[Linux/x86] Fix writing of non-gpr registers on newer processors

[labath]

Summary

We're using ptrace(PTRACE_SETREGSET, NT_X86_XSTATE) to write all non-gpt
registers on x86 linux. Unfortunately, this method has a quirk, where
the kernel rejects all attempts to write to this area if one supplies a
buffer which is smaller than the area size (even though the kernel will
happily accept partial reads from it).

This means that if the CPU supports some new registers/extensions that
we don't know about (in my case it was the PKRU extension), we will fail
to write *any* non-gpr registers, even those that we know about.

Since this is a situation that's likely to appear again and again, I add
code to NativeRegisterContextLinux_x86_64 to detect the runtime size of
the area, and allocate an appropriate buffer. This does not mean that we
will start automatically supporting all new extensions, but it does mean
that the new extensions will not prevent the old ones from working.

This fixes tests attempting to write to non-gpr registers on new intel
processors (cca Kaby Lake Refresh).

[jankratochvil]

LGTM and it has fixed for me on Kaby Lake Refresh (i7-8650U):

lldb-Suite :: functionalities/register/register_command/TestRegisters.py
lldb-Suite :: tools/lldb-server/TestGdbRemoteRegisterState.py

[davezarzycki]

I've verified that this fixes my Skylake-SP (Xeon 8168) workstation. Thanks!

[davezarzycki]

Can we cherry-pick this into a release branch? Skylake (and newer) CPUs are far from rare these days, especially on cloud hosting providers.

[labath]

Thank you for the quick review.

In D59991#1448852, @davezarzycki wrote:

Can we cherry-pick this into a release branch? Skylake (and newer) CPUs are far from rare these days, especially on cloud hosting providers.

I think cherry-picking this would be a good idea (though I'd let it sit on the master branch for a bit of time first). However, I think the only release we can cherry-pick this to is 8.0.1, and that one is still a couple of months away (we've literally just wrapped 8.0). Nonetheless, I've filed a bug to do that https://bugs.llvm.org/show_bug.cgi?id=41330. If you're interested, you could also try to talk to the distro of your choice to see if they can roll out a quicker fix.

[JosephTremoulet]

lldb/trunk/source/Plugins/Process/Linux/NativeRegisterContextLinux_x86_64.cpp

282 ↗

(On Diff #193051)

This doesn't compile for me (on stock Ubuntu 16.04, so using gcc/libstdc++ 5.4.0), since my cpuid.h doesn't have __get_cpuid_count. Do I just need to update/fix my toolset, or is that a supported one that we should change this code to accommodate?

[labath]

gcc-5.4 technically supported, so we can try to make things work for you. I'd be best if you can create a patch that will make things work for you (since it's kinda hard for me to test that). Or at least, can you paste the contents of your cpuid.h somewhere?

[JosephTremoulet]

In D59991#1475694, @labath wrote:

gcc-5.4 technically supported, so we can try to make things work for you. I'd be best if you can create a patch that will make things work for you (since it's kinda hard for me to test that). Or at least, can you paste the contents of your cpuid.h somewhere?

Ok. I'd be happy to put a patch together... is there an existing pattern for this sort of thing that I should follow? E.g. define a helper llvm::get_cpuid_count function somewhere, similar to STLExtras? Or just define it in this file? Looking at the implementation of __get_cpuid_count in libc++, it's pretty short, my instinct would be to just inline that logic into the callsite here... LMK if there's a preferred approach.

[labath]

In D59991#1475709, @JosephTremoulet wrote:

In D59991#1475694, @labath wrote:

gcc-5.4 technically supported, so we can try to make things work for you. I'd be best if you can create a patch that will make things work for you (since it's kinda hard for me to test that). Or at least, can you paste the contents of your cpuid.h somewhere?

Ok. I'd be happy to put a patch together... is there an existing pattern for this sort of thing that I should follow? E.g. define a helper llvm::get_cpuid_count function somewhere, similar to STLExtras? Or just define it in this file? Looking at the implementation of __get_cpuid_count in libc++, it's pretty short, my instinct would be to just inline that logic into the callsite here... LMK if there's a preferred approach.

