https://github.com/Michael137 created
https://github.com/llvm/llvm-project/pull/134097
When using `SBFrame::EvaluateExpression` on a frame that's not the currently
selected frame, we would sometimes run into errors such as:
```
error: error: The context has changed before we could JIT the expression!
error: errored out in DoExecute, couldn't PrepareToExecuteJITExpression
```
Durin expression parsing, we call `RunStaticInitializers`. On our internal fork
this happens quite frequently because any usage of, e.g., function pointers,
will inject ptrauth fixup code into the expression. The static initializers
are run using `RunThreadPlan`. The `ExecutionContext::m_frame_sp` going into
the `RunThreadPlan` is the `SBFrame` that we called `EvaluateExpression` on.
LLDB then tries to save this frame to restore it later (the restore occurs by
unconditionally overwriting whatever is in `ExecutionContext::m_frame_sp`).
However, if the `selected_frame_sp` is not the same as the `SBFrame`, then
`RunThreadPlan` would set the `ExecutionContext`'s frame to a different frame
than what we started with. When we `PrepareToExecuteJITExpression`, LLDB checks
whether the `ExecutionContext` frame changed from when we initially
`EvaluateExpression`, and if did, bails out with the error above.
One such test-case is attached. This currently passes regardless of the fix
because our ptrauth static initializers code isn't upstream yet. But the plan
is to upstream it soon.
This patch addresses the issue by saving/restoring the frame of the incoming
`ExecutionContext`, if such frame exists. Otherwise, fall back to using the
selected frame.
rdar://147456589
>From 151ad919ab6f2d87991511b293f4a9797210f82f Mon Sep 17 00:00:00 2001
From: Michael Buch <michaelbuc...@gmail.com>
Date: Wed, 2 Apr 2025 15:48:25 +0100
Subject: [PATCH] [lldb][Target] RunThreadPlan to save/restore the
ExecutionContext's frame if one exists
When using `SBFrame::EvaluateExpression` on a frame that's not the
currently selected frame, we would sometimes run into errors such as:
```
error: error: The context has changed before we could JIT the expression!
error: errored out in DoExecute, couldn't PrepareToExecuteJITExpression
```
Durin expression parsing, we call `RunStaticInitializers`. On our internal fork
this happens quite frequently because any usage of, e.g., function pointers,
will inject ptrauth fixup code into the expression. The static initializers
are run using `RunThreadPlan`. The `ExecutionContext::m_frame_sp` going into
the `RunThreadPlan` is the `SBFrame` that we called `EvaluateExpression` on.
LLDB then tries to save this frame to restore it later (the restore occurs by
unconditionally overwriting whatever is in `ExecutionContext::m_frame_sp`).
However, if the `selected_frame_sp` is not the same as the `SBFrame`, then
`RunThreadPlan` would set the `ExecutionContext`'s frame to a different frame
than what we started with. When we `PrepareToExecuteJITExpression`, LLDB checks
whether the `ExecutionContext` frame changed from when we initially
`EvaluateExpression`, and if did, bails out with the error above.
One such test-case is attached. This currently passes regardless of the fix
because our ptrauth static initializers code isn't upstream yet. But the plan
is to upstream it soon.
This patch addresses the issue by saving/restoring the frame of the incoming
`ExecutionContext`, if such frame exists. Otherwise, fall back to using the
selected frame.
---
lldb/source/Target/Process.cpp | 8 ++++-
.../expr-from-non-zero-frame/Makefile | 3 ++
.../TestExprFromNonZeroFrame.py | 29 +++++++++++++++++++
.../expr-from-non-zero-frame/main.cpp | 6 ++++
4 files changed, 45 insertions(+), 1 deletion(-)
create mode 100644
lldb/test/API/commands/expression/expr-from-non-zero-frame/Makefile
create mode 100644
lldb/test/API/commands/expression/expr-from-non-zero-frame/TestExprFromNonZeroFrame.py
create mode 100644
lldb/test/API/commands/expression/expr-from-non-zero-frame/main.cpp
diff --git a/lldb/source/Target/Process.cpp b/lldb/source/Target/Process.cpp
index 369933234ccca..f4ecb0b7ea307 100644
--- a/lldb/source/Target/Process.cpp
+++ b/lldb/source/Target/Process.cpp
@@ -5080,7 +5080,13 @@ Process::RunThreadPlan(ExecutionContext &exe_ctx,
return eExpressionSetupError;
}
- StackID ctx_frame_id = selected_frame_sp->GetStackID();
+ // If the ExecutionContext has a frame, we want to make sure to save/restore
+ // that frame into exe_ctx. This can happen when we run expressions from a
+ // non-selected SBFrame, in which case we don't want some thread-plan
+ // to overwrite the ExecutionContext frame.
+ StackID ctx_frame_id = exe_ctx.HasFrameScope()
+ ? exe_ctx.GetFrameRef().GetStackID()
+ : selected_frame_sp->GetStackID();
// N.B. Running the target may unset the currently selected thread and frame.
// We don't want to do that either, so we should arrange to reset them as
diff --git
a/lldb/test/API/commands/expression/expr-from-non-zero-frame/Makefile
b/lldb/test/API/commands/expression/expr-from-non-zero-frame/Makefile
new file mode 100644
index 0000000000000..99998b20bcb05
--- /dev/null
+++ b/lldb/test/API/commands/expression/expr-from-non-zero-frame/Makefile
@@ -0,0 +1,3 @@
+CXX_SOURCES := main.cpp
+
+include Makefile.rules
diff --git
a/lldb/test/API/commands/expression/expr-from-non-zero-frame/TestExprFromNonZeroFrame.py
b/lldb/test/API/commands/expression/expr-from-non-zero-frame/TestExprFromNonZeroFrame.py
new file mode 100644
index 0000000000000..e87279abde406
--- /dev/null
+++
b/lldb/test/API/commands/expression/expr-from-non-zero-frame/TestExprFromNonZeroFrame.py
@@ -0,0 +1,29 @@
+import lldb
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+
+
+class ExprFromNonZeroFrame(TestBase):
+ NO_DEBUG_INFO_TESTCASE = True
+
+ @skipIf(archs=no_match(["arm64e"]))
+ def test(self):
+ """
+ Tests that we can use SBFrame::EvaluateExpression on a frame
+ that we're not stopped in, even if thread-plans run as part of
+ parsing the expression (e.g., when running static initializers).
+ """
+ self.build()
+
+ (_, _, thread, _) = lldbutil.run_to_source_breakpoint(
+ self, "Break here", lldb.SBFileSpec("main.cpp")
+ )
+ frame = thread.GetFrameAtIndex(1)
+
+ # Using a function pointer inside the expression ensures we
+ # emit a ptrauth static initializer on arm64e into the JITted
+ # expression. The thread-plan that runs for this static
+ # initializer should save/restore the current execution context
+ # frame (which in this test is frame #1).
+ frame.EvaluateExpression("void (*fptr)() = &func; fptr()")
diff --git
a/lldb/test/API/commands/expression/expr-from-non-zero-frame/main.cpp
b/lldb/test/API/commands/expression/expr-from-non-zero-frame/main.cpp
new file mode 100644
index 0000000000000..27105c339f3e5
--- /dev/null
+++ b/lldb/test/API/commands/expression/expr-from-non-zero-frame/main.cpp
@@ -0,0 +1,6 @@
+void func() { __builtin_printf("Break here"); }
+
+int main(int argc) {
+ func();
+ return 0;
+}
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