Unverified Commit 00d3ed6d authored by jeffreytan81's avatar jeffreytan81 Committed by GitHub
Browse files

[Reland] Detect against invalid variant index for LibStdC++ std::variant data formatters (#69614) 

This is relanding of https://github.com/llvm/llvm-project/pull/69253.
`TestTemplatePackArgs.py` is passing now.

https://github.com/llvm/llvm-project/pull/68012/files

 added new data
formatters for LibStdC++ std::variant.

However, this formatter can crash if std::variant's index field has
invalid value (exceeds the number of template arguments).
This can happen if the current IP stops at a place std::variant is not
initialized yet.

This patch fixes the crash by ensuring the index is a valid value and
fix GetNthTemplateArgument() to make sure it is not crashing.

Co-authored-by: default avatarjeffreytan81 <jeffreytan@fb.com>
parent ec064593

lldb/examples/synthetic/gnu_libstdcpp.py

+5 −0
Original line number Diff line number Diff line
@@ -914,6 +914,11 @@ def VariantSummaryProvider(valobj, dict): 
    if index == npos_value:

        return " No Value"



    # Invalid index can happen when the variant is not initialized yet.

    template_arg_count = data_obj.GetType().GetNumberOfTemplateArguments()

    if index >= template_arg_count:

        return " <Invalid>"



    active_type = data_obj.GetType().GetTemplateArgumentType(index)

    return f" Active Type = {active_type.GetDisplayTypeName()} "

lldb/source/Plugins/TypeSystem/Clang/TypeSystemClang.cpp

+2 −1
Original line number Diff line number Diff line
@@ -7183,7 +7183,8 @@ GetNthTemplateArgument(const clang::ClassTemplateSpecializationDecl *decl, 
  // (including the ones preceding the parameter pack).

  const auto &pack = args[last_idx];

  const size_t pack_idx = idx - last_idx;

  assert(pack_idx < pack.pack_size() && "parameter pack index out-of-bounds");

  if (pack_idx >= pack.pack_size())

    return nullptr;

  return &pack.pack_elements()[pack_idx];

}

lldb/test/API/functionalities/data-formatter/data-formatter-stl/libstdcpp/variant/TestDataFormatterLibStdcxxVariant.py

+26 −0
Original line number Diff line number Diff line
@@ -71,3 +71,29 @@ class LibStdcxxVariantDataFormatterTestCase(TestBase): 
            substrs=["v_many_types_no_value =  No Value"],

        )

        """



    @add_test_categories(["libstdcxx"])

    def test_invalid_variant_index(self):

        """Test LibStdC++ data formatter for std::variant with invalid index."""

        self.build()



        (self.target, self.process, thread, bkpt) = lldbutil.run_to_source_breakpoint(

            self, "// break here", lldb.SBFileSpec("main.cpp", False)

        )



        lldbutil.continue_to_breakpoint(self.process, bkpt)



        self.expect(

            "frame variable v1",

            substrs=["v1 =  Active Type = int  {", "Value = 12", "}"],

        )



        var_v1 = thread.frames[0].FindVariable("v1")

        var_v1_raw_obj = var_v1.GetNonSyntheticValue()

        index_obj = var_v1_raw_obj.GetChildMemberWithName("_M_index")

        self.assertTrue(index_obj and index_obj.IsValid())



        INVALID_INDEX = "100"

        index_obj.SetValueFromCString(INVALID_INDEX)



        self.expect("frame variable v1", substrs=["v1 =  <Invalid>"])