[lldb][AArch64] Add SME streaming vector length pseduo register

[DavidSpickett]

Summary

This adds a register "svg" which mirrors SVE's "vg" register.
This reports the streaming vector length at all times, read
from the ZA ptrace header.

This register is needed first to implement ZA resizing as
the streaming vector length changes. Like vg, svg will be
expedited to the client so it can reconfigure its register
definitions.

The other use is for users to be able to know the streaming
vector length without resorting to counting the (many, many)
bytes in ZA, or temporarily entering streaming mode (which
would be destructive).

Some refactoring has been done so we don't have to recalculate the
register offsets twice.

Testing for this will come in a later patch.

[DavidSpickett]

Rebase

[omjavaid]

Why do we have svg and za in different register sets?

[DavidSpickett]

Made sense at the time with it being it's own regset in ptrace. Current state is:

Scalable Matrix Array Storage Registers:
        za = {<...>}

Scalable Matrix Extension Registers:
       svg = 0x0000000000000004
      svcr = 0x0000000000000003

But I agree, ZA could go in the latter group as you won't have ZA without SME.

I'll give it a go.

[DavidSpickett]

Adjust now that ZA is in the SME set. Putting SVG first for readability and
ease of resizing ZA later.

[DavidSpickett]

Why do we have svg and za in different register sets?

Done.

[DavidSpickett]

Scalable Matrix Extension Registers:
      svcr = 0x0000000000000000
       svg = 0x0000000000000004
        za = {0x00 <...>}

Is the layout now.

[DavidSpickett]

Rebase

[omjavaid]

This looks fine just couple of nits inline.

lldb/source/Plugins/Process/Linux/NativeRegisterContextLinux_arm64.cpp

354

this block of code requires clang-format run

lldb/source/Plugins/Process/Linux/NativeRegisterContextLinux_arm64.h

117

should we name this to sme_pseudo_regs ? sme_regs suggests struct could include ZA as well.

[DavidSpickett]

• sme_regs -> sme_pseudo_regs, also changed the accesor method names.
• clang-format

[DavidSpickett]

Will apply the rename in core files as well later.

[DavidSpickett]

Note that GetSMEOffset refers to the whole register set which does include ZA, so no change of name there.

[DavidSpickett]

Rebase

[omjavaid]

This is LGTM as you suggested pending child reviews.

[DavidSpickett]

Rebase

lldb/source/Plugins/Process/Linux/NativeRegisterContextLinux_arm64.h

struct user_pac_mask {
     uint64_t data_mask;
     uint64_t insn_mask;
   };
 
   struct user_pac_mask m_pac_mask;
 
   uint64_t m_mte_ctrl_reg;
 
+  struct sme_pseudo_regs {
+    uint64_t svg_reg;
+  };
+
+  struct sme_pseudo_regs m_sme_pseudo_regs;
+
   struct tls_regs {
     uint64_t tpidr_reg;
     // Only valid when SME is present.
     uint64_t tpidr2_reg;
   };
 
   struct tls_regs m_tls_regs;
 
private:
   Status ReadMTEControl();
 
   Status WriteMTEControl();
 
   Status ReadTLS();
 
   Status WriteTLS();
 
+  Status ReadSMESVG();
+
   Status ReadZAHeader();
 
   Status ReadZA();
 
   Status WriteZA();
 
   // No WriteZAHeader because writing only the header will disable ZA.
   // Instead use WriteZA and ensure you have the correct ZA buffer size set
private:
   size_t GetZAHeaderSize() { return sizeof(m_za_header); }
 
   void *GetPACMask() { return &m_pac_mask; }
 
   void *GetMTEControl() { return &m_mte_ctrl_reg; }
 
   void *GetTLSBuffer() { return &m_tls_regs; }
 
+  void *GetSMEPseudoBuffer() { return &m_sme_pseudo_regs; }
+
   void *GetSVEBuffer() { return m_sve_ptrace_payload.data(); }
 
   size_t GetSVEHeaderSize() { return sizeof(m_sve_header); }
 
   size_t GetPACMaskSize() { return sizeof(m_pac_mask); }
 
   size_t GetSVEBufferSize() { return m_sve_ptrace_payload.size(); }
 
   unsigned GetSVERegSet();
 
   void *GetZABuffer() { return m_za_ptrace_payload.data(); };
 
   size_t GetZABufferSize() { return m_za_ptrace_payload.size(); }
 
   size_t GetMTEControlSize() { return sizeof(m_mte_ctrl_reg); }
 
   size_t GetTLSBufferSize() { return m_tls_size; }
 
+  size_t GetSMEPseudoBufferSize() { return sizeof(m_sme_pseudo_regs); }
+
   llvm::Error ReadHardwareDebugInfo() override;
 
   llvm::Error WriteHardwareDebugRegs(DREGType hwbType) override;
 
   uint32_t CalculateFprOffset(const RegisterInfo *reg_info) const;
 
