[LLDB] - Fix setting the breakpoints when -gsplit-dwarf and DWARF 5 were used for building the executable.

[grimar]

Summary

Imagine the following code:

void baz() {
}

int main() {
  baz();
  return 0;
}

When compiling with with -gdwarf-4 -gsplit-dwarf LLDB is able to set the breakpoint correctly:

clang test.cc -g -fno-rtti -c -gdwarf-4 -gsplit-dwarf
clang test.o -g -fno-rtti -gdwarf-4 -o test -gsplit-dwarf
lldb test
(lldb) target create "test"
Current executable set to 'test' (x86_64).
(lldb) b baz
Breakpoint 1: where = test`baz() + 4 at test.cc:4:1, address = 0x0000000000400524

But not when -dwarf-5 is used. It thinks there are 2 locations:

clang test.cc -g -fno-rtti -c -gdwarf-5 -gsplit-dwarf
clang test.o -g -fno-rtti -gdwarf-5 -o test -gsplit-dwarf
lldb test
(lldb) target create "test"
Current executable set to 'test' (x86_64).
(lldb) b baz
Breakpoint 1: 2 locations.

The issue happens because starting from DWARF v5 DW_AT_addr_base attribute should be used
instead of DW_AT_GNU_addr_base. LLDB does not do that and we end up reading the
.debug_addr header as section content (as addresses) instead of skipping it and reading the real addresses.
Then LLDB is unable to match 2 similar locations and thinks they are different.

[grimar]

• Added the test case forgotten.

[jankratochvil]

I do not think my approval is sufficient but I agree with the patch.

[jankratochvil]

source/Plugins/SymbolFile/DWARF/DWARFUnit.cpp

352

Here I would find good also a comment:

// pre-DWARF v5 attributes DW_AT_GNU_* applied only to the DWO unit while DWARF v5 attributes DW_AT_* apply also to the main unit

Based on a DebugFission comment:

Note the following difference between the current GCC implementation and the DWARF v5 specification: In the current GCC implementation (based on DWARF v4), if DW_AT_ranges is present, the offset into the ranges table is not relative to the value given by DW_AT_ranges_base (i.e., DW_AT_ranges_base is used only for references to the range table from the dwo sections). In DWARF v5, the DW_AT_ranges_base attribute is used for all references to the range table -- both from dwo sections and from skeleton compile units.

I was also thinking to fetch the attributes just once by some (m_version >= 5 ? DW_AT_addr_base : DW_AT_GNU_addr_base) but clang-7.0 does produce DWARF-5 still using DW_AT_GNU_addr_base.

[grimar]

Thanks for looking at this, Jan!

• Rewrote the comment.

source/Plugins/SymbolFile/DWARF/DWARFUnit.cpp

352

I rewrote the comment.

I was also thinking to fetch the attributes just once by some (m_version >= 5 ? DW_AT_addr_base : DW_AT_GNU_addr_base) but clang-7.0 does produce DWARF-5 still using DW_AT_GNU_addr_base.

Yeah, it would not be safe to do such check I think. But it should not be an issue, in practice, I believe it should be fine to check both the attributes in order.

[clayborg]

See inlined comments.

source/Plugins/SymbolFile/DWARF/DWARFUnit.cpp

354

if (addr_base == LLDB_INVALID_ADDRESS)

[clayborg]

Missed an inline comment on last comment

source/Plugins/SymbolFile/DWARF/DWARFUnit.cpp

311

Use LLDB_INVALID_ADDRESS instead of zero as zero could be a valid base address.

dw_addr_t addr_base = cu_die.GetAttributeValueAsUnsigned(m_dwarf, this, DW_AT_addr_base, LLDB_INVALID_ADDRESS);

355–356

addr_base = cu_die.GetAttributeValueAsUnsigned(m_dwarf, this, DW_AT_GNU_addr_base, LLDB_INVALID_ADDRESS);

[grimar]

• Addressed review comments.

[clayborg]

source/Plugins/SymbolFile/DWARF/DWARFUnit.cpp

355–356

Do we still want the addr_base to default to zero instead of LLDB_INVALID_ADDRESS here?

[grimar]

source/Plugins/SymbolFile/DWARF/DWARFUnit.cpp

355–356

I believe so. Setting the addr_base to default zero looks fine to me. That way the existent code does not
need to check for LLDB_INVALID_ADDRESS and can just call the GetAddrBase and add the result
to the offset calculation.
That is how things already work and I do not see any benefits from changing this behavior probably?

