[LLD] - Do not crash when reporting errors when .debug_line_str (DWARF5) is used.

[grimar]

Summary

Imagine we have the following code:

int foo();
int main() { return foo(); }

It will crash if you try to compile it with`clang -O0 -gdwarf-5 test.cpp -o test -g -fuse-ld=lld`

The crash happens inside the LLVM DWARF parser because LLD does not provide the .debug_line_str section.
At the same time for correct parsing and reporting, we anyways need to provide this section from our side.
The patch fixes the issue.

[ruiu]

LGTM

[grimar]

r343667

ELF/DWARF.h

public:
 
   const llvm::DWARFSection &getLineSection() const override {
     return LineSection;
   }
 
   StringRef getFileName() const override { return ""; }
   StringRef getAbbrevSection() const override { return AbbrevSection; }
   StringRef getStringSection() const override { return StrSection; }
+  StringRef getLineStringSection() const override { return LineStringSection; }
 
   StringRef getGnuPubNamesSection() const override {
     return GnuPubNamesSection;
   }
 
   StringRef getGnuPubTypesSection() const override {
     return GnuPubTypesSection;
   }
private:
   LLDDWARFSection InfoSection;
   LLDDWARFSection RangeSection;
   LLDDWARFSection LineSection;
 
   StringRef AbbrevSection;
   StringRef GnuPubNamesSection;
   StringRef GnuPubTypesSection;
   StringRef StrSection;
+  StringRef LineStringSection;
 };
 
 } // namespace elf
 } // namespace lld
 
 #endif

ELF/DWARF.cpp

for (InputSectionBase *Sec : Obj->getSections()) {
     if (Sec->Name == ".debug_abbrev")
       AbbrevSection = toStringRef(Sec->Data);
     else if (Sec->Name == ".debug_gnu_pubnames")
       GnuPubNamesSection = toStringRef(Sec->Data);
     else if (Sec->Name == ".debug_gnu_pubtypes")
       GnuPubTypesSection = toStringRef(Sec->Data);
     else if (Sec->Name == ".debug_str")
       StrSection = toStringRef(Sec->Data);
+    if (Sec->Name == ".debug_line_str")
+      LineStringSection = toStringRef(Sec->Data);
   }
 }
 
 // Find if there is a relocation at Pos in Sec.  The code is a bit
 // more complicated than usual because we need to pass a section index
 // to llvm since it has no idea about InputSection.
 template <class ELFT>
 template <class RelTy>

