[lldb][test] Add test-cases for packed/aligned structures

[Michael137]

Adds test that checks whether LLDB correctly infers the
alignment of packed structures. Specifically, the
InferAlignment code-path of the ItaniumRecordLayoutBuilder
where it assumes that overlapping field offsets imply a
packed structure and thus sets alignment to 1. See discussion
in #93809.

While here, also added a test-case where we check alignment of
a class whose base has an explicit `DW_AT_alignment
(those don't get transitively propagated in DWARF, but don't seem
like a problem for LLDB).

Lastly, also added an XFAIL-ed tests where the aforementioned
InferAlignment kicks in for overlapping fields (but in this
case incorrectly since the structure isn't actually packed).

[llvmbot]

@llvm/pr-subscribers-lldb

Author: Michael Buch (Michael137)

Changes

Adds test that checks that LLDB correctly infers the alignment of packed structures. Specifically, the
InferAlignment code-path of the ItaniumRecordLayoutBuilder where it assumes that overlapping field offsets imply a packed structure and thus sets alignment to 1. See discussion in #93809.

Also adds two XFAIL-ed tests:

1. where LLDB doesn't correctly infer the alignment of a derived class whose base has an explicit `DW_AT_alignment. See DebugInfo: No alignment info for "transitive" alignment-enforced structures. #73623.
2. where the aforementioned InferAlignment kicks in for overlapping fields (but in this case incorrectly since the structure isn't actually packed).

---

Full diff: https://github.com/llvm/llvm-project/pull/96932.diff

4 Files Affected:

• (modified) lldb/test/API/lang/cpp/alignas_base_class/TestAlignAsBaseClass.py (+8)
• (modified) lldb/test/API/lang/cpp/alignas_base_class/main.cpp (+6)
• (added) lldb/test/Shell/SymbolFile/DWARF/no_unique_address-alignment.cpp (+25)
• (added) lldb/test/Shell/SymbolFile/DWARF/packed.cpp (+36)

diff --git a/lldb/test/API/lang/cpp/alignas_base_class/TestAlignAsBaseClass.py b/lldb/test/API/lang/cpp/alignas_base_class/TestAlignAsBaseClass.py
index 7d97b0c42b7e1..f9c99d15e5891 100644
--- a/lldb/test/API/lang/cpp/alignas_base_class/TestAlignAsBaseClass.py
+++ b/lldb/test/API/lang/cpp/alignas_base_class/TestAlignAsBaseClass.py
@@ -16,3 +16,11 @@ def test(self):
         # Verify specified class alignments.
         self.expect_expr("alignof(B2)", result_value="8")
         self.expect_expr("alignof(EmptyClassAlign8)", result_value="8")
+
+    @no_debug_info_test
+    @expectedFailureAll(bugnumber="https://github.com/llvm/llvm-project/issues/73623")
+    def test(self):
+        self.build()
+        self.dbg.CreateTarget(self.getBuildArtifact("a.out"))
+
+        self.expect_expr("alignof(Derived)", result_value="8")
diff --git a/lldb/test/API/lang/cpp/alignas_base_class/main.cpp b/lldb/test/API/lang/cpp/alignas_base_class/main.cpp
index 9d37554957ba3..fb922c42edfc3 100644
--- a/lldb/test/API/lang/cpp/alignas_base_class/main.cpp
+++ b/lldb/test/API/lang/cpp/alignas_base_class/main.cpp
@@ -13,4 +13,10 @@ D d3g;
 struct alignas(8) EmptyClassAlign8 {
 } t;
 
+struct alignas(8) __attribute__((packed)) AlignedAndPackedBase {} foo;
+
+struct Derived : AlignedAndPackedBase {
+} bar;
+static_assert(alignof(Derived) == 8);
+
 int main() {}
diff --git a/lldb/test/Shell/SymbolFile/DWARF/no_unique_address-alignment.cpp b/lldb/test/Shell/SymbolFile/DWARF/no_unique_address-alignment.cpp
new file mode 100644
index 0000000000000..79199a9237a63
--- /dev/null
+++ b/lldb/test/Shell/SymbolFile/DWARF/no_unique_address-alignment.cpp
@@ -0,0 +1,25 @@
+// XFAIL: *
+
+// RUN: %clangxx_host -gdwarf -o %t %s
+// RUN: %lldb %t \
+// RUN:   -o "b main" \
+// RUN:   -o "expr alignof(OverlappingFields)" \
+// RUN:   -o "expr sizeof(OverlappingFields)" \
+// RUN:   -o exit | FileCheck %s
+
+// CHECK:      (lldb) expr alignof(OverlappingFields)
+// CHECK-NEXT: ${{.*}} = 4
+// CHECK:      (lldb) expr sizeof(OverlappingFields)
+// CHECK-NEXT: ${{.*}} = 8
+
+struct Empty {};
+
+struct OverlappingFields {
+    char y;
+    [[no_unique_address]] Empty e;
+    int z;
+} g_packed_struct;
+static_assert(alignof(OverlappingFields) == 4);
+static_assert(sizeof(OverlappingFields) == 8);
+
+int main() {}
diff --git a/lldb/test/Shell/SymbolFile/DWARF/packed.cpp b/lldb/test/Shell/SymbolFile/DWARF/packed.cpp
new file mode 100644
index 0000000000000..53b5ee624472c
--- /dev/null
+++ b/lldb/test/Shell/SymbolFile/DWARF/packed.cpp
@@ -0,0 +1,36 @@
+// RUN: %clangxx_host -gdwarf -o %t %s
+// RUN: %lldb %t \
+// RUN:   -o "b main" \
+// RUN:   -o "expr alignof(packed)" \
+// RUN:   -o "expr sizeof(packed)" \
+// RUN:   -o "expr alignof(packed_and_aligned)" \
+// RUN:   -o "expr sizeof(packed_and_aligned)" \
+// RUN:   -o exit | FileCheck %s
+
+// CHECK:      (lldb) expr alignof(packed)
+// CHECK-NEXT: ${{.*}} = 1
+// CHECK:      (lldb) expr sizeof(packed)
+// CHECK-NEXT: ${{.*}} = 9
+
+// CHECK:      (lldb) expr alignof(packed_and_aligned)
+// CHECK-NEXT: ${{.*}} = 16
+// CHECK:      (lldb) expr sizeof(packed_and_aligned)
+// CHECK-NEXT: ${{.*}} = 16
+
+struct __attribute__((packed)) packed {
+    int x;
+    char y;
+    int z;
+} g_packed_struct;
+static_assert(alignof(packed) == 1);
+static_assert(sizeof(packed) == 9);
+
+struct __attribute__((packed, aligned(16))) packed_and_aligned {
+    int x;
+    char y;
+    int z;
+} g_packed_and_aligned_struct;
+static_assert(alignof(packed_and_aligned) == 16);
+static_assert(sizeof(packed_and_aligned) == 16);
+
+int main() {}

[labath]

It looks like you're not actually running the binary. Do you need the breakpoint?

[Michael137]

good catch, removed

[labath]

same here