You can just put create a helper function at the top of this file. (This is assuming that we actually need to define a helper function, and that it's not possible to tweak this code slightly so that it works on all cpuid.h versions -- hard to say without looking at what your cpuid.h looks like.)

source/Plugins/Process/Linux/NativeRegisterContextLinux_x86_64.h

struct RegInfo {
     uint32_t first_mpxc;
     uint32_t last_mpxc;
     uint32_t first_dr;
     uint32_t gpr_flags;
   };
 
   // Private member variables.
   mutable XStateType m_xstate_type;
-  FPR m_fpr; // Extended States Area, named FPR for historical reasons.
+  std::unique_ptr<FPR, llvm::FreeDeleter>
+      m_xstate; // Extended States Area, named FPR for historical reasons.
   struct iovec m_iovec;
   YMM m_ymm_set;
   MPX m_mpx_set;
   RegInfo m_reg_info;
   uint64_t m_gpr_x86_64[k_num_gpr_registers_x86_64];
   uint32_t m_fctrl_offset_in_userarea;
 
   // Private member methods.

source/Plugins/Process/Linux/NativeRegisterContextLinux_x86_64.cpp

 #include "lldb/Host/HostInfo.h"
 #include "lldb/Utility/DataBufferHeap.h"
 #include "lldb/Utility/Log.h"
 #include "lldb/Utility/RegisterValue.h"
 #include "lldb/Utility/Status.h"
 
 #include "Plugins/Process/Utility/RegisterContextLinux_i386.h"
 #include "Plugins/Process/Utility/RegisterContextLinux_x86_64.h"
-
+#include <cpuid.h>
 #include <linux/elf.h>
 
 using namespace lldb_private;
 using namespace lldb_private::process_linux;
 
 // ----------------------------------------------------------------------------
 // Private namespace.
 // ----------------------------------------------------------------------------
if (HostInfo::GetArchitecture().GetAddressByteSize() == 4) {
     assert((HostInfo::GetArchitecture().GetAddressByteSize() == 8) &&
            "Register setting path assumes this is a 64-bit host");
     // X86_64 hosts know how to work with 64-bit and 32-bit EXEs using the
     // x86_64 register context.
     return new RegisterContextLinux_x86_64(target_arch);
   }
 }
 
+// Return the size of the XSTATE area supported on this cpu. It is necessary to
+// allocate the full size of the area even if we do not use/recognise all of it
+// because ptrace(PTRACE_SETREGSET, NT_X86_XSTATE) will refuse to write to it if
+// we do not pass it a buffer of sufficient size. The size is always at least
+// sizeof(FPR) so that the allocated buffer can be safely cast to FPR*.
+static std::size_t GetXSTATESize() {
+  unsigned int eax, ebx, ecx, edx;
+  // First check whether the XSTATE are is supported at all.
+  if (!__get_cpuid(1, &eax, &ebx, &ecx, &edx) || !(ecx & bit_XSAVE))
+    return sizeof(FPR);
+
+  // Then fetch the maximum size of the area.
+  if (!__get_cpuid_count(0x0d, 0, &eax, &ebx, &ecx, &edx))
+    return sizeof(FPR);
+  return std::max<std::size_t>(ecx, sizeof(FPR));
+}
+
 NativeRegisterContextLinux_x86_64::NativeRegisterContextLinux_x86_64(
     const ArchSpec &target_arch, NativeThreadProtocol &native_thread)
     : NativeRegisterContextLinux(native_thread,
                                  CreateRegisterInfoInterface(target_arch)),
-      m_xstate_type(XStateType::Invalid), m_fpr(), m_iovec(), m_ymm_set(),
-      m_mpx_set(), m_reg_info(), m_gpr_x86_64() {
+      m_xstate_type(XStateType::Invalid), m_ymm_set(), m_mpx_set(),
+      m_reg_info(), m_gpr_x86_64() {
   // Set up data about ranges of valid registers.
   switch (target_arch.GetMachine()) {
   case llvm::Triple::x86:
     m_reg_info.num_registers = k_num_registers_i386;
     m_reg_info.num_gpr_registers = k_num_gpr_registers_i386;
     m_reg_info.num_fpr_registers = k_num_fpr_registers_i386;
     m_reg_info.num_avx_registers = k_num_avx_registers_i386;
     m_reg_info.num_mpx_registers = k_num_mpx_registers_i386;
case llvm::Triple::x86_64:
     m_reg_info.first_dr = lldb_dr0_x86_64;
     m_reg_info.gpr_flags = lldb_rflags_x86_64;
     break;
   default:
     assert(false && "Unhandled target architecture.");
     break;
   }
 