test/ELF/debug-line-str.s

+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux -dwarf-version=5 %s -o %t.o
+# RUN: not ld.lld %t.o -o %t1 2>&1 | FileCheck %s
+
+# Check we do not crash and able to report the source location.
+
+# CHECK:      error: undefined symbol: foo()
+# CHECK-NEXT: >>> referenced by test.cpp:3
+# CHECK-NEXT: >>>               {{.*}}.o:(.text+0x1)
+
+# The code below is the reduced version of the output
+# from the following invocation and source:
+#
+# // test.cpp:
+# int foo();
+# int main() {
+#   return foo();
+# }
+#
+# clang -gdwarf-5 test.cpp -o test.s -S
+# clang version 8.0.0 (trunk 343487)
+
+.text
+.file "test.cpp"
+.globl main
+.type main,@function
+main:
+.Lfunc_begin0:
+ .file 0 "/home/path" "test.cpp" md5 0x8ed32099ab837bd13543fd3e8102739f
+ .file 1 "test.cpp" md5 0x8ed32099ab837bd13543fd3e8102739f
+ .loc 1 3 10 prologue_end
+ jmp _Z3foov
+.Lfunc_end0:
+
+.Lstr_offsets_base0:
+.section .debug_str,"MS",@progbits,1
+ .asciz "stub"
+
+.section .debug_str_offsets,"",@progbits
+ .long 0
+
+.section .debug_abbrev,"",@progbits
+ .byte 1                           # Abbreviation Code
+ .byte 17                          # DW_TAG_compile_unit
+ .byte 0                           # DW_CHILDREN_yes
+ .byte 37                          # DW_AT_producer
+ .byte 37                          # DW_FORM_strx1
+ .byte 19                          # DW_AT_language
+ .byte 5                           # DW_FORM_data2
+ .byte 3                           # DW_AT_name
+ .byte 37                          # DW_FORM_strx1
+ .byte 114                         # DW_AT_str_offsets_base
+ .byte 23                          # DW_FORM_sec_offset
+ .byte 16                          # DW_AT_stmt_list
+ .byte 23                          # DW_FORM_sec_offset
+ .byte 27                          # DW_AT_comp_dir
+ .byte 37                          # DW_FORM_strx1
+ .byte 17                          # DW_AT_low_pc
+ .byte 1                           # DW_FORM_addr
+ .byte 18                          # DW_AT_high_pc
+ .byte 6                           # DW_FORM_data4
+ .byte 0                           # EOM(1)
+ .byte 0                           # EOM(2)
+
+ .byte 2                           # Abbreviation Code
+ .byte 46                          # DW_TAG_subprogram
+ .byte 0                           # DW_CHILDREN_no
+ .byte 17                          # DW_AT_low_pc
+ .byte 1                           # DW_FORM_addr
+ .byte 18                          # DW_AT_high_pc
+ .byte 6                           # DW_FORM_data4
+ .byte 64                          # DW_AT_frame_base
+ .byte 24                          # DW_FORM_exprloc
+ .byte 3                           # DW_AT_name
+ .byte 37                          # DW_FORM_strx1
+ .byte 58                          # DW_AT_decl_file
+ .byte 11                          # DW_FORM_data1
+ .byte 59                          # DW_AT_decl_line
+ .byte 11                          # DW_FORM_data1
+ .byte 73                          # DW_AT_type
+ .byte 19                          # DW_FORM_ref4
+ .byte 63                          # DW_AT_external
+ .byte 25                          # DW_FORM_flag_present
+ .byte 0                           # EOM(1)
+ .byte 0                           # EOM(2)
+
+ .byte 3                           # Abbreviation Code
+ .byte 36                          # DW_TAG_base_type
+ .byte 0                           # DW_CHILDREN_no
+ .byte 3                           # DW_AT_name
+ .byte 37                          # DW_FORM_strx1
+ .byte 62                          # DW_AT_encoding
+ .byte 11                          # DW_FORM_data1
+ .byte 11                          # DW_AT_byte_size
+ .byte 11                          # DW_FORM_data1
+ .byte 0                           # EOM(1)
+ .byte 0                           # EOM(2)
+ .byte 0                           # EOM(3)
+
+.section .debug_info,"",@progbits
+.Lcu_begin0:
+ .long 61                         # Length of Unit
+ .short 5                         # DWARF version number
+ .byte  1                         # DWARF Unit Type
+ .byte  8                         # Address Size (in bytes)
+ .long  .debug_abbrev             # Offset Into Abbrev. Section
+
+ .byte  1                         # Abbrev [1] 0xc:0x35 DW_TAG_compile_unit
+ .byte  0                         # DW_AT_producer
+ .short 0                         # DW_AT_language
+ .byte  0                         # DW_AT_name
+ .long  .Lstr_offsets_base0       # DW_AT_str_offsets_base
+ .long  .Lline_table_start0       # DW_AT_stmt_list
+ .byte  0                         # DW_AT_comp_dir
+ .quad  .Lfunc_begin0             # DW_AT_low_pc
+ .long  .Lfunc_end0-.Lfunc_begin0 # DW_AT_high_pc
+ 
+ .byte  2                         # Abbrev [2] 0x26:0x16 DW_TAG_subprogram
+ .quad  .Lfunc_begin0             # DW_AT_low_pc
+ .long  .Lfunc_end0-.Lfunc_begin0 # DW_AT_high_pc
+ .byte  1                         # DW_AT_frame_base
+ .byte  87
+ .byte  0                         # DW_AT_name
+ .byte  1                         # DW_AT_decl_file
+ .byte  2                         # DW_AT_decl_line
+ .long  60                        # DW_AT_type
+                                  # DW_AT_external
+
+ .byte  3                         # Abbrev [3] 0x3c:0x4 DW_TAG_base_type
+ .byte  0                         # DW_AT_name
+ .byte  5                         # DW_AT_encoding
+ .byte  4                         # DW_AT_byte_size
+ .byte  0                         # End Of Children Mark
+
+.section .debug_line,"",@progbits
+.Lline_table_start0: