[lldb] Revive shell test after updating UnwindTable

[jasonmolenda]

In
commit 2f63718
Author: Jason Molenda jmolenda@apple.com
Date: Tue Mar 26 09:07:15 2024 -0700

 [lldb] Don't clear a Module's UnwindTable when adding a SymbolFile (#86603)

I stopped clearing a Module's UnwindTable when we add a SymbolFile to avoid the memory management problems with adding a symbol file asynchronously while the UnwindTable is being accessed on another thread. This broke the target-symbols-add-unwind.test shell test on Linux which removes the DWARF debub_frame section from a binary, loads it, then loads the unstripped binary with the DWARF debug_frame section and checks that the UnwindPlans for a function include debug_frame.

I originally decided that I was willing to sacrifice the possiblity of additional unwind sources from a symbol file because we rely on assembly emulation so heavily, they're rarely critical. But there are targets where we we don't have emluation and rely on things like DWARF debug_frame a lot more, so this probably wasn't a good choice.

This patch adds a new UnwindTable::Update method which looks for any new sources of unwind information and adds it to the UnwindTable, and calls that after a new SymbolFile has been added to a Module.

[llvmbot]

@llvm/pr-subscribers-lldb

Author: Jason Molenda (jasonmolenda)

Changes

In
commit 2f63718
Author: Jason Molenda <jmolenda@apple.com>
Date: Tue Mar 26 09:07:15 2024 -0700

[lldb] Don't clear a Module's UnwindTable when adding a SymbolFile (#<!-- -->86603)

I stopped clearing a Module's UnwindTable when we add a SymbolFile to avoid the memory management problems with adding a symbol file asynchronously while the UnwindTable is being accessed on another thread. This broke the target-symbols-add-unwind.test shell test on Linux which removes the DWARF debub_frame section from a binary, loads it, then loads the unstripped binary with the DWARF debug_frame section and checks that the UnwindPlans for a function include debug_frame.

I originally decided that I was willing to sacrifice the possiblity of additional unwind sources from a symbol file because we rely on assembly emulation so heavily, they're rarely critical. But there are targets where we we don't have emluation and rely on things like DWARF debug_frame a lot more, so this probably wasn't a good choice.

This patch adds a new UnwindTable::Update method which looks for any new sources of unwind information and adds it to the UnwindTable, and calls that after a new SymbolFile has been added to a Module.

---

Full diff: https://github.com/llvm/llvm-project/pull/86770.diff

4 Files Affected:

• (modified) lldb/include/lldb/Symbol/UnwindTable.h (+4)
• (modified) lldb/source/Core/Module.cpp (+2)
• (modified) lldb/source/Symbol/UnwindTable.cpp (+45)
• (added) lldb/test/Shell/SymbolFile/target-symbols-add-unwind.test (+27)

diff --git a/lldb/include/lldb/Symbol/UnwindTable.h b/lldb/include/lldb/Symbol/UnwindTable.h
index f0ce7047de2d1e..26826e5d1b497c 100644
--- a/lldb/include/lldb/Symbol/UnwindTable.h
+++ b/lldb/include/lldb/Symbol/UnwindTable.h
@@ -57,6 +57,10 @@ class UnwindTable {
 
   ArchSpec GetArchitecture();
 
+  /// Called after a SymbolFile has been added to a Module to add any new
+  /// unwind sections that may now be available.
+  void Update();
+
 private:
   void Dump(Stream &s);
 
diff --git a/lldb/source/Core/Module.cpp b/lldb/source/Core/Module.cpp
index a520523a96521a..9c105b3f0e57a1 100644
--- a/lldb/source/Core/Module.cpp
+++ b/lldb/source/Core/Module.cpp
@@ -1009,6 +1009,8 @@ SymbolFile *Module::GetSymbolFile(bool can_create, Stream *feedback_strm) {
         m_symfile_up.reset(
             SymbolVendor::FindPlugin(shared_from_this(), feedback_strm));
         m_did_load_symfile = true;
+        if (m_unwind_table)
+          m_unwind_table->Update();
       }
     }
   }
diff --git a/lldb/source/Symbol/UnwindTable.cpp b/lldb/source/Symbol/UnwindTable.cpp
index 3c1a5187b11054..11bedf3d6052e7 100644
--- a/lldb/source/Symbol/UnwindTable.cpp
+++ b/lldb/source/Symbol/UnwindTable.cpp
@@ -84,6 +84,51 @@ void UnwindTable::Initialize() {
   }
 }
 