-  // Initialize m_iovec to point to the buffer and buffer size using the
-  // conventions of Berkeley style UIO structures, as required by PTRACE
-  // extensions.
-  m_iovec.iov_base = &m_fpr;
-  m_iovec.iov_len = sizeof(m_fpr);
+  std::size_t xstate_size = GetXSTATESize();
+  m_xstate.reset(static_cast<FPR *>(std::malloc(xstate_size)));
+  m_iovec.iov_base = m_xstate.get();
+  m_iovec.iov_len = xstate_size;
 
   // Clear out the FPR state.
-  ::memset(&m_fpr, 0, sizeof(m_fpr));
+  ::memset(m_xstate.get(), 0, xstate_size);
 
   // Store byte offset of fctrl (i.e. first register of FPR)
   const RegisterInfo *reg_info_fctrl = GetRegisterInfoByName("fctrl");
   m_fctrl_offset_in_userarea = reg_info_fctrl->byte_offset;
 }
 
 // CONSIDER after local and llgs debugging are merged, register set support can
 // be moved into a base x86-64 class with IsRegisterSetAvailable made virtual.
if (IsFPR(reg) || IsAVX(reg) || IsMPX(reg)) {
     return error;
   }
 
   if (reg_info->encoding == lldb::eEncodingVector) {
     lldb::ByteOrder byte_order = GetByteOrder();
 
     if (byte_order != lldb::eByteOrderInvalid) {
       if (reg >= m_reg_info.first_st && reg <= m_reg_info.last_st)
-        reg_value.SetBytes(m_fpr.fxsave.stmm[reg - m_reg_info.first_st].bytes,
-                           reg_info->byte_size, byte_order);
+        reg_value.SetBytes(
+            m_xstate->fxsave.stmm[reg - m_reg_info.first_st].bytes,
       if (reg >= m_reg_info.first_mm && reg <= m_reg_info.last_mm)
-        reg_value.SetBytes(m_fpr.fxsave.stmm[reg - m_reg_info.first_mm].bytes,
-                           reg_info->byte_size, byte_order);
+        reg_value.SetBytes(
+            m_xstate->fxsave.stmm[reg - m_reg_info.first_mm].bytes,
       if (reg >= m_reg_info.first_xmm && reg <= m_reg_info.last_xmm)
-        reg_value.SetBytes(m_fpr.fxsave.xmm[reg - m_reg_info.first_xmm].bytes,
-                           reg_info->byte_size, byte_order);
+        reg_value.SetBytes(
+            m_xstate->fxsave.xmm[reg - m_reg_info.first_xmm].bytes,
       if (reg >= m_reg_info.first_ymm && reg <= m_reg_info.last_ymm) {
         // Concatenate ymm using the register halves in xmm.bytes and
         // ymmh.bytes
         if (CopyXSTATEtoYMM(reg, byte_order))
           reg_value.SetBytes(m_ymm_set.ymm[reg - m_reg_info.first_ymm].bytes,
                              reg_info->byte_size, byte_order);
         else {
           error.SetErrorString("failed to copy ymm register value");
if (byte_order != lldb::eByteOrderInvalid) {
 
       return error;
     }
 
     error.SetErrorString("byte order is invalid");
     return error;
   }
 
-  // Get pointer to m_fpr.fxsave variable and set the data from it.
+  // Get pointer to m_xstate->fxsave variable and set the data from it.
 
