From 48448cd0c05a0c6ae0926ead8007535ae0658f4e Mon Sep 17 00:00:00 2001 From: Michael Buch Date: Mon, 11 Nov 2024 10:05:54 +0000 Subject: [PATCH] [lldb][ObjC] Fix method list entry offset calculation (#115571) The `relative_list_list_entry_t` offset field in the Objective-C runtime is of type `int64_t`. There are cases where these offsets are negative values. For negative offsets, LLDB would currently incorrectly zero-extend the offset (dropping the fact that the offset was negative), instead producing large offsets that, when added to the `m_baseMethods_ptr` result in addresses that had their upper bits set (e.g., `0x00017ff81b3241b0`). We then would try to `GetMethodList` from such an address but fail to read it (because it's an invalid address). This would manifest in Objective-C decls not getting completed correctly (and formatters not working). We noticed this in CI failures on our Intel bots. This happened to work fine on arm64 because we strip the upper bits when calling `ClassDescriptorV2::method_list_t::Read` using the `FixCodeAddress` ABI plugin API (which doesn't do that on Intel). The fix is to sign-extend the offset calculation. Example failure before this patch: ``` ====================================================================== FAIL: test_break_dwarf (TestRuntimeTypes.RuntimeTypesTestCase) Test setting objc breakpoints using '_regexp-break' and 'breakpoint set'. ---------------------------------------------------------------------- Traceback (most recent call last): File "/Users/michaelbuch/Git/llvm-project/lldb/packages/Python/lldbsuite/test/lldbtest.py", line 1769, in test_method return attrvalue(self) File "/Users/michaelbuch/Git/llvm-project/lldb/test/API/lang/objc/foundation/TestRuntimeTypes.py", line 48, in test_break self.expect( File "/Users/michaelbuch/Git/llvm-project/lldb/packages/Python/lldbsuite/test/lldbtest.py", line 2370, in expect self.runCmd( File "/Users/michaelbuch/Git/llvm-project/lldb/packages/Python/lldbsuite/test/lldbtest.py", line 1000, in runCmd self.assertTrue(self.res.Succeeded(), msg + output) AssertionError: False is not true : Got a valid type Error output: error: :1:11: no known method '+stringWithCString:encoding:'; cast the message send to the method's return type 1 | [NSString stringWithCString:"foo" encoding:1] | ~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Config=x86_64-/Users/michaelbuch/Git/lldb-build-main-no-modules/bin/clang ---------------------------------------------------------------------- ``` (cherry picked from commit 04b295e8938778251821f8a39903fdad0501112c) --- .../ObjC/AppleObjCRuntime/AppleObjCClassDescriptorV2.cpp | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCClassDescriptorV2.cpp b/lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCClassDescriptorV2.cpp index 39969520b7455..54c9f328b5b78 100644 --- a/lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCClassDescriptorV2.cpp +++ b/lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCClassDescriptorV2.cpp @@ -394,7 +394,7 @@ bool ClassDescriptorV2::relative_list_entry_t::Read(Process *process, lldb::offset_t cursor = 0; uint64_t raw_entry = extractor.GetU64_unchecked(&cursor); m_image_index = raw_entry & 0xFFFF; - m_list_offset = (int64_t)(raw_entry >> 16); + m_list_offset = llvm::SignExtend64<48>(raw_entry >> 16); return true; }