Add setting to require hardware breakpoints.

When debugging read-only memory we cannot use software breakpoint. We
already have support for hardware breakpoints and users can specify them
with `-H`. However, there's no option to force LLDB to use hardware
breakpoints internally, for example while stepping.

This patch adds a setting target.require-hardware-breakpoint that forces
LLDB to always use hardware breakpoints. Because hardware breakpoints
are a limited resource and can fail to resolve, this patch also extends
error handling in thread plans, where breakpoints are used for stepping.

Differential revision: https://reviews.llvm.org/D54221

llvm-svn: 346920

1 files changed, 24 insertions, 1 deletions

diff --git a/lldb/source/Target/ThreadPlanStepThrough.cpp b/lldb/source/Target/ThreadPlanStepThrough.cpp
index b373edbf8f3..d1f3c2219f6 100644
--- a/lldb/source/Target/ThreadPlanStepThrough.cpp
+++ b/lldb/source/Target/ThreadPlanStepThrough.cpp
@@ -58,7 +58,10 @@ ThreadPlanStepThrough::ThreadPlanStepThrough(Thread &thread,
               ->GetTarget()
               .CreateBreakpoint(m_backstop_addr, true, false)
               .get();
+
       if (return_bp != nullptr) {
+        if (return_bp->IsHardware() && !return_bp->HasResolvedLocations())
+          m_could_not_resolve_hw_bp = true;
         return_bp->SetThreadID(m_thread.GetID());
         m_backstop_bkpt_id = return_bp->GetID();
         return_bp->SetBreakpointKind("step-through-backstop");
@@ -135,7 +138,26 @@ void ThreadPlanStepThrough::GetDescription(Stream *s,
 }
 
 bool ThreadPlanStepThrough::ValidatePlan(Stream *error) {
-  return m_sub_plan_sp.get() != nullptr;
+  if (m_could_not_resolve_hw_bp) {
+    if (error)
+      error->PutCString(
+          "Could not create hardware breakpoint for thread plan.");
+    return false;
+  }
+
+  if (m_backstop_bkpt_id == LLDB_INVALID_BREAK_ID) {
+    if (error)
+      error->PutCString("Could not create backstop breakpoint.");
+    return false;
+  }
+
+  if (!m_sub_plan_sp.get()) {
+    if (error)
+      error->PutCString("Does not have a subplan.");
+    return false;
+  }
+
+  return true;
 }
 
 bool ThreadPlanStepThrough::DoPlanExplainsStop(Event *event_ptr) {
@@ -211,6 +233,7 @@ void ThreadPlanStepThrough::ClearBackstopBreakpoint() {
   if (m_backstop_bkpt_id != LLDB_INVALID_BREAK_ID) {
     m_thread.GetProcess()->GetTarget().RemoveBreakpointByID(m_backstop_bkpt_id);
     m_backstop_bkpt_id = LLDB_INVALID_BREAK_ID;
+    m_could_not_resolve_hw_bp = false;
   }
 }