kSSBSControl,         "SSBS (PSTATE control)",  "ssbs")                    \
  /* Cryptographic support instructions.                                    */ \
  V(kAES,                 "AES",                    "aes")                     \
  V(kSHA1,                "SHA1",                   "sha1")                    \
  V(kSHA2,                "SHA2",                   "sha2")                    \
  /* A form of PMULL{2} with a 128-bit (1Q) result.                         */ \
  V(kPmull1Q,             "Pmull1Q",                "pmull")                   \
  /* Atomic operations on memory: CAS, LDADD, STADD, SWP, etc.              */ \
  V(kAtomics,             "Atomics",                "atomics")                 \
  /* Limited ordering regions: LDLAR, STLLR and their variants.             */ \
  V(kLORegions,           "LORegions",              NULL)                      \
  /* Rounding doubling multiply add/subtract: SQRDMLAH and SQRDMLSH.        */ \
  V(kRDM,                 "RDM",                    "asimdrdm")                \
  /* Scalable Vector Extension.                                             */ \
  V(kSVE,                 "SVE",                    "sve")                     \
  V(kSVEF64MM,            "SVE F64MM",              "svef64mm")                \
  V(kSVEF32MM,            "SVE F32MM",              "svef32mm")                \
  V(kSVEI8MM,             "SVE I8MM",               "svei8imm")                \
  V(kSVEBF16,             "SVE BFloat16",           "svebf16")                 \
  /* SDOT and UDOT support (in NEON).                                       */ \
  V(kDotProduct,          "DotProduct",             "asimddp")                 \
  /* Int8 matrix multiplication (in NEON).                                  */ \
  V(kI8MM,                "NEON I8MM",              "i8mm")                    \
  /* Half-precision (FP16) support for FP and NEON, respectively.           */ \
  V(kFPHalf,              "FPHalf",                 "fphp")                    \
  V(kNEONHalf,            "NEONHalf",               "asimdhp")                 \
  /* BFloat16 support (in both FP and NEON.)                                */ \
  V(kBF16,                "FP/NEON BFloat 16",      "bf16")                    \
  /* The RAS extension, including the ESB instruction.                      */ \
  V(kRAS,                 "RAS",                    NULL)                      \
  /* Data cache clean to the point of persistence: DC CVAP.                 */ \
  V(kDCPoP,               "DCPoP",                  "dcpop")                   \
  /* Data cache clean to the point of deep persistence: DC CVADP.           */ \
  V(kDCCVADP,             "DCCVADP",                "dcpodp")                  \
  /* Cryptographic support instructions.                                    */ \
  V(kSHA3,                "SHA3",                   "sha3")                    \
  V(kSHA512,              "SHA512",                 "sha512")                  \
  V(kSM3,                 "SM3",                    "sm3")                     \
  V(kSM4,                 "SM4",                    "sm4")                     \
  /* Pointer authentication for addresses.                                  */ \
  V(kPAuth,               "PAuth",                  "paca")                    \
  /* Pointer authentication for addresses uses QARMA.                       */ \
  V(kPAuthQARMA,          "PAuthQARMA",             NULL)                      \
  /* Generic authentication (using the PACGA instruction).                  */ \
  V(kPAuthGeneric,        "PAuthGeneric",           "pacg")                    \
  /* Generic authentication uses QARMA.                                     */ \
  V(kPAuthGenericQARMA,   "PAuthGenericQARMA",      NULL)                      \
  /* JavaScript-style FP -> integer conversion instruction: FJCVTZS.        */ \
  V(kJSCVT,               "JSCVT",                  "jscvt")                   \
  /* Complex number support for NEON: FCMLA and FCADD.                      */ \
  V(kFcma,                "Fcma",                   "fcma")                    \
  /* RCpc-based model (for weaker release consistency): LDAPR and variants. */ \
  V(kRCpc,                "RCpc",                   "lrcpc")                   \
  V(kRCpcImm,             "RCpc (imm)",             "ilrcpc")                  \
  /* Flag manipulation instructions: SETF{8,16}, CFINV, RMIF.               */ \
  V(kFlagM,               "FlagM",                  "flagm")                   \
  /* Unaligned single-copy atomicity.                                       */ \
  V(kUSCAT,               "USCAT",                  "uscat")                   \
  /* FP16 fused multiply-add or -subtract long: FMLAL{2}, FMLSL{2}.         */ \
  V(kFHM,                 "FHM",                    "asimdfhm")                \
  /* Data-independent timing (for selected instructions).                   */ \
  V(kDIT,                 "DIT",                    "dit")                     \
  /* Branch target identification.                                          */ \
  V(kBTI,                 "BTI",                    "bti")                     \
  /* Flag manipulation instructions: {AX,XA}FLAG                            */ \
  V(kAXFlag,              "AXFlag",                 "flagm2")                  \
  /* Random number generation extension,                                    */ \
  V(kRNG,                 "RNG",                    "rng")                     \
  /* Floating-point round to {32,64}-bit integer.                           */ \
  V(kFrintToFixedSizedInt,"Frint (bounded)",        "frint")                   \
  /* Memory Tagging Extension.                                              */ \
  V(kMTEInstructions,     "MTE (EL0 instructions)", NULL)                      \
  V(kMTE,                 "MTE",                    NULL)                      \
  /* PAuth extensions.                                                      */ \
  V(kPAuthEnhancedPAC,    "PAuth EnhancedPAC",      NULL)                      \
  V(kPAuthEnhancedPAC2,   "PAuth EnhancedPAC2",     NULL)                      \
  V(kPAuthFPAC,           "PAuth FPAC",             NULL)                      \
  V(kPAuthFPACCombined,   "PAuth FPACCombined",     NULL)                      \
  /* Scalable Vector Extension 2.                                           */ \
  V(kSVE2,                "SVE2",                   "sve2")                    \
  V(kSVESM4,              "SVE SM4",                "svesm4")                  \
  V(kSVESHA3,             "SVE SHA3",               "svesha3")                 \
  V(kSVEBitPerm,          "SVE BitPerm",            "svebitperm")              \
  V(kSVEAES,              "SVE AES",                "sveaes")                  \
  V(kSVEPmull128,         "SVE Pmull128",           "svepmull")                \
  /* Alternate floating-point behavior                                      */ \
  V(kAFP,                 "AFP",                    "afp")                     \
  /* Enhanced Counter Virtualization                                        */ \
  V(kECV,                 "ECV",                    "ecv")                     \
  /* Increased precision of Reciprocal Estimate and Square Root Estimate    */ \
  V(kRPRES,               "RPRES",                  "rpres")
// clang-format on