   // Byte offsets of all registers are calculated wrt 'UserArea' structure.
   // However, ReadFPR() reads fpu registers {using ptrace(PTRACE_GETFPREGS,..)}
   // and stores them in 'm_fpr' (of type FPR structure). To extract values of
   // fpu registers, m_fpr should be read at byte offsets calculated wrt to FPR
   // structure.
 
   // Since, FPR structure is also one of the member of UserArea structure.
   // byte_offset(fpu wrt FPR) = byte_offset(fpu wrt UserArea) -
   // byte_offset(fctrl wrt UserArea)
-  assert((reg_info->byte_offset - m_fctrl_offset_in_userarea) < sizeof(m_fpr));
-  uint8_t *src =
-      (uint8_t *)&m_fpr + reg_info->byte_offset - m_fctrl_offset_in_userarea;
+  assert((reg_info->byte_offset - m_fctrl_offset_in_userarea) < sizeof(FPR));
+  uint8_t *src = (uint8_t *)m_xstate.get() + reg_info->byte_offset -
+                 m_fctrl_offset_in_userarea;
   switch (reg_info->byte_size) {
   case 1:
     reg_value.SetUInt8(*(uint8_t *)src);
     break;
   case 2:
     reg_value.SetUInt16(*(uint16_t *)src);
     break;
   case 4:
default:
     break;
   }
 
   return error;
 }
 
 void NativeRegisterContextLinux_x86_64::UpdateXSTATEforWrite(
     uint32_t reg_index) {
-  XSAVE_HDR::XFeature &xstate_bv = m_fpr.xsave.header.xstate_bv;
+  XSAVE_HDR::XFeature &xstate_bv = m_xstate->xsave.header.xstate_bv;
   if (IsFPR(reg_index)) {
     // IsFPR considers both %st and %xmm registers as floating point, but these
     // map to two features. Set both flags, just in case.
     xstate_bv |= XSAVE_HDR::XFeature::FP | XSAVE_HDR::XFeature::SSE;
   } else if (IsAVX(reg_index)) {
     // Lower bytes of some %ymm registers are shared with %xmm registers.
     xstate_bv |= XSAVE_HDR::XFeature::YMM | XSAVE_HDR::XFeature::SSE;
   } else if (IsMPX(reg_index)) {
Status NativeRegisterContextLinux_x86_64::WriteRegister(
   UpdateXSTATEforWrite(reg_index);
 
   if (IsGPR(reg_index))
     return WriteRegisterRaw(reg_index, reg_value);
 
   if (IsFPR(reg_index) || IsAVX(reg_index) || IsMPX(reg_index)) {
     if (reg_info->encoding == lldb::eEncodingVector) {
       if (reg_index >= m_reg_info.first_st && reg_index <= m_reg_info.last_st)
-        ::memcpy(m_fpr.fxsave.stmm[reg_index - m_reg_info.first_st].bytes,
+        ::memcpy(m_xstate->fxsave.stmm[reg_index - m_reg_info.first_st].bytes,
                  reg_value.GetBytes(), reg_value.GetByteSize());
 
       if (reg_index >= m_reg_info.first_mm && reg_index <= m_reg_info.last_mm)
-        ::memcpy(m_fpr.fxsave.stmm[reg_index - m_reg_info.first_mm].bytes,
+        ::memcpy(m_xstate->fxsave.stmm[reg_index - m_reg_info.first_mm].bytes,
                  reg_value.GetBytes(), reg_value.GetByteSize());
 
       if (reg_index >= m_reg_info.first_xmm && reg_index <= m_reg_info.last_xmm)
-        ::memcpy(m_fpr.fxsave.xmm[reg_index - m_reg_info.first_xmm].bytes,
+        ::memcpy(m_xstate->fxsave.xmm[reg_index - m_reg_info.first_xmm].bytes,
                  reg_value.GetBytes(), reg_value.GetByteSize());
 
