[LLDB] Hide unresolvable children from ObjC tagged pointers (#211936)
Foundation's small value inline representations have valid summaries and sometimed synthetic children, but LLDB cannot access any ivars from their base classes (such as [NSObject isa]). Use a synthetic child provider to hide them. rdar://182434208 Assisted-by: claude
This commit is contained in:
Adrian Prantl
GitHub
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8 changed files with 231 additions and 0 deletions
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@ -881,6 +881,45 @@ lldb::TypeCategoryImplSP ObjCLanguage::GetFormatters() {
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return g_category;
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}
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HardcodedFormatters::HardcodedSyntheticFinder
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ObjCLanguage::GetHardcodedSynthetics() {
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static llvm::once_flag g_initialize;
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static HardcodedFormatters::HardcodedSyntheticFinder g_formatters;
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llvm::call_once(g_initialize, []() -> void {
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// An Objective-C tagged pointer (e.g. a single-index NSIndexSet
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// or a small NSNumber) packs its whole state into the pointer
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// bits and has no object in memory. Since its declared base
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// classes and ivars cannot be read, this synthtic child provider
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// hides them. Other synthetic child providers take precedence of
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// this.
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g_formatters.push_back(
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[](lldb_private::ValueObject &valobj, lldb::DynamicValueType,
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FormatManager &) -> SyntheticChildren::SharedPointer {
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static CXXSyntheticChildren::SharedPointer formatter_sp(
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new CXXSyntheticChildren(
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SyntheticChildren::Flags()
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.SetCascades(true)
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.SetSkipPointers(false)
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.SetSkipReferences(false)
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.SetNonCacheable(true),
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"tagged pointer synthetic children",
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lldb_private::formatters::ObjCClassSyntheticFrontEndCreator));
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ProcessSP process_sp = valobj.GetProcessSP();
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if (!process_sp)
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return nullptr;
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if (ObjCLanguageRuntime *runtime =
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ObjCLanguageRuntime::Get(*process_sp))
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if (runtime->IsTaggedPointerValue(valobj))
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return formatter_sp;
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return nullptr;
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});
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});
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return g_formatters;
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}
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std::vector<FormattersMatchCandidate>
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ObjCLanguage::GetPossibleFormattersMatches(ValueObject &valobj,
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lldb::DynamicValueType use_dynamic) {
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@ -146,6 +146,9 @@ public:
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lldb::TypeCategoryImplSP GetFormatters() override;
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HardcodedFormatters::HardcodedSyntheticFinder
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GetHardcodedSynthetics() override;
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std::vector<FormattersMatchCandidate>
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GetPossibleFormattersMatches(ValueObject &valobj,
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lldb::DynamicValueType use_dynamic) override;
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@ -290,6 +290,23 @@ ObjCLanguageRuntime::GetClassDescriptor(ValueObject &valobj) {
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return objc_class_sp;
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}
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bool ObjCLanguageRuntime::IsTaggedPointerValue(ValueObject &in_value) {
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TaggedPointerVendor *tagged_pointer_vendor = GetTaggedPointerVendor();
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if (!tagged_pointer_vendor)
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return false;
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// Only Objective-C object values can be tagged pointers.
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if (!(in_value.GetTypeInfo() & lldb::eTypeIsObjC))
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return false;
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addr_t ptr = in_value.IsPointerType() ? in_value.GetPointerValue().address
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: in_value.GetAddressOf().address;
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if (ptr == LLDB_INVALID_ADDRESS)
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return false;
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return tagged_pointer_vendor->IsPossibleTaggedPointer(ptr);
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}
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ObjCLanguageRuntime::ClassDescriptorSP
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ObjCLanguageRuntime::GetNonKVOClassDescriptor(ValueObject &valobj) {
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ObjCLanguageRuntime::ClassDescriptorSP objc_class_sp(
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@ -233,6 +233,8 @@ public:
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virtual TaggedPointerVendor *GetTaggedPointerVendor() { return nullptr; }
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bool IsTaggedPointerValue(ValueObject &in_value);
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typedef std::shared_ptr<EncodingToType> EncodingToTypeSP;
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virtual EncodingToTypeSP GetEncodingToType();
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4
lldb/test/API/lang/objc/tagged-pointer-children/Makefile
Normal file
4
lldb/test/API/lang/objc/tagged-pointer-children/Makefile
Normal file
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@ -0,0 +1,4 @@
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OBJC_SOURCES := main.m
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LD_EXTRAS := -lobjc -framework Foundation
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include Makefile.rules
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@ -0,0 +1,115 @@
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import lldb
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from lldbsuite.test.decorators import *
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from lldbsuite.test.lldbtest import *
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from lldbsuite.test import lldbutil
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class TaggedPointerChildrenTestCase(TestBase):
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def is_tagged(self, valobj):
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"""Return True if valobj holds an Objective-C tagged pointer."""
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res = lldb.SBCommandReturnObject()
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ci = self.dbg.GetCommandInterpreter()
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ci.HandleCommand(
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"language objc tagged-pointer info %s" % valobj.GetValue(), res
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)
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return res.Succeeded() and "is tagged" in res.GetOutput()
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def assert_no_unreadable_children(self, valobj):
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"""Recursively assert no child of valobj fails with a memory-read error."""