   RegisterInfoPOSIX_arm64 &GetRegisterInfo() const;
 

lldb/source/Plugins/Process/Linux/NativeRegisterContextLinux_arm64.cpp

: NativeRegisterContextRegisterInfo(native_thread,
       NativeRegisterContextLinux(native_thread) {
   ::memset(&m_fpr, 0, sizeof(m_fpr));
   ::memset(&m_gpr_arm64, 0, sizeof(m_gpr_arm64));
   ::memset(&m_hwp_regs, 0, sizeof(m_hwp_regs));
   ::memset(&m_hbp_regs, 0, sizeof(m_hbp_regs));
   ::memset(&m_sve_header, 0, sizeof(m_sve_header));
   ::memset(&m_pac_mask, 0, sizeof(m_pac_mask));
   ::memset(&m_tls_regs, 0, sizeof(m_tls_regs));
+  ::memset(&m_sme_pseudo_regs, 0, sizeof(m_sme_pseudo_regs));
 
   m_mte_ctrl_reg = 0;
 
   // 16 is just a maximum value, query hardware for actual watchpoint count
   m_max_hwp_supported = 16;
   m_max_hbp_supported = 16;
 
   m_refresh_hwdebug_info = true;
if (IsGPR(reg)) {
     error = ReadMTEControl();
     if (error.Fail())
       return error;
 
     offset = reg_info->byte_offset - GetRegisterInfo().GetMTEOffset();
     assert(offset < GetMTEControlSize());
     src = (uint8_t *)GetMTEControl() + offset;
   } else if (IsSME(reg)) {
+    if (GetRegisterInfo().IsSMERegZA(reg)) {
       error = ReadZAHeader();
       if (error.Fail())
         return error;
 
       // If there is only a header and no registers, ZA is inactive. Read as 0
       // in this case.
       if (m_za_header.size == sizeof(m_za_header)) {
         // This will get reconfigured/reset later, so we are safe to use it.
         // ZA is a square of VL * VL and the ptrace buffer also includes the
         // header itself.
         m_za_ptrace_payload.resize(((m_za_header.vl) * (m_za_header.vl)) +
                                    GetZAHeaderSize());
         std::fill(m_za_ptrace_payload.begin(), m_za_ptrace_payload.end(), 0);
       } else {
         // ZA is active, read the real register.
         error = ReadZA();
         if (error.Fail())
           return error;
       }
 
-    // ZA is part of the SME set but uses a seperate member buffer for storage.
-    // Therefore its effective byte offset is always 0 even if it isn't 0 within
-    // the SME register set.
+      // ZA is part of the SME set but uses a seperate member buffer for
+      // storage. Therefore its effective byte offset is always 0 even if it
+      // isn't 0 within the SME register set.
       src = (uint8_t *)GetZABuffer() + GetZAHeaderSize();
+    } else {
+      error = ReadSMESVG();
+      if (error.Fail())
+        return error;
+
+      offset = reg_info->byte_offset - GetRegisterInfo().GetSMEOffset();
+      assert(offset < GetSMEPseudoBufferSize());
+      src = (uint8_t *)GetSMEPseudoBuffer() + offset;
+    }
   } else
     return Status("failed - register wasn't recognized to be a GPR or an FPR, "
                   "write strategy unknown");
 
   reg_value.SetFromMemoryData(*reg_info, src, reg_info->byte_size,
                               eByteOrderLittle, error);
 
   return error;
if (IsGPR(reg)) {
 
     offset = reg_info->byte_offset - GetRegisterInfo().GetTLSOffset();
     assert(offset < GetTLSBufferSize());
     dst = (uint8_t *)GetTLSBuffer() + offset;
     ::memcpy(dst, reg_value.GetBytes(), reg_info->byte_size);
 
     return WriteTLS();
   } else if (IsSME(reg)) {
+    if (!GetRegisterInfo().IsSMERegZA(reg))
+      return Status("Writing to SVG is not supported.");
+
     error = ReadZA();
     if (error.Fail())
       return error;
 
