[llvm] [Dexter] Use continue when resuming lldb execution to reach breakpoint (PR #156481)

[Stephen Tozer via llvm-commits]

https://github.com/SLTozer created https://github.com/llvm/llvm-project/pull/156481

Currently, Dexter's interface for lldb and lldb-dap has a post-step hook that checks to see whether lldb reports that we stopped because we completed a step, and if so checks to see whether the current $pc address also matches a known breakpoint whose conditions (if any) are met, and if so it requests to "step in", so that we "resume" execution, stopping again at the current address, such that lldb now reports that we have hit a breakpoint and provides the list of breakpoints that were hit.

This logic has a flaw however: the call to "step in" sets an implicit breakpoint on the next line. In Dexter's default stepping mode this is not an issue, as we intend to step there eventually. When we use DexContinue, however, we set a breakpoint from which we wish to continue to the next user-specified breakpoint, rather than stepping. Currently, there is a bug where Dexter sets a DexContinue breakpoint, arrives at that bp from a step, requests "step in" so that LLDB gives us the hit breakpoint ID, requests "continue" to hit the next user breakpoint, and then arrives at the next line after the continue due to the earlier "step in" request. This effectively negates the DexContinue command.

This patch fixes this behaviour by using "continue" instead of "step in" in the post-step hook, ensuring that no implicit breakpoint is set so that we do not incorrectly stop at the next line.

Likely fixes the issue reported at: https://github.com/llvm/llvm-project/pull/152721#issuecomment-3242907059

>From fac05cf25ab0a8e0cd91a3dc975ad56fde0dcfd7 Mon Sep 17 00:00:00 2001
From: Stephen Tozer <stephen.tozer at sony.com>
Date: Tue, 2 Sep 2025 16:51:18 +0100
Subject: [PATCH] [Dexter] Use continue when resuming lldb execution to reach
 breakpoint

Currently, Dexter's interface for lldb and lldb-dap has a post-step hook
that checks to see whether lldb reports that we stopped because we
completed a step, and if so checks to see whether the current $pc address
also matches a known breakpoint whose conditions (if any) are met, and if
so it requests to "step in", so that we "resume" execution, stopping again
at the current address, such that lldb now reports that we have hit a
breakpoint and provides the list of breakpoints that were hit.

This logic has a flaw however: the call to "step in" sets an implicit
breakpoint on the next line. In Dexter's default stepping mode this is not
an issue, as we intend to step there eventually. When we use DexContinue,
however, we set a breakpoint from which we wish to continue to the next
user-specified breakpoint, rather than stepping. Currently, there is a bug
where Dexter sets a DexContinue breakpoint, arrives at that bp from a step,
requests "step in" so that LLDB gives us the hit breakpoint ID, requests
"continue" to hit the next user breakpoint, and then arrives at the next
line after the continue due to the earlier "step in" request. This
effectively negates the DexContinue command.

This patch fixes this behaviour by using "continue" instead of "step in" in
the post-step hook, ensuring that no implicit breakpoint is set so that we
do not incorrectly stop at the next line.
---
 .../debuginfo-tests/dexter/dex/debugger/lldb/LLDB.py          | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/cross-project-tests/debuginfo-tests/dexter/dex/debugger/lldb/LLDB.py b/cross-project-tests/debuginfo-tests/dexter/dex/debugger/lldb/LLDB.py
index dec12b9bc83da..e3d0c4ec192d3 100644
--- a/cross-project-tests/debuginfo-tests/dexter/dex/debugger/lldb/LLDB.py
+++ b/cross-project-tests/debuginfo-tests/dexter/dex/debugger/lldb/LLDB.py
@@ -232,7 +232,7 @@ def step_in(self):
                     ):
                         stepped_to_breakpoint = True
             if stepped_to_breakpoint:
-                self._thread.StepInto()
+                self._thread.Continue()
 
     def go(self) -> ReturnCode:
         self._process.Continue()
@@ -441,7 +441,7 @@ def _post_step_hook(self):
                 # Step again now to get to the breakpoint.
                 step_req_id = self.send_message(
                     self.make_request(
-                        "stepIn", {"threadId": self._debugger_state.thread}
+                        "continue", {"threadId": self._debugger_state.thread}
                     )
                 )
                 response = self._await_response(step_req_id)