       if (reg_index >= m_reg_info.first_ymm &&
           reg_index <= m_reg_info.last_ymm) {
         // Store ymm register content, and split into the register halves in
         // xmm.bytes and ymmh.bytes
         ::memcpy(m_ymm_set.ymm[reg_index - m_reg_info.first_ymm].bytes,
                  reg_value.GetBytes(), reg_value.GetByteSize());
if (reg_info->encoding == lldb::eEncodingVector) {
       if (reg_index >= m_reg_info.first_mpxc &&
           reg_index <= m_reg_info.last_mpxc) {
         ::memcpy(m_mpx_set.mpxc[reg_index - m_reg_info.first_mpxc].bytes,
                  reg_value.GetBytes(), reg_value.GetByteSize());
         if (!CopyMPXtoXSTATE(reg_index))
           return Status("CopyMPXtoXSTATE() failed");
       }
     } else {
-      // Get pointer to m_fpr.fxsave variable and set the data to it.
+      // Get pointer to m_xstate->fxsave variable and set the data to it.
 
       // Byte offsets of all registers are calculated wrt 'UserArea' structure.
       // However, WriteFPR() takes m_fpr (of type FPR structure) and writes
       // only fpu registers using ptrace(PTRACE_SETFPREGS,..) API. Hence fpu
       // registers should be written in m_fpr at byte offsets calculated wrt
       // FPR structure.
 
       // Since, FPR structure is also one of the member of UserArea structure.
       // byte_offset(fpu wrt FPR) = byte_offset(fpu wrt UserArea) -
       // byte_offset(fctrl wrt UserArea)
       assert((reg_info->byte_offset - m_fctrl_offset_in_userarea) <
-             sizeof(m_fpr));
-      uint8_t *dst = (uint8_t *)&m_fpr + reg_info->byte_offset -
+             sizeof(FPR));
+      uint8_t *dst = (uint8_t *)m_xstate.get() + reg_info->byte_offset -
                      m_fctrl_offset_in_userarea;
       switch (reg_info->byte_size) {
       case 1:
         *(uint8_t *)dst = reg_value.GetAsUInt8();
         break;
       case 2:
         *(uint16_t *)dst = reg_value.GetAsUInt16();
         break;
Status NativeRegisterContextLinux_x86_64::ReadAllRegisterValues(
   error = ReadFPR();
   if (error.Fail())
     return error;
 
   uint8_t *dst = data_sp->GetBytes();
   ::memcpy(dst, &m_gpr_x86_64, GetRegisterInfoInterface().GetGPRSize());
   dst += GetRegisterInfoInterface().GetGPRSize();
   if (m_xstate_type == XStateType::FXSAVE)
-    ::memcpy(dst, &m_fpr.fxsave, sizeof(m_fpr.fxsave));
+    ::memcpy(dst, &m_xstate->fxsave, sizeof(m_xstate->fxsave));
   else if (m_xstate_type == XStateType::XSAVE) {
     lldb::ByteOrder byte_order = GetByteOrder();
 
     if (IsCPUFeatureAvailable(RegSet::avx)) {
       // Assemble the YMM register content from the register halves.
       for (uint32_t reg = m_reg_info.first_ymm; reg <= m_reg_info.last_ymm;
            ++reg) {
         if (!CopyXSTATEtoYMM(reg, byte_order)) {
if (IsCPUFeatureAvailable(RegSet::mpx)) {
               "CopyXSTATEtoMPX() failed for reg num "
               "%" PRIu32,
               __FUNCTION__, reg);
           return error;
         }
       }
     }
     // Copy the extended register state including the assembled ymm registers.
-    ::memcpy(dst, &m_fpr, sizeof(m_fpr));
+    ::memcpy(dst, m_xstate.get(), sizeof(FPR));
   } else {
     assert(false && "how do we save the floating point registers?");
     error.SetErrorString("unsure how to save the floating point registers");
   }
   /** The following code is specific to Linux x86 based architectures,
    *  where the register orig_eax (32 bit)/orig_rax (64 bit) is set to
    *  -1 to solve the bug 23659, such a setting prevents the automatic
    *  decrement of the instruction pointer which was causing the SIGILL
Status NativeRegisterContextLinux_x86_64::WriteAllRegisterValues(
   ::memcpy(&m_gpr_x86_64, src, GetRegisterInfoInterface().GetGPRSize());
 
