[lld] 1ccde53 - [ELF] --gdb-index: support .debug_loclists

[Fangrui Song via llvm-commits]

Author: Fangrui Song
Date: 2020-04-29T15:04:13-07:00
New Revision: 1ccde533425a4ba9d379510206ad680ff9702129

URL: https://github.com/llvm/llvm-project/commit/1ccde533425a4ba9d379510206ad680ff9702129
DIFF: https://github.com/llvm/llvm-project/commit/1ccde533425a4ba9d379510206ad680ff9702129.diff

LOG: [ELF] --gdb-index: support .debug_loclists

--gdb-index currently crashes when reading a translation unit with
DWARF v5 .debug_loclists . Call stack:

```
SyntheticSections.cpp GdbIndexSection::create
SyntheticSections.cpp readAddressAreas
DWARFUnit.cpp DWARFUnit::tryExtractDIEsIfNeeded
DWARFListTable.cpp DWARFListTableHeader::extract
...
DWARFDataExtractor.cpp DWARFDataExtractor::getRelocatedValue
lld/ELF/DWARF.cpp LLDDwarfObj<ELFT>::find (sec.sec is nullptr)
...

```

This patch adds support for .debug_loclists to make `DWARFUnit::tryExtractDIEsIfNeeded` happy.
Building --gdb-index does not need .debug_loclists

Reviewed By: dblaikie, grimar

Differential Revision: https://reviews.llvm.org/D79061

Added: 
    lld/test/ELF/gdb-index-loclists.s

Modified: 
    lld/ELF/DWARF.cpp
    lld/ELF/DWARF.h

Removed: 
    


################################################################################
diff  --git a/lld/ELF/DWARF.cpp b/lld/ELF/DWARF.cpp
index bf4fff76c31f..f1587d93e53b 100644
--- a/lld/ELF/DWARF.cpp
+++ b/lld/ELF/DWARF.cpp
@@ -36,6 +36,7 @@ template <class ELFT> LLDDwarfObj<ELFT>::LLDDwarfObj(ObjFile<ELFT> *obj) {
                 .Case(".debug_gnu_pubnames", &gnuPubnamesSection)
                 .Case(".debug_gnu_pubtypes", &gnuPubtypesSection)
                 .Case(".debug_info", &infoSection)
+                .Case(".debug_loclists", &loclistsSection)
                 .Case(".debug_ranges", &rangesSection)
                 .Case(".debug_rnglists", &rnglistsSection)
                 .Case(".debug_str_offsets", &strOffsetsSection)

diff  --git a/lld/ELF/DWARF.h b/lld/ELF/DWARF.h
index 51ec9092f172..8609e35faf95 100644
--- a/lld/ELF/DWARF.h
+++ b/lld/ELF/DWARF.h
@@ -32,6 +32,10 @@ template <class ELFT> class LLDDwarfObj final : public llvm::DWARFObject {
     f(infoSection);
   }
 
+  const llvm::DWARFSection &getLoclistsSection() const override {
+    return loclistsSection;
+  }
+
   const llvm::DWARFSection &getRangesSection() const override {
     return rangesSection;
   }
@@ -81,6 +85,7 @@ template <class ELFT> class LLDDwarfObj final : public llvm::DWARFObject {
   LLDDWARFSection gnuPubnamesSection;
   LLDDWARFSection gnuPubtypesSection;
   LLDDWARFSection infoSection;
+  LLDDWARFSection loclistsSection;
   LLDDWARFSection rangesSection;
   LLDDWARFSection rnglistsSection;
   LLDDWARFSection strOffsetsSection;

diff  --git a/lld/test/ELF/gdb-index-loclists.s b/lld/test/ELF/gdb-index-loclists.s
new file mode 100644
index 000000000000..e3769b695372
--- /dev/null
+++ b/lld/test/ELF/gdb-index-loclists.s
@@ -0,0 +1,37 @@
+# REQUIRES: x86
+## Regression test that we don't crash on DWARF v5 .debug_loclists
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64 %s -o %t.o
+# RUN: ld.lld --gdb-index %t.o -o /dev/null
+
+.section .debug_abbrev,"", at progbits
+  .byte 1            # Abbreviation Code
+  .byte 17           # DW_TAG_compile_unit
+  .byte 0            # DW_CHILDREN_no
+  .ascii "\214\001"  # DW_AT_loclists_base
+  .byte 23           # DW_FORM_sec_offset
+  .byte 0            # EOM(1)
+  .byte 0            # EOM(2)
+  .byte 0
+
+.section .debug_info,"", at progbits
+.Lcu_begin0:
+  .long .Lcu_end0-.Lcu_begin0-4  # Length of Unit
+  .short 5                       # DWARF version number
+  .byte  1                       # DWARF Unit Type
+  .byte  8                       # Address Size
+  .long  0                       # Offset Into Abbrev. Section
+  .byte  1                       # Abbrev [1] DW_TAG_compile_unit
+  .long  .Lloclists_table_base0  # DW_AT_loclists_base
+.Lcu_end0:
+
+.section .debug_loclists,"", at progbits
+  .long .Ldebug_loclist_table_end0-.Ldebug_loclist_table_start0 # Length
+.Ldebug_loclist_table_start0:
+  .short 5                # Version
+  .byte  8                # Address size
+  .byte  0                # Segment selector size
+  .long  0                # Offset entry count
+.Lloclists_table_base0:
+  .byte  0                # DW_LLE_end_of_list
+.Ldebug_loclist_table_end0: