[LLDB] Fix out-of-bounds memory access in EmulationStateArm

[fixathon]

Summary

Functionally broken code for reading and writing registers, likely due to typos,
and could cause out-of-bounds memory access.

[DavidSpickett]

LGTM and I'll add a test later that would break without this fix.

[fixathon]

Thank you. Yes, this does need a unit test

lldb/source/Plugins/Instruction/ARM/EmulationStateARM.cpp

54

Here index 'i' represents an offset starting at dwarf_d0, and index 'idx' is normalized to start at 0.
"i" will always be greater than 16 causing the 'else' statement to always execute regardless of the intent.

95

Also clearly a typo as can be seen from the if condition, and the corresponding store code.

lldb/source/Plugins/Instruction/ARM/EmulationStateARM.cpp

for (int i = dwarf_d0; i < dwarf_d0 + 32; ++i) {
     reg_num =
         reg_ctx->ConvertRegisterKindToRegisterNumber(eRegisterKindDWARF, i);
     RegisterValue reg_value;
     const RegisterInfo *reg_info = reg_ctx->GetRegisterInfoAtIndex(reg_num);
 
     if (reg_ctx->ReadRegister(reg_info, reg_value)) {
       uint64_t value = reg_value.GetAsUInt64();
       uint32_t idx = i - dwarf_d0;
-      if (i < 16) {
+      if (idx < 16) {
         m_vfp_regs.s_regs[idx * 2] = (uint32_t)value;
         m_vfp_regs.s_regs[idx * 2 + 1] = (uint32_t)(value >> 32);
       } else
         m_vfp_regs.d_regs[idx - 16] = value;
     } else
       success = false;
   }
 
uint64_t EmulationStateARM::ReadPseudoRegisterValue(uint32_t reg_num,
                                                     bool &success) {
   uint64_t value = 0;
   success = true;
 
   if (reg_num <= dwarf_cpsr)
     value = m_gpr[reg_num - dwarf_r0];
   else if ((dwarf_s0 <= reg_num) && (reg_num <= dwarf_s31)) {
     uint32_t idx = reg_num - dwarf_s0;
-    value = m_vfp_regs.d_regs[idx];
+    value = m_vfp_regs.s_regs[idx];
   } else if ((dwarf_d0 <= reg_num) && (reg_num <= dwarf_d31)) {
     uint32_t idx = reg_num - dwarf_d0;
     if (idx < 16)
       value = (uint64_t)m_vfp_regs.s_regs[idx * 2] |
               ((uint64_t)m_vfp_regs.s_regs[idx * 2 + 1] << 32);
     else
       value = m_vfp_regs.d_regs[idx - 16];
   } else