+void UnwindTable::Update() {
+  if (!m_initialized)
+    return Initialize();
+
+  std::lock_guard<std::mutex> guard(m_mutex);
+
+  ObjectFile *object_file = m_module.GetObjectFile();
+  if (!object_file)
+    return;
+
+  if (!m_object_file_unwind_up)
+    m_object_file_unwind_up = object_file->CreateCallFrameInfo();
+
+  SectionList *sl = m_module.GetSectionList();
+  if (!sl)
+    return;
+
+  SectionSP sect = sl->FindSectionByType(eSectionTypeEHFrame, true);
+  if (!m_eh_frame_up && sect) {
+    m_eh_frame_up = std::make_unique<DWARFCallFrameInfo>(
+        *object_file, sect, DWARFCallFrameInfo::EH);
+  }
+
+  sect = sl->FindSectionByType(eSectionTypeDWARFDebugFrame, true);
+  if (!m_debug_frame_up && sect) {
+    m_debug_frame_up = std::make_unique<DWARFCallFrameInfo>(
+        *object_file, sect, DWARFCallFrameInfo::DWARF);
+  }
+
+  sect = sl->FindSectionByType(eSectionTypeCompactUnwind, true);
+  if (!m_compact_unwind_up && sect) {
+    m_compact_unwind_up =
+        std::make_unique<CompactUnwindInfo>(*object_file, sect);
+  }
+
+  sect = sl->FindSectionByType(eSectionTypeARMexidx, true);
+  if (!m_arm_unwind_up && sect) {
+    SectionSP sect_extab = sl->FindSectionByType(eSectionTypeARMextab, true);
+    if (sect_extab.get()) {
+      m_arm_unwind_up =
+          std::make_unique<ArmUnwindInfo>(*object_file, sect, sect_extab);
+    }
+  }
+}
+
 UnwindTable::~UnwindTable() = default;
 
 std::optional<AddressRange>
diff --git a/lldb/test/Shell/SymbolFile/target-symbols-add-unwind.test b/lldb/test/Shell/SymbolFile/target-symbols-add-unwind.test
new file mode 100644
index 00000000000000..5420213d405e86
--- /dev/null
+++ b/lldb/test/Shell/SymbolFile/target-symbols-add-unwind.test
@@ -0,0 +1,27 @@
+# TODO: When it's possible to run "image show-unwind" without a running
+# process, we can remove the unsupported line below, and hard-code an ELF
+# triple in the test.
+# UNSUPPORTED: system-windows, system-darwin
+
+# RUN: cd %T
+# RUN: %clang_host %S/Inputs/target-symbols-add-unwind.c -g \
+# RUN:   -fno-unwind-tables -fno-asynchronous-unwind-tables \
+# RUN:   -o target-symbols-add-unwind.debug
+# RUN: llvm-objcopy --strip-debug target-symbols-add-unwind.debug \
+# RUN:   target-symbols-add-unwind.stripped
+# RUN: %lldb target-symbols-add-unwind.stripped -s %s -o quit | FileCheck %s
+
+process launch --stop-at-entry
+image show-unwind -n main
+# CHECK-LABEL: image show-unwind -n main
+# CHECK-NOT: debug_frame UnwindPlan:
+
+target symbols add -s target-symbols-add-unwind.stripped target-symbols-add-unwind.debug
+# CHECK-LABEL: target symbols add
+# CHECK: symbol file {{.*}} has been added to {{.*}}
+
+image show-unwind -n main
+# CHECK-LABEL: image show-unwind -n main
+# CHECK: debug_frame UnwindPlan:
+# CHECK-NEXT: This UnwindPlan originally sourced from DWARF CFI
+# CHECK-NEXT: This UnwindPlan is sourced from the compiler: yes.

[jasonmolenda]

I developed & tested this on aarch64 linux, the only system I have here that runs this shell test. It's a little trickier to test on macOS, we basically only use compact_unwind and it's in the executable binary, not the dSYM SymbolFile.

[JDevlieghere]

Nice!