Bug 25050: X87 FPU Special Purpose Registers

Summary:
  - For x86_64-FreeBSD Platform:
    -- LLDB now provides correct values of X87 FPU
       Special Purpose Registers like fstat, ftag, fctrl etc..

Signed-off-by: Abhishek Aggarwal <abhishek.a.aggarwal@intel.com>

Reviewers: emaste, mikesart, clayborg

Subscribers: emaste

Differential Revision: http://reviews.llvm.org/D13434

llvm-svn: 249379

2 files changed, 22 insertions, 4 deletions

diff --git a/lldb/source/Plugins/Process/FreeBSD/RegisterContextPOSIXProcessMonitor_x86.cpp b/lldb/source/Plugins/Process/FreeBSD/RegisterContextPOSIXProcessMonitor_x86.cpp
index 67dc21cb48e..a77f9427af4 100644
--- a/lldb/source/Plugins/Process/FreeBSD/RegisterContextPOSIXProcessMonitor_x86.cpp
+++ b/lldb/source/Plugins/Process/FreeBSD/RegisterContextPOSIXProcessMonitor_x86.cpp
@@ -58,6 +58,9 @@ RegisterContextPOSIXProcessMonitor_x86_64::RegisterContextPOSIXProcessMonitor_x8
                                                                                      lldb_private::RegisterInfoInterface *register_info)
     : RegisterContextPOSIX_x86(thread, concrete_frame_idx, register_info)
 {
+    // Store byte offset of fctrl (i.e. first register of FPR) wrt 'UserArea'
+    const RegisterInfo *reg_info_fctrl = GetRegisterInfoByName("fctrl");
+    m_fctrl_offset_in_userarea = reg_info_fctrl->byte_offset;
 }
 
 ProcessMonitor &
@@ -254,8 +257,15 @@ RegisterContextPOSIXProcessMonitor_x86_64::ReadRegister(const RegisterInfo *reg_
     }
 
     // Get pointer to m_fpr.xstate.fxsave variable and set the data from it.
-    assert (reg_info->byte_offset < sizeof(m_fpr));
-    uint8_t *src = (uint8_t *)&m_fpr + reg_info->byte_offset; 
+    // Byte offsets of all registers are calculated wrt 'UserArea' structure.
+    // However, ReadFPR() reads fpu registers {using ptrace(PT_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;
     switch (reg_info->byte_size)
     {
         case 2:
@@ -308,8 +318,15 @@ RegisterContextPOSIXProcessMonitor_x86_64::WriteRegister(const RegisterInfo *reg
         else
         {
             // Get pointer to m_fpr.xstate.fxsave variable and set the data to it.
-            assert (reg_info->byte_offset < sizeof(m_fpr));
-            uint8_t *dst = (uint8_t *)&m_fpr + reg_info->byte_offset; 
+            // 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(PT_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 - m_fctrl_offset_in_userarea;
             switch (reg_info->byte_size)
             {
                 case 2:
diff --git a/lldb/source/Plugins/Process/FreeBSD/RegisterContextPOSIXProcessMonitor_x86.h b/lldb/source/Plugins/Process/FreeBSD/RegisterContextPOSIXProcessMonitor_x86.h
index db6c7c5e2a3..f55d917ee75 100644
--- a/lldb/source/Plugins/Process/FreeBSD/RegisterContextPOSIXProcessMonitor_x86.h
+++ b/lldb/source/Plugins/Process/FreeBSD/RegisterContextPOSIXProcessMonitor_x86.h
@@ -91,6 +91,7 @@ protected:
 private:
     ProcessMonitor &
     GetMonitor();
+    uint32_t m_fctrl_offset_in_userarea;  // Offset of 'fctrl' in 'UserArea' Structure
 };
 
 #endif