[lldb/api] Add checks for StackFrame::GetRegisterContext calls (NFC)

[mib]

Summary

This patch fixes a crash that is happening because of a null pointer
dereference in SBFrame.

StackFrame::GetRegisterContext says explicitly that you might not get
a valid RegisterContext back but the pointer wasn't tested before,
resulting in crashes. This should solve the issue.

rdar://54462095

Signed-off-by: Med Ismail Bennani <[e-mail]>

[mib]

Changed style.

[JDevlieghere]

A test would be great but since we can't repro this is strictly better than the current state. LGTM.

lldb/source/API/SBFrame.cpp

 //===-- SBFrame.cpp -------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include <algorithm>
 #include <set>
 #include <string>
 
 #include "lldb/API/SBFrame.h"
 
 #include "lldb/lldb-types.h"
 
 #include "SBReproducerPrivate.h"
 #include "Utils.h"
 #include "lldb/Core/Address.h"
 #include "lldb/Core/StreamFile.h"
 #include "lldb/Core/ValueObjectRegister.h"
bool SBFrame::SetPC(addr_t new_pc) {
 
   StackFrame *frame = nullptr;
   Target *target = exe_ctx.GetTargetPtr();
   Process *process = exe_ctx.GetProcessPtr();
   if (target && process) {
     Process::StopLocker stop_locker;
     if (stop_locker.TryLock(&process->GetRunLock())) {
       frame = exe_ctx.GetFramePtr();
-      if (frame) {
-        ret_val = frame->GetRegisterContext()->SetPC(new_pc);
-      }
+      RegisterContextSP reg_ctx_sp = nullptr;
+      if (frame)
+        reg_ctx_sp = frame->GetRegisterContext();
+      if (reg_ctx_sp)
+        ret_val = reg_ctx_sp->SetPC(new_pc);
     }
   }
 
   return ret_val;
 }
 
 addr_t SBFrame::GetSP() const {
   LLDB_RECORD_METHOD_CONST_NO_ARGS(lldb::addr_t, SBFrame, GetSP);
 
   addr_t addr = LLDB_INVALID_ADDRESS;
   std::unique_lock<std::recursive_mutex> lock;
   ExecutionContext exe_ctx(m_opaque_sp.get(), lock);
 
   StackFrame *frame = nullptr;
   Target *target = exe_ctx.GetTargetPtr();
   Process *process = exe_ctx.GetProcessPtr();
   if (target && process) {
     Process::StopLocker stop_locker;
     if (stop_locker.TryLock(&process->GetRunLock())) {
       frame = exe_ctx.GetFramePtr();
-      if (frame) {
-        addr = frame->GetRegisterContext()->GetSP();
-      }
+      RegisterContextSP reg_ctx_sp = nullptr;
+      if (frame)
+        reg_ctx_sp = frame->GetRegisterContext();
+      if (reg_ctx_sp)
+        addr = reg_ctx_sp->GetSP();
     }
   }
 
   return addr;
 }
 
 addr_t SBFrame::GetFP() const {
   LLDB_RECORD_METHOD_CONST_NO_ARGS(lldb::addr_t, SBFrame, GetFP);
 
   addr_t addr = LLDB_INVALID_ADDRESS;
   std::unique_lock<std::recursive_mutex> lock;
   ExecutionContext exe_ctx(m_opaque_sp.get(), lock);
 
   StackFrame *frame = nullptr;
   Target *target = exe_ctx.GetTargetPtr();
   Process *process = exe_ctx.GetProcessPtr();
   if (target && process) {
     Process::StopLocker stop_locker;
     if (stop_locker.TryLock(&process->GetRunLock())) {
       frame = exe_ctx.GetFramePtr();
+      RegisterContextSP reg_ctx_sp = nullptr;
       if (frame)
-        addr = frame->GetRegisterContext()->GetFP();
+        reg_ctx_sp = frame->GetRegisterContext();
+      if (reg_ctx_sp)
+        addr = reg_ctx_sp->GetFP();
     }
   }
 
   return addr;
 }
 
 SBAddress SBFrame::GetPCAddress() const {
   LLDB_RECORD_METHOD_CONST_NO_ARGS(lldb::SBAddress, SBFrame, GetPCAddress);