     // ZA is part of the SME set but not stored with the other SME registers.
     // So its byte offset is effectively always 0.
     dst = (uint8_t *)GetZABuffer() + GetZAHeaderSize();
     ::memcpy(dst, reg_value.GetBytes(), reg_info->byte_size);
// Between non-streaming and streaming mode, the layout is identical.
              m_sve_state == SVEState::Streaming) {
     uint32_t sve_z0_offset = GetGPRSize() + 16;
     sve_reg_offset =
         sve::SigRegsOffset() + reg_info->byte_offset - sve_z0_offset;
   }
   return sve_reg_offset;
 }
 
+Status NativeRegisterContextLinux_arm64::ReadSMESVG() {
+  // This register is the streaming vector length, so we will get it from
+  // NT_ARM_ZA regardless of the current streaming mode.
+  Status error = ReadZAHeader();
+  if (error.Success())
+    m_sme_pseudo_regs.svg_reg = m_za_header.vl / 8;
+
+  return error;
+}
+
 std::vector<uint32_t> NativeRegisterContextLinux_arm64::GetExpeditedRegisters(
     ExpeditedRegs expType) const {
   std::vector<uint32_t> expedited_reg_nums =
       NativeRegisterContext::GetExpeditedRegisters(expType);
   // SVE, non-streaming vector length.
   if (m_sve_state == SVEState::FPSIMD || m_sve_state == SVEState::Full)
     expedited_reg_nums.push_back(GetRegisterInfo().GetRegNumSVEVG());
+  // SME, streaming vector length. This is used by the ZA register which is
+  // present even when streaming mode is not enabled.
+  if (GetRegisterInfo().IsSSVEEnabled())
+    expedited_reg_nums.push_back(GetRegisterInfo().GetRegNumSMESVG());
 
   return expedited_reg_nums;
 }
 
 llvm::Expected<NativeRegisterContextLinux::MemoryTaggingDetails>
 NativeRegisterContextLinux_arm64::GetMemoryTaggingDetails(int32_t type) {
   if (type == MemoryTagManagerAArch64MTE::eMTE_allocation) {
     return MemoryTaggingDetails{std::make_unique<MemoryTagManagerAArch64MTE>(),

lldb/source/Plugins/Process/Utility/RegisterInfoPOSIX_arm64.h

public:
   bool IsSVEReg(unsigned reg) const;
   bool IsSVEZReg(unsigned reg) const;
   bool IsSVEPReg(unsigned reg) const;
   bool IsSVERegVG(unsigned reg) const;
   bool IsPAuthReg(unsigned reg) const;
   bool IsMTEReg(unsigned reg) const;
   bool IsTLSReg(unsigned reg) const;
   bool IsSMEReg(unsigned reg) const;
+  bool IsSMERegZA(unsigned reg) const;
 
   uint32_t GetRegNumSVEZ0() const;
   uint32_t GetRegNumSVEFFR() const;
   uint32_t GetRegNumFPCR() const;
   uint32_t GetRegNumFPSR() const;
   uint32_t GetRegNumSVEVG() const;
+  uint32_t GetRegNumSMESVG() const;
   uint32_t GetPAuthOffset() const;
   uint32_t GetMTEOffset() const;
   uint32_t GetTLSOffset() const;
   uint32_t GetSMEOffset() const;
 
 private:
   typedef std::map<uint32_t, std::vector<lldb_private::RegisterInfo>>
       per_vq_register_infos;

lldb/source/Plugins/Process/Utility/RegisterInfoPOSIX_arm64.cpp

 static lldb_private::RegisterInfo g_register_infos_mte[] = {
     DEFINE_EXTENSION_REG(mte_ctrl)};
 
 static lldb_private::RegisterInfo g_register_infos_tls[] = {
     DEFINE_EXTENSION_REG(tpidr),
     // Only present when SME is present
     DEFINE_EXTENSION_REG(tpidr2)};
 
-static lldb_private::RegisterInfo g_register_infos_sme[] =
+static lldb_private::RegisterInfo g_register_infos_sme[] = {
+    DEFINE_EXTENSION_REG(svg),
     // 16 is a default size we will change later.
-    {{"za", nullptr, 16, 0, lldb::eEncodingVector, lldb::eFormatVectorOfUInt8,
-      KIND_ALL_INVALID, nullptr, nullptr, nullptr}};
+    {"za", nullptr, 16, 0, lldb::eEncodingVector, lldb::eFormatVectorOfUInt8,
 