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for i in range(valobj.GetNumChildren()):
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child = valobj.GetChildAtIndex(i)
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err = child.GetError()
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self.assertFalse(
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err.Fail() and "read memory" in (err.GetCString() or ""),
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"child '%s' of '%s' has a memory-read error: %s"
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% (child.GetName(), valobj.GetName(), err.GetCString()),
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)
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self.assert_no_unreadable_children(child)
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@skipUnlessDarwin
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@skipIf(archs=["i386", "i686"])
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def test(self):
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"""
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Test that Objective-C tagged pointers (inline values) do not present phantom,
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memory-backed children.
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"""
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self.build()
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_, _, thread, _ = lldbutil.run_to_source_breakpoint(
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self, "// break here", lldb.SBFileSpec("main.m")
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)
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frame = thread.GetSelectedFrame()
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tagged = frame.FindVariable("tagged")
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self.assertTrue(tagged.IsValid(), "found 'tagged'")
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# If this platform does not represent a single-index NSIndexSet as a
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# tagged pointer there is nothing to test.
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if not self.is_tagged(tagged):
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self.skipTest("NSIndexSet is not a tagged pointer on this platform")
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# The tagged pointer is still summarized.
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self.assertIsNotNone(tagged.GetSummary())
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self.assertIn("index", tagged.GetSummary())
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# But it must not present any unresolvable children.
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self.assertEqual(
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tagged.GetNumChildren(),
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0,
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"tagged pointer must not have children",
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)
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self.assertFalse(tagged.MightHaveChildren())
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self.assert_no_unreadable_children(tagged)
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# Sanity check.
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heap = frame.FindVariable("heap")
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self.assertTrue(heap.IsValid(), "found 'heap'")
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self.assertFalse(self.is_tagged(heap), "'heap' is a real object")
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self.assertGreater(heap.GetNumChildren(), 0, "real object still has children")
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self.assert_no_unreadable_children(heap)
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@skipUnlessDarwin
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@skipIf(archs=["i386", "i686"])
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def test_registered_synthetic_takes_precedence(self):
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"""
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A synthetic child provider registered for the type must still fire for
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a tagged pointer. ObjCLanguage's hardcoded "no children" provider is
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only a fallback and must be consulted after any registered synthetic.
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"""
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self.build()
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_, _, thread, _ = lldbutil.run_to_source_breakpoint(
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self, "// break here", lldb.SBFileSpec("main.m")
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)
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frame = thread.GetSelectedFrame()
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tagged = frame.FindVariable("tagged")
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self.assertTrue(tagged.IsValid(), "found 'tagged'")
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if not self.is_tagged(tagged):
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self.skipTest("NSIndexSet is not a tagged pointer on this platform")
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# Without a registered synthetic, the hardcoded fallback reports no
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# children for the tagged pointer.
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self.assertEqual(tagged.GetNumChildren(), 0)
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# Register a synthetic child provider for NSIndexSet.
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import os
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provider = os.path.join(os.path.dirname(__file__), "tagged_synth_provider.py")
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self.runCmd("command script import " + provider)
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self.runCmd(
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'type synthetic add -x "NSIndexSet" '
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"-l tagged_synth_provider.TaggedSyntheticProvider"
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)
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self.addTearDownHook(lambda: self.runCmd("type synthetic clear", check=False))
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# The registered provider must now win over the hardcoded fallback.
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tagged = frame.FindVariable("tagged")
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self.assertEqual(
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tagged.GetNumChildren(),
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1,
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"registered synthetic must take precedence over the hardcoded "
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"tagged-pointer fallback",
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)
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self.assertTrue(tagged.MightHaveChildren())
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child = tagged.GetChildAtIndex(0)
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self.assertEqual(child.GetName(), "synthetic_child")
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self.assertEqual(child.GetValueAsSigned(), 42)
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19
lldb/test/API/lang/objc/tagged-pointer-children/main.m
Normal file
19
lldb/test/API/lang/objc/tagged-pointer-children/main.m
Normal file
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@ -0,0 +1,19 @@
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#import <Foundation/Foundation.h>
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int main(int argc, const char *argv[]) {
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@autoreleasepool {
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// A single-index NSIndexSet is stored as an Objective-C tagged pointer.
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// It has a summary but no ivars or base classes LLDB could materialize
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// from memory.
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NSIndexSet *tagged = [NSIndexSet indexSetWithIndex:1];
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// A discontiguous set cannot be tagged, so it is a real heap object with a
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// readable isa and ivar layout.
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NSMutableIndexSet *heap = [NSMutableIndexSet indexSet];
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[heap addIndex:1];
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[heap addIndex:1000000];
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NSLog(@"%@ %@", tagged, heap); // break here
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}
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return 0;
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}
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@ -0,0 +1,32 @@
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import lldb
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class TaggedSyntheticProvider:
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"""A custom synthetic child provider that produces a single child that
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does not depend on reading the tagged pointer's (nonexistent) backing
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memory, so it works for tagged pointers.
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"""
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def __init__(self, valobj, internal_dict):
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self.valobj = valobj
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def num_children(self):
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return 1
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def get_child_index(self, name):
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return 0 if name == "synthetic_child" else -1
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def get_child_at_index(self, index):
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if index != 0:
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return lldb.SBValue()
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# Build the child from raw data rather than by reading the object, so it
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# works for a tagged pointer (which has no backing memory).
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target = self.valobj.GetTarget()
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int_type = target.GetBasicType(lldb.eBasicTypeInt)
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data = lldb.SBData.CreateDataFromSInt32Array(
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target.GetByteOrder(), target.GetAddressByteSize(), [42]
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)
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return self.valobj.CreateValueFromData("synthetic_child", data, int_type)
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def update(self):
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return False
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