class CPUFeaturesConstIterator;

// A representation of the set of features known to be supported by the target
// device. Each feature is represented by a simple boolean flag.
//
//   - When the Assembler is asked to assemble an instruction, it asserts (in
//     debug mode) that the necessary features are available.
//
//   - TODO: The MacroAssembler relies on the Assembler's assertions, but in
//     some cases it may be useful for macros to generate a fall-back sequence
//     in case features are not available.
//
//   - The Simulator assumes by default that all features are available, but it
//     is possible to configure it to fail if the simulated code uses features
//     that are not enabled.
//
//     The Simulator also offers pseudo-instructions to allow features to be
//     enabled and disabled dynamically. This is useful when you want to ensure
//     that some features are constrained to certain areas of code.
//
//   - The base Disassembler knows nothing about CPU features, but the
//     PrintDisassembler can be configured to annotate its output with warnings
//     about unavailable features. The Simulator uses this feature when
//     instruction trace is enabled.
//
//   - The Decoder-based components -- the Simulator and PrintDisassembler --
//     rely on a CPUFeaturesAuditor visitor. This visitor keeps a list of
//     features actually encountered so that a large block of code can be
//     examined (either directly or through simulation), and the required
//     features analysed later.
//
// Expected usage:
//
//     // By default, VIXL uses CPUFeatures::AArch64LegacyBaseline(), for
//     // compatibility with older version of VIXL.
//     MacroAssembler masm;
//
//     // Generate code only for the current CPU.
//     masm.SetCPUFeatures(CPUFeatures::InferFromOS());
//
//     // Turn off feature checking entirely.
//     masm.SetCPUFeatures(CPUFeatures::All());
//
// Feature set manipulation:
//
//     CPUFeatures f;  // The default constructor gives an empty set.
//     // Individual features can be added (or removed).
//     f.Combine(CPUFeatures::kFP, CPUFeatures::kNEON, CPUFeatures::AES);
//     f.Remove(CPUFeatures::kNEON);
//
//     // Some helpers exist for extensions that provide several features.
//     f.Remove(CPUFeatures::All());
//     f.Combine(CPUFeatures::AArch64LegacyBaseline());
//
//     // Chained construction is also possible.
//     CPUFeatures g =
//         f.With(CPUFeatures::kPmull1Q).Without(CPUFeatures::kCRC32);
//
//     // Features can be queried. Where multiple features are given, they are
//     // combined with logical AND.
//     if (h.Has(CPUFeatures::kNEON)) { ... }
//     if (h.Has(CPUFeatures::kFP, CPUFeatures::kNEON)) { ... }
//     if (h.Has(g)) { ... }
//     // If the empty set is requested, the result is always 'true'.
//     VIXL_ASSERT(h.Has(CPUFeatures()));
//
//     // For debug and reporting purposes, features can be enumerated (or
//     // printed directly):
//     std::cout << CPUFeatures::kNEON;  // Prints something like "NEON".
//     std::cout << f;  // Prints something like "FP, NEON, CRC32".
class CPUFeatures {
 public:
  // clang-format off
  // Individual features.
  // These should be treated as opaque tokens. User code should not rely on
  // specific numeric values or ordering.
  enum Feature {
    // Refer to VIXL_CPU_FEATURE_LIST (above) for the list of feature names that
    // this class supports.