[clayborg]

source/Plugins/SymbolFile/DWARF/DWARFUnit.cpp

355–356

Sounds good, just wanted to check.

lit/Breakpoint/Inputs/split-dwarf-5-addrbase.dwo.yaml

+--- !ELF
+FileHeader:      
+  Class:           ELFCLASS64
+  Data:            ELFDATA2LSB
+  Type:            ET_REL
+  Machine:         EM_X86_64
+Sections:        
+  - Name:            .debug_loc.dwo
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_EXCLUDE ]
+    AddressAlign:    0x0000000000000001
+    Content:         ''
+  - Name:            .debug_str_offsets.dwo
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_EXCLUDE ]
+    AddressAlign:    0x0000000000000001
+    Content:         200000000500000000000000090000002C000000340000003C0000004000000045000000
+  - Name:            .debug_str.dwo
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_EXCLUDE, SHF_MERGE, SHF_STRINGS ]
+    AddressAlign:    0x0000000000000001
+    Content:         746573742E64776F00636C616E672076657273696F6E20382E302E3020287472756E6B203334373239392900746573742E6363005F5A3362617A760062617A006D61696E00696E7400
+  - Name:            .debug_info.dwo
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_EXCLUDE ]
+    AddressAlign:    0x0000000000000001
+    Content:         360000000500050800000000E93484C441B7E84A01000104000202000600000001560304010103011C0000000156050104350000000406050400
+  - Name:            .debug_abbrev.dwo
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_EXCLUDE ]
+    AddressAlign:    0x0000000000000001
+    Content:         011101B042252525130503250000022E00111B120640186E2503253A0B3B0B3F190000032E00111B1206401803253A0B3B0B49133F19000004240003253E0B0B0B000000
+Symbols:         {}
+DynamicSymbols:  {}
+...

lit/Breakpoint/Inputs/split-dwarf-5-addrbase.yaml

+--- !ELF
+FileHeader:      
+  Class:           ELFCLASS64
+  Data:            ELFDATA2LSB
+  Type:            ET_EXEC
+  Machine:         EM_X86_64
+  Entry:           0x0000000000400440
+Sections:
+  - Name:            .text
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC, SHF_EXECINSTR ]
+    Address:         0x0000000000400440
+    AddressAlign:    0x0000000000000010
+    Content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
+  - Name:            .debug_str_offsets
+    Type:            SHT_PROGBITS
+    AddressAlign:    0x0000000000000001
+    Content:         0C000000050000000000000009000000
+  - Name:            .debug_str
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_MERGE, SHF_STRINGS ]
+    AddressAlign:    0x0000000000000001
+    Content:         746573742E64776F002F686F6D652F756D622F74657374735F323031382F3132322F69737375652F6477617266355F73706C69740062617A005F5A3362617A76006D61696E00696E7400
+  - Name:            .debug_abbrev
+    Type:            SHT_PROGBITS
+    AddressAlign:    0x0000000000000001
+    Content:         01110010177217B042251B25B442197317111B1206000000
+  - Name:            .debug_info
+    Type:            SHT_PROGBITS
+    AddressAlign:    0x0000000000000001
+    Content:         240000000500040800000000E93484C441B7E84A010000000008000000000108000000002C000000
+  - Name:            .debug_macinfo
+    Type:            SHT_PROGBITS
+    AddressAlign:    0x0000000000000001
+    Content:         '00'
+  - Name:            .debug_addr
+    Type:            SHT_PROGBITS
+    AddressAlign:    0x0000000000000001
+    Content:         '140000000500080020054000000000003005400000000000'
+  - Name:            .debug_names
+    Type:            SHT_PROGBITS
+    AddressAlign:    0x0000000000000004
+    Content:         A00000000500000001000000000000000000000004000000040000000D000000080000004C4C564D3037303000000000010000000000000003000000000000003080880B64D103B5C260880B6A7F9A7C460000003900000035000000410000000000000009000000120000001B0000002E2E03130000242403130000002435000000000000002E1A000000000000002E1A000000000000002E2600000000000000000000
+  - Name:            .debug_gnu_pubnames
+    Type:            SHT_PROGBITS
+    AddressAlign:    0x0000000000000001
+    Content:         210000000200000000002800000026000000306D61696E001A0000003062617A0000000000
+  - Name:            .debug_gnu_pubtypes
+    Type:            SHT_PROGBITS
+    AddressAlign:    0x0000000000000001
+    Content:         '17000000020000000000280000003500000090696E740000000000'
+  - Name:            .debug_line
+    Type:            SHT_PROGBITS
+    AddressAlign:    0x0000000000000001
+    Content:         71000000050008004C000000010101FB0E0D00010101010000000100000101011F010000000003011F020F051E022C000000004B61BD987753AF9C38389263DC08E24F2C000000004B61BD987753AF9C38389263DC08E24F00090220054000000000000105010A4B0500BC05030AE5750206000101
+  - Name:            .debug_line_str
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_MERGE, SHF_STRINGS ]
+    AddressAlign:    0x0000000000000001
+    Content:         2F686F6D652F756D622F74657374735F323031382F3132322F69737375652F6477617266355F73706C697400746573742E636300
+

