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

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Oct 24, 2023
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[Reland] Detect against invalid variant index for LibStdC++ std::variant data formatters #69614

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5 changes: 5 additions & 0 deletions lldb/examples/synthetic/gnu_libstdcpp.py
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Original file line number Diff line number Diff line change
Expand Up @@ -914,6 +914,11 @@ def get_variant_npos_value(index_byte_size):
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()} "

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3 changes: 2 additions & 1 deletion lldb/source/Plugins/TypeSystem/Clang/TypeSystemClang.cpp
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Expand Up @@ -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;
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Is this change needed now that the formatter is checking the number of arguments up front?

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It is requested by @clayborg's comment in the original patch:

If this is what was crashing, we should modify the GetTemplateArgumentType() to not crash with an inalid index as part of this fix.

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+1, we should still include this change. We shouldn't crash if the idx argument is too high.

return &pack.pack_elements()[pack_idx];
}

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26 changes: 26 additions & 0 deletions .../data-formatter/data-formatter-stl/libstdcpp/variant/TestDataFormatterLibStdcxxVariant.py
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Expand Up @@ -71,3 +71,29 @@ def test_with_run_command(self):
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>"])