    kNone = -1,
#define VIXL_DECLARE_FEATURE(SYMBOL, NAME, CPUINFO) SYMBOL,
    VIXL_CPU_FEATURE_LIST(VIXL_DECLARE_FEATURE)
#undef VIXL_DECLARE_FEATURE
    kNumberOfFeatures
  };
  // clang-format on

  // By default, construct with no features enabled.
  CPUFeatures() : features_{} {}

  // Construct with some features already enabled.
  template <typename T, typename... U>
  CPUFeatures(T first, U... others) : features_{} {
    Combine(first, others...);
  }

  // Construct with all features enabled. This can be used to disable feature
  // checking: `Has(...)` returns true regardless of the argument.
  static CPUFeatures All();

  // Construct an empty CPUFeatures. This is equivalent to the default
  // constructor, but is provided for symmetry and convenience.
  static CPUFeatures None() { return CPUFeatures(); }

  // The presence of these features was assumed by version of VIXL before this
  // API was added, so using this set by default ensures API compatibility.
  static CPUFeatures AArch64LegacyBaseline() {
    return CPUFeatures(kFP, kNEON, kCRC32);
  }

  // Construct a new CPUFeatures object using ID registers. This assumes that
  // kIDRegisterEmulation is present.
  static CPUFeatures InferFromIDRegisters();

  enum QueryIDRegistersOption {
    kDontQueryIDRegisters,
    kQueryIDRegistersIfAvailable
  };

  // Construct a new CPUFeatures object based on what the OS reports.
  static CPUFeatures InferFromOS(
      QueryIDRegistersOption option = kQueryIDRegistersIfAvailable);

  // Combine another CPUFeatures object into this one. Features that already
  // exist in this set are left unchanged.
  void Combine(const CPUFeatures& other);

  // Combine a specific feature into this set. If it already exists in the set,
  // the set is left unchanged.
  void Combine(Feature feature);

  // Combine multiple features (or feature sets) into this set.
  template <typename T, typename... U>
  void Combine(T first, U... others) {
    Combine(first);
    Combine(others...);
  }

  // Remove features in another CPUFeatures object from this one.
  void Remove(const CPUFeatures& other);

  // Remove a specific feature from this set. This has no effect if the feature
  // doesn't exist in the set.
  void Remove(Feature feature0);

  // Remove multiple features (or feature sets) from this set.
  template <typename T, typename... U>
  void Remove(T first, U... others) {
    Remove(first);
    Remove(others...);
  }

  // Chaining helpers for convenient construction by combining other CPUFeatures
  // or individual Features.
  template <typename... T>
  CPUFeatures With(T... others) const {
    CPUFeatures f(*this);
    f.Combine(others...);
    return f;
  }

  template <typename... T>
  CPUFeatures Without(T... others) const {
    CPUFeatures f(*this);
    f.Remove(others...);
    return f;
  }

  // Test whether the `other` feature set is equal to or a subset of this one.
  bool Has(const CPUFeatures& other) const;

  // Test whether a single feature exists in this set.
  // Note that `Has(kNone)` always returns true.
  bool Has(Feature feature) const;