lit/Breakpoint/split-dwarf-5-addrbase.test

+# RUN: rm -rf %t.dir
+# RUN: mkdir %t.dir
+# RUN: cd %t.dir
+# RUN: yaml2obj %p/Inputs/split-dwarf-5-addrbase.dwo.yaml > %t.dir/test.dwo
+# RUN: yaml2obj %p/Inputs/split-dwarf-5-addrbase.yaml > %t.dir/test
+# RUN: lldb-test breakpoints %t.dir/test %s | FileCheck %s
+
+# This test checks that source code location is shown correctly
+# when -gsplit-dwarf and DWARF 5 are used.
+#
+# split-dwarf-5-addrbase.dwo.yaml and split-dwarf-5-addrbase.yamlare
+# reduced yaml files produces from the dwo file and the corresponding executable.
+#
+# The following code was used initially:
+# void baz() {
+# }
+# 
+# int main() {
+#   baz();
+#   return 0;
+# }
+#
+# Invocation used to produce outputs was:
+# clang test.cc -g -fno-rtti -c -gdwarf-5 -gsplit-dwarf
+# clang test.o -g -fno-rtti -gdwarf-5 -o test -gsplit-dwarf
+# clang version 8.0.0 (trunk 347299)
+
+b baz
+# CHECK-LABEL: b baz
+# CHECK: Address: {{.*}}baz() + 4 at test.cc:2:1

source/Plugins/SymbolFile/DWARF/DWARFUnit.cpp

if (log && log->GetVerbose()) {
     else
       m_die_array[0].Dump(m_dwarf, this, strm, UINT32_MAX);
     log->PutString(strm.GetString());
   }
 }
 
 // m_die_array_mutex must be already held as read/write.
 void DWARFUnit::AddUnitDIE(const DWARFDebugInfoEntry &cu_die) {
-  SetAddrBase(
-      cu_die.GetAttributeValueAsUnsigned(m_dwarf, this, DW_AT_addr_base, 0));
+  dw_addr_t addr_base = cu_die.GetAttributeValueAsUnsigned(
+      m_dwarf, this, DW_AT_addr_base, LLDB_INVALID_ADDRESS);
+  if (addr_base != LLDB_INVALID_ADDRESS)
+    SetAddrBase(addr_base);
+
   SetRangesBase(cu_die.GetAttributeValueAsUnsigned(m_dwarf, this,
                                                    DW_AT_rnglists_base, 0));
 
   uint64_t base_addr = cu_die.GetAttributeValueAsAddress(
       m_dwarf, this, DW_AT_low_pc, LLDB_INVALID_ADDRESS);
   if (base_addr == LLDB_INVALID_ADDRESS)
     base_addr = cu_die.GetAttributeValueAsAddress(
         m_dwarf, this, DW_AT_entry_pc, 0);
void DWARFUnit::AddUnitDIE(const DWARFDebugInfoEntry &cu_die) {
   uint64_t sub_dwo_id =
       dwo_cu_die.GetAttributeValueAsUnsigned(DW_AT_GNU_dwo_id, 0);
   if (main_dwo_id != sub_dwo_id)
     return; // The 2 dwo ID isn't match. Don't use the dwo file as it belongs to
   // a differectn compilation.
 
   m_dwo_symbol_file = std::move(dwo_symbol_file);
 
-  dw_addr_t addr_base =
-      cu_die.GetAttributeValueAsUnsigned(m_dwarf, this, DW_AT_GNU_addr_base, 0);
+  // Here for DWO CU we want to use the address base set in the skeleton unit
+  // (DW_AT_addr_base) if it is available and use the DW_AT_GNU_addr_base
+  // otherwise. We do that because pre-DWARF v5 could use the DW_AT_GNU_*
+  // attributes which were applicable to the DWO units. The corresponding
+  // DW_AT_* attributes standardized in DWARF v5 are also applicable to the main
+  // unit in contrast.
+  if (addr_base == LLDB_INVALID_ADDRESS)
+    addr_base = cu_die.GetAttributeValueAsUnsigned(m_dwarf, this,
+                                                   DW_AT_GNU_addr_base, 0);
   dwo_cu->SetAddrBase(addr_base);
 
   dw_addr_t ranges_base = cu_die.GetAttributeValueAsUnsigned(
       m_dwarf, this, DW_AT_GNU_ranges_base, 0);
   dwo_cu->SetRangesBase(ranges_base);
 
   dwo_cu->SetBaseObjOffset(m_offset);
 }