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When resolving symbols during IR execution, lldb makes a last effort attempt
to resolve external symbols from object files by approximate name matching.
It currently uses `CPlusPlusNameParser` to parse the demangled function name
and arguments for the unresolved symbol and its candidates. However, this
hand-rolled C++ parser doesn’t support ABI tags which, depending on the
demangler,
get demangled into `[abi:tag]`. This lack of parsing support causes lldb to
never
consider a candidate mangled function name that has ABI tags.
The issue reproduces by calling an ABI-tagged template function from the
expression evaluator. This is particularly problematic with the recent
addition of ABI tags to numerous libcxx APIs.
The issue stems from the fact that `clang::CodeGen` emits function
function calls using the mangled name inferred from the `FunctionDecl`
LLDB constructs from DWARF. Debug info often lacks information for
us to construct a perfect FunctionDecl resulting in subtle mangled
name inaccuracies.
This patch side-steps the problem of inaccurate `FunctionDecl`s by
attaching an `asm()` label to each `FunctionDecl` LLDB creates from DWARF.
`clang::CodeGen` consults this label to get the mangled name as one of
the first courses of action when emitting a function call.
LLDB already does this for C++ member functions as of
675767a5910d2ec77ef8b51c78fe312cf9022896 <https://reviews.llvm.org/D40283>
**Testing**
- Added API tests
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D131974
Files:
lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp
lldb/test/API/lang/cpp/abi_tag_lookup/Makefile
lldb/test/API/lang/cpp/abi_tag_lookup/TestAbiTagLookup.py
lldb/test/API/lang/cpp/abi_tag_lookup/main.cpp
Index: lldb/test/API/lang/cpp/abi_tag_lookup/main.cpp
===================================================================
--- /dev/null
+++ lldb/test/API/lang/cpp/abi_tag_lookup/main.cpp
@@ -0,0 +1,71 @@
+#include <cstdio>
+
+namespace A {
+template <typename T> bool operator<(const T &, const T &) { return true; }
+
+template <typename T>
+[[gnu::abi_tag("Two", "Tags")]] bool operator>(const T &, const T &) {
+ return true;
+}
+
+template <typename T>
+[[gnu::abi_tag("OneTag")]] bool operator==(const T &, const T &) {
+ return true;
+}
+
+[[gnu::abi_tag("Foo")]] int withAbiTagInNS(const int &, const int &) {
+ return 1;
+}
+
+template <typename T>
+[[gnu::abi_tag("Bar")]] int withAbiTagInNS(const T &, const T &) {
+ return 2;
+}
+
+struct B {};
+} // namespace A
+
+template <typename T>
+[[gnu::abi_tag("Baz")]] int withAbiTag(const T &, const T &) {
+ return 3;
+}
+
+[[gnu::abi_tag("Baz")]] int withAbiTag(const int &, const int &) { return -3; }
+
+struct Simple {
+ int mem;
+};
+
+struct [[gnu::abi_tag("Qux")]] Tagged {
+ int mem;
+
+ int const &Value() const { return mem; }
+};
+
+template <typename T> struct [[gnu::abi_tag("Quux", "Quuux")]] TaggedTemplate {
+ T mem;
+
+ T const &Value() const { return mem; }
+};
+
+// clang-format off
+inline namespace [[gnu::abi_tag("Inline", "NS")]] v1 {
+template <typename T> int withImplicitTag(T const &t) { return t.mem; }
+} // namespace
+// clang-format on
+
+int main() {
+ A::B b1;
+ A::B b2;
+ Tagged t{.mem = 4};
+ TaggedTemplate<int> tt{.mem = 5};
+
+ int result = (b1 < b2) + (b1 > b2) + (b1 == b2) + withAbiTag(b1, b2) +
+ A::withAbiTagInNS(1.0, 2.0) + withAbiTagInNS(b1, b2) +
+ A::withAbiTagInNS(1, 2) + withImplicitTag(Tagged{.mem = 6}) +
+ withImplicitTag(Simple{.mem = 6}) + t.Value() + tt.Value();
+
+ std::puts("Break here");
+
+ return result;
+}
Index: lldb/test/API/lang/cpp/abi_tag_lookup/TestAbiTagLookup.py
===================================================================
--- /dev/null
+++ lldb/test/API/lang/cpp/abi_tag_lookup/TestAbiTagLookup.py
@@ -0,0 +1,52 @@
+"""
+Test that we can call functions and use types
+annotated (and thus mangled) with ABI tags.