  // Test whether all of the specified features exist in this set.
  template <typename T, typename... U>
  bool Has(T first, U... others) const {
    return Has(first) && Has(others...);
  }

  // Return the number of enabled features.
  size_t Count() const;
  bool HasNoFeatures() const { return Count() == 0; }

  // Check for equivalence.
  bool operator==(const CPUFeatures& other) const {
    return Has(other) && other.Has(*this);
  }
  bool operator!=(const CPUFeatures& other) const { return !(*this == other); }

  typedef CPUFeaturesConstIterator const_iterator;

  const_iterator begin() const;
  const_iterator end() const;

 private:
  // Each bit represents a feature. This set will be extended as needed.
  std::bitset<kNumberOfFeatures> features_;

  friend std::ostream& operator<<(std::ostream& os,
                                  const vixl::CPUFeatures& features);
};

std::ostream& operator<<(std::ostream& os, vixl::CPUFeatures::Feature feature);
std::ostream& operator<<(std::ostream& os, const vixl::CPUFeatures& features);

// This is not a proper C++ iterator type, but it simulates enough of
// ForwardIterator that simple loops can be written.
class CPUFeaturesConstIterator {
 public:
  CPUFeaturesConstIterator(const CPUFeatures* cpu_features = NULL,
                           CPUFeatures::Feature start = CPUFeatures::kNone)
      : cpu_features_(cpu_features), feature_(start) {
    VIXL_ASSERT(IsValid());
  }

  bool operator==(const CPUFeaturesConstIterator& other) const;
  bool operator!=(const CPUFeaturesConstIterator& other) const {
    return !(*this == other);
  }
  CPUFeaturesConstIterator& operator++();
  CPUFeaturesConstIterator operator++(int);

  CPUFeatures::Feature operator*() const {
    VIXL_ASSERT(IsValid());
    return feature_;
  }

  // For proper support of C++'s simplest "Iterator" concept, this class would
  // have to define member types (such as CPUFeaturesIterator::pointer) to make
  // it appear as if it iterates over Feature objects in memory. That is, we'd
  // need CPUFeatures::iterator to behave like std::vector<Feature>::iterator.
  // This is at least partially possible -- the std::vector<bool> specialisation
  // does something similar -- but it doesn't seem worthwhile for a
  // special-purpose debug helper, so they are omitted here.
 private:
  const CPUFeatures* cpu_features_;
  CPUFeatures::Feature feature_;

  bool IsValid() const {
    if (cpu_features_ == NULL) {
      return feature_ == CPUFeatures::kNone;
    }
    return cpu_features_->Has(feature_);
  }
};

// A convenience scope for temporarily modifying a CPU features object. This
// allows features to be enabled for short sequences.
//
// Expected usage:
//
//  {
//    CPUFeaturesScope cpu(&masm, CPUFeatures::kCRC32);
//    // This scope can now use CRC32, as well as anything else that was enabled
//    // before the scope.
//
//    ...
//
//    // At the end of the scope, the original CPU features are restored.
//  }
class CPUFeaturesScope {
 public:
  // Start a CPUFeaturesScope on any object that implements
  // `CPUFeatures* GetCPUFeatures()`.
  template <typename T>
  explicit CPUFeaturesScope(T* cpu_features_wrapper)
      : cpu_features_(cpu_features_wrapper->GetCPUFeatures()),
        old_features_(*cpu_features_) {}

  // Start a CPUFeaturesScope on any object that implements
  // `CPUFeatures* GetCPUFeatures()`, with the specified features enabled.
  template <typename T, typename U, typename... V>
  CPUFeaturesScope(T* cpu_features_wrapper, U first, V... features)
      : cpu_features_(cpu_features_wrapper->GetCPUFeatures()),
        old_features_(*cpu_features_) {
    cpu_features_->Combine(first, features...);
  }

  ~CPUFeaturesScope() { *cpu_features_ = old_features_; }

  // For advanced usage, the CPUFeatures object can be accessed directly.
  // The scope will restore the original state when it ends.

  CPUFeatures* GetCPUFeatures() const { return cpu_features_; }

  void SetCPUFeatures(const CPUFeatures& cpu_features) {
    *cpu_features_ = cpu_features;
  }

 private:
  CPUFeatures* const cpu_features_;
  const CPUFeatures old_features_;
};


}  // namespace vixl

#endif  // VIXL_CPU_FEATURES_H