   error = WriteGPR();
   if (error.Fail())
     return error;
 
   src += GetRegisterInfoInterface().GetGPRSize();
   if (m_xstate_type == XStateType::FXSAVE)
-    ::memcpy(&m_fpr.fxsave, src, sizeof(m_fpr.fxsave));
+    ::memcpy(&m_xstate->fxsave, src, sizeof(m_xstate->fxsave));
   else if (m_xstate_type == XStateType::XSAVE)
-    ::memcpy(&m_fpr.xsave, src, sizeof(m_fpr.xsave));
+    ::memcpy(&m_xstate->xsave, src, sizeof(m_xstate->xsave));
 
   error = WriteFPR();
   if (error.Fail())
     return error;
 
   if (m_xstate_type == XStateType::XSAVE) {
     lldb::ByteOrder byte_order = GetByteOrder();
 
if (const_cast<NativeRegisterContextLinux_x86_64 *>(this)->ReadFPR().Fail())
       return false;
   }
   switch (feature_code) {
   case RegSet::gpr:
   case RegSet::fpu:
     return true;
   case RegSet::avx: // Check if CPU has AVX and if there is kernel support, by
                     // reading in the XCR0 area of XSAVE.
-    if ((m_fpr.xsave.i387.xcr0 & mask_XSTATE_AVX) == mask_XSTATE_AVX)
+    if ((m_xstate->xsave.i387.xcr0 & mask_XSTATE_AVX) == mask_XSTATE_AVX)
       return true;
      break;
   case RegSet::mpx: // Check if CPU has MPX and if there is kernel support, by
                     // reading in the XCR0 area of XSAVE.
-    if ((m_fpr.xsave.i387.xcr0 & mask_XSTATE_MPX) == mask_XSTATE_MPX)
+    if ((m_xstate->xsave.i387.xcr0 & mask_XSTATE_MPX) == mask_XSTATE_MPX)
       return true;
     break;
   }
   return false;
 }
 
 bool NativeRegisterContextLinux_x86_64::IsRegisterSetAvailable(
     uint32_t set_index) const {
bool NativeRegisterContextLinux_x86_64::IsFPR(uint32_t reg_index) const {
   return (m_reg_info.first_fpr <= reg_index &&
           reg_index <= m_reg_info.last_fpr);
 }
 
 Status NativeRegisterContextLinux_x86_64::WriteFPR() {
   switch (m_xstate_type) {
   case XStateType::FXSAVE:
     return WriteRegisterSet(
-        &m_iovec, sizeof(m_fpr.fxsave),
+        &m_iovec, sizeof(m_xstate->fxsave),
         fxsr_regset(GetRegisterInfoInterface().GetTargetArchitecture()));
   case XStateType::XSAVE:
-    return WriteRegisterSet(&m_iovec, sizeof(m_fpr.xsave), NT_X86_XSTATE);
+    return WriteRegisterSet(&m_iovec, sizeof(m_xstate->xsave), NT_X86_XSTATE);
   default:
     return Status("Unrecognized FPR type.");
   }
 }
 
 bool NativeRegisterContextLinux_x86_64::IsAVX(uint32_t reg_index) const {
   if (!IsCPUFeatureAvailable(RegSet::avx))
     return false;
   return (m_reg_info.first_ymm <= reg_index &&
           reg_index <= m_reg_info.last_ymm);
 }
 
