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

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).

Reviewers: jankratochvil, davezarzycki

Subscribers: lldb-commits

Differential Revision: https://reviews.llvm.org/D59991

llvm-svn: 357376

diff --git a/lldb/source/Plugins/Process/Linux/NativeRegisterContextLinux_x86_64.cpp b/lldb/source/Plugins/Process/Linux/NativeRegisterContextLinux_x86_64.cpp
index 4963c52..b7d5b6b 100644 (file)
--- a/lldb/source/Plugins/Process/Linux/NativeRegisterContextLinux_x86_64.cpp
+++ b/lldb/source/Plugins/Process/Linux/NativeRegisterContextLinux_x86_64.cpp
@@ -18,7 +18,7 @@
 
 #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;
@@ -267,12 +267,29 @@ CreateRegisterInfoInterface(const ArchSpec &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:
@@ -328,14 +345,13 @@ NativeRegisterContextLinux_x86_64::NativeRegisterContextLinux_x86_64(
     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");
@@ -438,14 +454,17 @@ NativeRegisterContextLinux_x86_64::ReadRegister(const RegisterInfo *reg_info,
 
     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,
+            reg_info->byte_size, byte_order);
       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,
+            reg_info->byte_size, byte_order);
       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,
+            reg_info->byte_size, byte_order);
       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
@@ -487,7 +506,7 @@ NativeRegisterContextLinux_x86_64::ReadRegister(const RegisterInfo *reg_info,
     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,..)}
@@ -498,9 +517,9 @@ NativeRegisterContextLinux_x86_64::ReadRegister(const RegisterInfo *reg_info,
   // 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);
@@ -526,7 +545,7 @@ NativeRegisterContextLinux_x86_64::ReadRegister(const RegisterInfo *reg_info,
 
 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.
@@ -558,15 +577,15 @@ Status NativeRegisterContextLinux_x86_64::WriteRegister(
   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 &&
@@ -595,7 +614,7 @@ Status NativeRegisterContextLinux_x86_64::WriteRegister(
           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
@@ -607,8 +626,8 @@ Status NativeRegisterContextLinux_x86_64::WriteRegister(
       // 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:
@@ -666,7 +685,7 @@ Status NativeRegisterContextLinux_x86_64::ReadAllRegisterValues(
   ::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();
 
@@ -699,7 +718,7 @@ Status NativeRegisterContextLinux_x86_64::ReadAllRegisterValues(
       }
     }
     // 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");
@@ -757,9 +776,9 @@ Status NativeRegisterContextLinux_x86_64::WriteAllRegisterValues(
 
   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())
@@ -813,12 +832,12 @@ bool NativeRegisterContextLinux_x86_64::IsCPUFeatureAvailable(
     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;
   }
@@ -855,10 +874,10 @@ 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.");
   }
@@ -878,11 +897,11 @@ bool NativeRegisterContextLinux_x86_64::CopyXSTATEtoYMM(
 
   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;
   }
@@ -890,10 +909,10 @@ bool NativeRegisterContextLinux_x86_64::CopyXSTATEtoYMM(
   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;
   }
@@ -906,19 +925,19 @@ bool NativeRegisterContextLinux_x86_64::CopyYMMtoXSTATE(
     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;
   }
@@ -928,7 +947,7 @@ bool NativeRegisterContextLinux_x86_64::CopyYMMtoXSTATE(
 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:
@@ -939,7 +958,7 @@ void *NativeRegisterContextLinux_x86_64::GetFPRBuffer() {
 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:
@@ -952,14 +971,14 @@ Status NativeRegisterContextLinux_x86_64::ReadFPR() {
 
   // 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;
@@ -981,11 +1000,11 @@ bool NativeRegisterContextLinux_x86_64::CopyXSTATEtoMPX(uint32_t reg) {
 
   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;
@@ -996,10 +1015,10 @@ bool NativeRegisterContextLinux_x86_64::CopyMPXtoXSTATE(uint32_t 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;

diff --git a/lldb/source/Plugins/Process/Linux/NativeRegisterContextLinux_x86_64.h b/lldb/source/Plugins/Process/Linux/NativeRegisterContextLinux_x86_64.h
index 25a73db..6031ddb 100644 (file)
--- a/lldb/source/Plugins/Process/Linux/NativeRegisterContextLinux_x86_64.h
+++ b/lldb/source/Plugins/Process/Linux/NativeRegisterContextLinux_x86_64.h
@@ -108,7 +108,8 @@ private:
 
   // 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;