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

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

Differential Revision: https://reviews.llvm.org/D83343

Signed-off-by: Med Ismail Bennani <[email protected]>

Author: medismailben

lldb/source/API/SBFrame.cpp

@@ -354,15 +354,15 @@ bool SBFrame::SetPC(addr_t new_pc) {
   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) {
-        ret_val = frame->GetRegisterContext()->SetPC(new_pc);
+      if (StackFrame *frame = exe_ctx.GetFramePtr()) {
+        if (RegisterContextSP reg_ctx_sp = frame->GetRegisterContext()) {
+          ret_val = reg_ctx_sp->SetPC(new_pc);
+        }
       }
     }
   }
@@ -377,15 +377,15 @@ addr_t SBFrame::GetSP() const {
   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();
+      if (StackFrame *frame = exe_ctx.GetFramePtr()) {
+        if (RegisterContextSP reg_ctx_sp = frame->GetRegisterContext()) {
+          addr = reg_ctx_sp->GetSP();
+        }
       }
     }
   }
@@ -400,15 +400,16 @@ addr_t SBFrame::GetFP() const {
   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()->GetFP();
+      if (StackFrame *frame = exe_ctx.GetFramePtr()) {
+        if (RegisterContextSP reg_ctx_sp = frame->GetRegisterContext()) {
+          addr = reg_ctx_sp->GetFP();
+        }
+      }
     }
   }