[lldb][DWARF] Don't try to compute address range information of forward declarations

[Michael137]

This fixes the error reported in
#144037.

When computing the aranges table of a CU, LLDB would currently visit all DW_TAG_subprogram DIEs and check their DW_AT_low_pc/DW_AT_high_pc/DW_AT_ranges attributes. If those don't exist it would error out and spam the console. Some subprograms (particularly forward declarations) don't have low/high pc attributes, so it's not really an "error". See DWARFv5 spec section 3.3.3 Subroutine and Entry Point Locations:

A subroutine entry may have either a DW_AT_low_pc and DW_AT_high_pc
pair of attributes or a DW_AT_ranges attribute whose values encode the
contiguous or non-contiguous address ranges, respectively, of the machine
instructions generated for the subroutine (see Section 2.17 on page 51).
...
A subroutine entry representing a subroutine declaration that is not also a
definition does not have code address or range attributes.

We should just ignore those DIEs.

[llvmbot]

@llvm/pr-subscribers-lldb

Author: Michael Buch (Michael137)

Changes

This fixes the error reported in
#144037.

When computing the aranges table of a CU, LLDB would currently visit all DW_TAG_subprogram DIEs and check their DW_AT_low_pc/DW_AT_high_pc. If those don't exist it would error out and spam the console. Some subprograms (particularly forward declarations) don't have low/high pc attributes, so it's not really an "error". We should just ignore those DIEs.

---

Full diff: https://github.com/llvm/llvm-project/pull/144059.diff

2 Files Affected:

• (modified) lldb/source/Plugins/SymbolFile/DWARF/DWARFDebugInfoEntry.cpp (+2-1)
• (added) lldb/test/Shell/SymbolFile/DWARF/forward-declaration-address-ranges.test (+25)

diff --git a/lldb/source/Plugins/SymbolFile/DWARF/DWARFDebugInfoEntry.cpp b/lldb/source/Plugins/SymbolFile/DWARF/DWARFDebugInfoEntry.cpp
index 5196ce89a2c13..d9deffbe7f8b5 100644
--- a/lldb/source/Plugins/SymbolFile/DWARF/DWARFDebugInfoEntry.cpp
+++ b/lldb/source/Plugins/SymbolFile/DWARF/DWARFDebugInfoEntry.cpp
@@ -611,7 +611,8 @@ void DWARFDebugInfoEntry::BuildFunctionAddressRangeTable(
     DWARFUnit *cu, DWARFDebugAranges *debug_aranges) const {
   Log *log = GetLog(DWARFLog::DebugInfo);
   if (m_tag) {
-    if (m_tag == DW_TAG_subprogram) {
+    if (m_tag == DW_TAG_subprogram &&
+        !GetAttributeValueAsOptionalUnsigned(cu, DW_AT_declaration)) {
       if (llvm::Expected<llvm::DWARFAddressRangesVector> ranges =
               GetAttributeAddressRanges(cu, /*check_hi_lo_pc=*/true)) {
         for (const auto &r : *ranges)
diff --git a/lldb/test/Shell/SymbolFile/DWARF/forward-declaration-address-ranges.test b/lldb/test/Shell/SymbolFile/DWARF/forward-declaration-address-ranges.test
new file mode 100644
index 0000000000000..011e2080a8101
--- /dev/null
+++ b/lldb/test/Shell/SymbolFile/DWARF/forward-declaration-address-ranges.test
@@ -0,0 +1,25 @@
+# Test that we don't try to determine address range
+# information of forward declaration DIEs which have
+# no DW_AT_low_pc/DW_AT_high_pc in DWARF.
+
+# RUN: split-file %s %t
+# RUN: %clang_host -c -g -gdwarf %t/main.cpp -o %t.o
+# RUN: %lldb -x -b -s %t/commands.input %t.o -o exit 2>&1 \
+# RUN:       | FileCheck %s
+
+#--- main.cpp
+
+struct Foo {
+  void func() {}
+} foo;
+
+void baz() {
+  foo.func();
+}
+
+#--- commands.input
+
+log enable -v dwarf info
+target modules lookup -n func
+
+# CHECK-NOT: DIE has no address range information

[labath]

Looks good. I don't think the test is very useful. Since all it tests is a negative, the test could be easily invalidated (e.g. by changing the error string), and we would never notice.

You can keep it if you want, but I'd be fine with this even without a test (on the account of us not testing log messages).

[Michael137]

Yea that's fair. I'll remove the test and just add a comment in the source