llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT--> @llvm/pr-subscribers-lldb Author: Michael Buch (Michael137) <details> <summary>Changes</summary> 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 ``` During 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 after the thread-plan ran (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 --- Full diff: https://github.com/llvm/llvm-project/pull/134097.diff 4 Files Affected: - (modified) lldb/source/Target/Process.cpp (+7-1) - (added) lldb/test/API/commands/expression/expr-from-non-zero-frame/Makefile (+3) - (added) lldb/test/API/commands/expression/expr-from-non-zero-frame/TestExprFromNonZeroFrame.py (+28) - (added) lldb/test/API/commands/expression/expr-from-non-zero-frame/main.cpp (+6) ``````````diff 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..692d24fd2c332 --- /dev/null +++ b/lldb/test/API/commands/expression/expr-from-non-zero-frame/TestExprFromNonZeroFrame.py @@ -0,0 +1,28 @@ +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 + + 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; +} `````````` </details> https://github.com/llvm/llvm-project/pull/134097 _______________________________________________ lldb-commits mailing list lldb-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-commits