 bool NativeRegisterContextLinux_x86_64::CopyXSTATEtoYMM(
     uint32_t reg_index, lldb::ByteOrder byte_order) {
   if (!IsAVX(reg_index))
     return false;
 
   if (byte_order == lldb::eByteOrderLittle) {
     ::memcpy(m_ymm_set.ymm[reg_index - m_reg_info.first_ymm].bytes,
-             m_fpr.fxsave.xmm[reg_index - m_reg_info.first_ymm].bytes,
+             m_xstate->fxsave.xmm[reg_index - m_reg_info.first_ymm].bytes,
              sizeof(XMMReg));
     ::memcpy(m_ymm_set.ymm[reg_index - m_reg_info.first_ymm].bytes +
                  sizeof(XMMReg),
-             m_fpr.xsave.ymmh[reg_index - m_reg_info.first_ymm].bytes,
+             m_xstate->xsave.ymmh[reg_index - m_reg_info.first_ymm].bytes,
              sizeof(YMMHReg));
     return true;
   }
 
   if (byte_order == lldb::eByteOrderBig) {
     ::memcpy(m_ymm_set.ymm[reg_index - m_reg_info.first_ymm].bytes +
                  sizeof(XMMReg),
-             m_fpr.fxsave.xmm[reg_index - m_reg_info.first_ymm].bytes,
+             m_xstate->fxsave.xmm[reg_index - m_reg_info.first_ymm].bytes,
              sizeof(XMMReg));
     ::memcpy(m_ymm_set.ymm[reg_index - m_reg_info.first_ymm].bytes,
-             m_fpr.xsave.ymmh[reg_index - m_reg_info.first_ymm].bytes,
+             m_xstate->xsave.ymmh[reg_index - m_reg_info.first_ymm].bytes,
              sizeof(YMMHReg));
     return true;
   }
   return false; // unsupported or invalid byte order
 }
 
 bool NativeRegisterContextLinux_x86_64::CopyYMMtoXSTATE(
     uint32_t reg, lldb::ByteOrder byte_order) {
   if (!IsAVX(reg))
     return false;
 
   if (byte_order == lldb::eByteOrderLittle) {
-    ::memcpy(m_fpr.fxsave.xmm[reg - m_reg_info.first_ymm].bytes,
+    ::memcpy(m_xstate->fxsave.xmm[reg - m_reg_info.first_ymm].bytes,
              m_ymm_set.ymm[reg - m_reg_info.first_ymm].bytes, sizeof(XMMReg));
-    ::memcpy(m_fpr.xsave.ymmh[reg - m_reg_info.first_ymm].bytes,
+    ::memcpy(m_xstate->xsave.ymmh[reg - m_reg_info.first_ymm].bytes,
              m_ymm_set.ymm[reg - m_reg_info.first_ymm].bytes + sizeof(XMMReg),
              sizeof(YMMHReg));
     return true;
   }
 
   if (byte_order == lldb::eByteOrderBig) {
-    ::memcpy(m_fpr.fxsave.xmm[reg - m_reg_info.first_ymm].bytes,
+    ::memcpy(m_xstate->fxsave.xmm[reg - m_reg_info.first_ymm].bytes,
              m_ymm_set.ymm[reg - m_reg_info.first_ymm].bytes + sizeof(XMMReg),
              sizeof(XMMReg));
-    ::memcpy(m_fpr.xsave.ymmh[reg - m_reg_info.first_ymm].bytes,
+    ::memcpy(m_xstate->xsave.ymmh[reg - m_reg_info.first_ymm].bytes,
              m_ymm_set.ymm[reg - m_reg_info.first_ymm].bytes, sizeof(YMMHReg));
     return true;
   }
   return false; // unsupported or invalid byte order
 }
 
 void *NativeRegisterContextLinux_x86_64::GetFPRBuffer() {
   switch (m_xstate_type) {
   case XStateType::FXSAVE:
-    return &m_fpr.fxsave;
+    return &m_xstate->fxsave;
   case XStateType::XSAVE:
     return &m_iovec;
   default:
     return nullptr;
   }
 }
 
 size_t NativeRegisterContextLinux_x86_64::GetFPRSize() {
   switch (m_xstate_type) {
   case XStateType::FXSAVE:
-    return sizeof(m_fpr.fxsave);
+    return sizeof(m_xstate->fxsave);
   case XStateType::XSAVE:
     return sizeof(m_iovec);
   default:
     return 0;
   }
 }
 