 // Number of register sets provided by this context.
 enum {
   k_num_gpr_registers = gpr_w28 - gpr_x0 + 1,
   k_num_fpr_registers = fpu_fpcr - fpu_v0 + 1,
   k_num_sve_registers = sve_ffr - sve_vg + 1,
   k_num_mte_register = 1,
   // Number of TLS registers is dynamic so it is not listed here.
   k_num_pauth_register = 2,
-  k_num_sme_register = 1,
+  k_num_sme_register = 2,
   k_num_register_sets_default = 2,
   k_num_register_sets = 3
 };
 
 // ARM64 general purpose registers.
 static const uint32_t g_gpr_regnums_arm64[] = {
     gpr_x0,  gpr_x1,   gpr_x2,  gpr_x3,
     gpr_x4,  gpr_x5,   gpr_x6,  gpr_x7,
if (!VectorSizeIsValid(za_vq) || m_za_reg_vq == za_vq)
     return;
 
   m_za_reg_vq = za_vq;
 
   // For SVE changes, we replace m_register_info_p completely. ZA is in a
   // dynamic set and is just 1 register so we make an exception to const here.
   lldb_private::RegisterInfo *non_const_reginfo =
       const_cast<lldb_private::RegisterInfo *>(m_register_info_p);
-  non_const_reginfo[m_sme_regnum_collection[0]].byte_size =
+  non_const_reginfo[m_sme_regnum_collection[1]].byte_size =
       (za_vq * 16) * (za_vq * 16);
 }
 
 bool RegisterInfoPOSIX_arm64::IsSVEReg(unsigned reg) const {
   if (m_vector_reg_vq > eVectorQuadwordAArch64)
     return (sve_vg <= reg && reg <= sve_ffr);
   else
     return false;
 }
 
 bool RegisterInfoPOSIX_arm64::IsSVEZReg(unsigned reg) const {
   return (sve_z0 <= reg && reg <= sve_z31);
 }
 
 bool RegisterInfoPOSIX_arm64::IsSVEPReg(unsigned reg) const {
   return (sve_p0 <= reg && reg <= sve_p15);
 }
 
 bool RegisterInfoPOSIX_arm64::IsSVERegVG(unsigned reg) const {
   return sve_vg == reg;
 }
 
+bool RegisterInfoPOSIX_arm64::IsSMERegZA(unsigned reg) const {
+  return reg == m_sme_regnum_collection[1];
+}
+
 bool RegisterInfoPOSIX_arm64::IsPAuthReg(unsigned reg) const {
   return llvm::is_contained(pauth_regnum_collection, reg);
 }
 
 bool RegisterInfoPOSIX_arm64::IsMTEReg(unsigned reg) const {
   return llvm::is_contained(m_mte_regnum_collection, reg);
 }
 

 uint32_t RegisterInfoPOSIX_arm64::GetRegNumSVEFFR() const { return sve_ffr; }
 
 uint32_t RegisterInfoPOSIX_arm64::GetRegNumFPCR() const { return fpu_fpcr; }
 
 uint32_t RegisterInfoPOSIX_arm64::GetRegNumFPSR() const { return fpu_fpsr; }
 
 uint32_t RegisterInfoPOSIX_arm64::GetRegNumSVEVG() const { return sve_vg; }
 
+uint32_t RegisterInfoPOSIX_arm64::GetRegNumSMESVG() const {
+  return m_sme_regnum_collection[0];
+}
+
 uint32_t RegisterInfoPOSIX_arm64::GetPAuthOffset() const {
   return m_register_info_p[pauth_regnum_collection[0]].byte_offset;
 }
 
 uint32_t RegisterInfoPOSIX_arm64::GetMTEOffset() const {
   return m_register_info_p[m_mte_regnum_collection[0]].byte_offset;
 }
 
 uint32_t RegisterInfoPOSIX_arm64::GetTLSOffset() const {
   return m_register_info_p[m_tls_regnum_collection[0]].byte_offset;
 }
 
 uint32_t RegisterInfoPOSIX_arm64::GetSMEOffset() const {
   return m_register_info_p[m_sme_regnum_collection[0]].byte_offset;
 }