+"""
+
+import lldb
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+
+class AbiTagLookupTestCase(TestBase):
+
+ @skipIfWindows
+ @expectedFailureAll(debug_info=["dwarf", "gmodules", "dwo"])
+ def test_abi_tag_lookup(self):
+ self.build()
+ lldbutil.run_to_source_breakpoint(self, 'Break here',
+ lldb.SBFileSpec("main.cpp", False))
+
+ # Qualified/unqualified lookup to templates in namespace
+ self.expect_expr("operator<(b1, b2)", result_type="bool", result_value="true")
+ self.expect_expr("A::operator<(b1, b2)", result_type="bool", result_value="true")
+ self.expect_expr("b1 < b2", result_type="bool", result_value="true")
+
+ # Qualified/unqualified lookup to templates with ABI tags in namespace
+ self.expect_expr("operator>(b1, b2)", result_type="bool", result_value="true")
+ self.expect_expr("A::operator>(b1, b2)", result_type="bool", result_value="true")
+ self.expect_expr("b1 > b2", result_type="bool", result_value="true")
+
+ # Call non-operator templates with ABI tags
+ self.expect_expr("A::withAbiTagInNS(1, 1)", result_type="int", result_value="1")
+
+ self.expect_expr("A::withAbiTagInNS(1.0, 1.0)", result_type="int", result_value="2")
+ self.expect_expr("withAbiTagInNS(b1, b2)", result_type="int", result_value="2")
+ self.expect_expr("A::withAbiTagInNS(b1, b2)", result_type="int", result_value="2")
+
+ self.expect_expr("withAbiTag(b1, b2)", result_type="int", result_value="3")
+ self.expect_expr("withAbiTag(0, 0)", result_type="int", result_value="-3")
+
+ # Structures with ABI tags
+ self.expect_expr("t.Value()", result_type="const int", result_value="4")
+ self.expect_expr("tt.Value()", result_type="const int", result_value="5")
+
+ self.expect_expr("Tagged{.mem = 6}", result_type="Tagged",
+ result_children=[ValueCheck(name="mem", value="6")])
+
+ # Inline namespaces with ABI tags
+ self.expect_expr("v1::withImplicitTag(Simple{.mem = 6})", result_type="int", result_value="6")
+ self.expect_expr("withImplicitTag(Simple{.mem = 6})", result_type="int", result_value="6")
+
+ self.expect_expr("v1::withImplicitTag(Tagged{.mem = 6})", result_type="int", result_value="6")
+ self.expect_expr("withImplicitTag(Tagged{.mem = 6})", result_type="int", result_value="6")
Index: lldb/test/API/lang/cpp/abi_tag_lookup/Makefile
===================================================================
--- /dev/null
+++ lldb/test/API/lang/cpp/abi_tag_lookup/Makefile
@@ -0,0 +1,3 @@
+CXX_SOURCES := main.cpp
+
+include Makefile.rules
Index: lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp
===================================================================
--- lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp
+++ lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp
@@ -1248,6 +1248,17 @@
lldbassert(function_decl);
if (function_decl) {
+ // Attach an asm(<mangled_name>) label to the FunctionDecl
+ // This ensures that clang::CodeGen emits function calls
+ // using symbols that are mangled according to the DW_AT_linkage_name.
+ // If we didn't do this the external symbols wouldn't exactly
+ // match the mangled name LLDB knows about and the IRExecutionUnit
+ // would have to fall back to searching object files for
+ // approximately matching function names. The motivating
+ // example is generating calls to ABI-tagged template functions.
+ function_decl->addAttr(clang::AsmLabelAttr::CreateImplicit(
+ m_ast.getASTContext(), attrs.mangled_name, /*literal=*/false));
+
LinkDeclContextToDIE(function_decl, die);
if (!function_param_decls.empty()) {
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