 Status NativeRegisterContextLinux_x86_64::ReadFPR() {
   Status error;
 
   // Probe XSAVE and if it is not supported fall back to FXSAVE.
   if (m_xstate_type != XStateType::FXSAVE) {
-    error = ReadRegisterSet(&m_iovec, sizeof(m_fpr.xsave), NT_X86_XSTATE);
+    error = ReadRegisterSet(&m_iovec, sizeof(m_xstate->xsave), NT_X86_XSTATE);
     if (!error.Fail()) {
       m_xstate_type = XStateType::XSAVE;
       return error;
     }
   }
   error = ReadRegisterSet(
-      &m_iovec, sizeof(m_fpr.xsave),
+      &m_iovec, sizeof(m_xstate->xsave),
       fxsr_regset(GetRegisterInfoInterface().GetTargetArchitecture()));
   if (!error.Fail()) {
     m_xstate_type = XStateType::FXSAVE;
     return error;
   }
   return Status("Unrecognized FPR type.");
 }
 
 bool NativeRegisterContextLinux_x86_64::IsMPX(uint32_t reg_index) const {
   if (!IsCPUFeatureAvailable(RegSet::mpx))
     return false;
   return (m_reg_info.first_mpxr <= reg_index &&
           reg_index <= m_reg_info.last_mpxc);
 }
 
 bool NativeRegisterContextLinux_x86_64::CopyXSTATEtoMPX(uint32_t reg) {
   if (!IsMPX(reg))
     return false;
 
   if (reg >= m_reg_info.first_mpxr && reg <= m_reg_info.last_mpxr) {
     ::memcpy(m_mpx_set.mpxr[reg - m_reg_info.first_mpxr].bytes,
-             m_fpr.xsave.mpxr[reg - m_reg_info.first_mpxr].bytes,
+             m_xstate->xsave.mpxr[reg - m_reg_info.first_mpxr].bytes,
              sizeof(MPXReg));
   } else {
     ::memcpy(m_mpx_set.mpxc[reg - m_reg_info.first_mpxc].bytes,
-             m_fpr.xsave.mpxc[reg - m_reg_info.first_mpxc].bytes,
+             m_xstate->xsave.mpxc[reg - m_reg_info.first_mpxc].bytes,
              sizeof(MPXCsr));
   }
   return true;
 }
 
 bool NativeRegisterContextLinux_x86_64::CopyMPXtoXSTATE(uint32_t reg) {
   if (!IsMPX(reg))
     return false;
 
   if (reg >= m_reg_info.first_mpxr && reg <= m_reg_info.last_mpxr) {
-    ::memcpy(m_fpr.xsave.mpxr[reg - m_reg_info.first_mpxr].bytes,
+    ::memcpy(m_xstate->xsave.mpxr[reg - m_reg_info.first_mpxr].bytes,
              m_mpx_set.mpxr[reg - m_reg_info.first_mpxr].bytes, sizeof(MPXReg));
   } else {
-    ::memcpy(m_fpr.xsave.mpxc[reg - m_reg_info.first_mpxc].bytes,
+    ::memcpy(m_xstate->xsave.mpxc[reg - m_reg_info.first_mpxc].bytes,
              m_mpx_set.mpxc[reg - m_reg_info.first_mpxc].bytes, sizeof(MPXCsr));
   }
   return true;
 }
 
 Status NativeRegisterContextLinux_x86_64::IsWatchpointHit(uint32_t wp_index,
                                                           bool &is_hit) {
   if (wp_index >= NumSupportedHardwareWatchpoints())