ELF: --gdb-index: Change findSection to return an InputSection.

We should only ever expect this function to return a regular
InputSection; I would not expect a function definition to be in a
MergeInputSection or EhInputSection. We were previously crashing
in writeTo if this function returned a section that was not an
InputSection because we do not set OutSec for such sections.

This can happen in practice if a function is defined in an empty
section which shares its offset-in-file with a MergeInputSection,
as in the provided test case.

A better fix for this bug would be to fix the
DWARFUnit::collectAddressRanges() interface to provide section
information (see D33183), but this at least fixes the crash.

Differential Revision: https://reviews.llvm.org/D33176

llvm-svn: 303089

diff --git a/lld/ELF/GdbIndex.h b/lld/ELF/GdbIndex.h
index a36b927..03fec64 100644 (file)
--- a/lld/ELF/GdbIndex.h
+++ b/lld/ELF/GdbIndex.h
@@ -21,7 +21,7 @@ class InputSection;
 
 // Struct represents single entry of address area of gdb index.
 struct AddressEntry {
-  InputSectionBase *Section;
+  InputSection *Section;
   uint64_t LowAddress;
   uint64_t HighAddress;
   size_t CuIndex;

diff --git a/lld/ELF/SyntheticSections.cpp b/lld/ELF/SyntheticSections.cpp
index a42d158..a9456ad 100644 (file)
--- a/lld/ELF/SyntheticSections.cpp
+++ b/lld/ELF/SyntheticSections.cpp
@@ -1701,13 +1701,14 @@ readCuList(DWARFContext &Dwarf, InputSection *Sec) {
   return Ret;
 }
 
-static InputSectionBase *findSection(ArrayRef<InputSectionBase *> Arr,
-                                     uint64_t Offset) {
+static InputSection *findSection(ArrayRef<InputSectionBase *> Arr,
+                                 uint64_t Offset) {
   for (InputSectionBase *S : Arr)
-    if (S && S != &InputSection::Discarded && S->Live)
-      if (Offset >= S->getOffsetInFile() &&
-          Offset < S->getOffsetInFile() + S->getSize())
-        return S;
+    if (auto *IS = dyn_cast_or_null<InputSection>(S))
+      if (IS != &InputSection::Discarded && IS->Live &&
+          Offset >= IS->getOffsetInFile() &&
+          Offset < IS->getOffsetInFile() + IS->getSize())
+        return IS;
   return nullptr;
 }
 
@@ -1721,7 +1722,7 @@ readAddressArea(DWARFContext &Dwarf, InputSection *Sec, size_t CurrentCU) {
 
     ArrayRef<InputSectionBase *> Sections = Sec->File->getSections();
     for (std::pair<uint64_t, uint64_t> &R : Ranges)
-      if (InputSectionBase *S = findSection(Sections, R.first))
+      if (InputSection *S = findSection(Sections, R.first))
         Ret.push_back({S, R.first - S->getOffsetInFile(),
                        R.second - S->getOffsetInFile(), CurrentCU});
     ++CurrentCU;

diff --git a/lld/test/ELF/gdb-index-empty.s b/lld/test/ELF/gdb-index-empty.s
new file mode 100644 (file)
index 0000000..933afed
--- /dev/null
+++ b/lld/test/ELF/gdb-index-empty.s
@@ -0,0 +1,116 @@
+# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux -o %t %s
+# RUN: ld.lld --gdb-index --gc-sections -o %t2 %t
+# RUN: llvm-dwarfdump -debug-dump=gdb_index %t2 | FileCheck %s
+
+# CHECK: Address area offset = 0x28, has 0 entries:
+
+# Generated with: (clang r302976)
+# echo "void _start() { __builtin_unreachable(); }" | \
+# clang -Os -g -S -o gdb-index-empty.s -x c - -Xclang -fdebug-compilation-dir -Xclang .
+
+       .text
+       .file   "-"
+       .globl  _start
+       .type   _start,@function
+_start:                                 # @_start
+.Lfunc_begin0:
+       .cfi_startproc
+# BB#0:                                 # %entry
+.Lfunc_end0:
+       .size   _start, .Lfunc_end0-_start
+       .cfi_endproc
+
+       .file   1 "<stdin>"
+       .section        .debug_str,"MS",@progbits,1
+.Linfo_string0:
+       .asciz  "clang version 5.0.0 "  # string offset=0
+.Linfo_string1:
+       .asciz  "-"                     # string offset=21
+.Linfo_string2:
+       .asciz  "."                     # string offset=23
+.Linfo_string3:
+       .asciz  "_start"                # string offset=25
+       .section        .debug_loc,"",@progbits
+       .section        .debug_abbrev,"",@progbits
+       .byte   1                       # Abbreviation Code
+       .byte   17                      # DW_TAG_compile_unit
+       .byte   1                       # DW_CHILDREN_yes
+       .byte   37                      # DW_AT_producer
+       .byte   14                      # DW_FORM_strp
+       .byte   19                      # DW_AT_language
+       .byte   5                       # DW_FORM_data2
+       .byte   3                       # DW_AT_name
+       .byte   14                      # DW_FORM_strp
+       .byte   16                      # DW_AT_stmt_list
+       .byte   23                      # DW_FORM_sec_offset
+       .byte   27                      # DW_AT_comp_dir
+       .byte   14                      # DW_FORM_strp
+       .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   14                      # DW_FORM_strp
+       .byte   58                      # DW_AT_decl_file
+       .byte   11                      # DW_FORM_data1
+       .byte   59                      # DW_AT_decl_line
+       .byte   11                      # DW_FORM_data1
+       .byte   63                      # DW_AT_external
+       .byte   25                      # DW_FORM_flag_present
+       .byte   0                       # EOM(1)
+       .byte   0                       # EOM(2)
+       .byte   0                       # EOM(3)
+       .section        .debug_info,"",@progbits
+.Lcu_begin0:
+       .long   60                      # Length of Unit
+       .short  4                       # DWARF version number
+       .long   .debug_abbrev           # Offset Into Abbrev. Section
+       .byte   8                       # Address Size (in bytes)
+       .byte   1                       # Abbrev [1] 0xb:0x35 DW_TAG_compile_unit
+       .long   .Linfo_string0          # DW_AT_producer
+       .short  12                      # DW_AT_language
+       .long   .Linfo_string1          # DW_AT_name
+       .long   .Lline_table_start0     # DW_AT_stmt_list
+       .long   .Linfo_string2          # DW_AT_comp_dir
+       .quad   .Lfunc_begin0           # DW_AT_low_pc
+       .long   .Lfunc_end0-.Lfunc_begin0 # DW_AT_high_pc
+       .byte   2                       # Abbrev [2] 0x2a:0x15 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
+       .long   .Linfo_string3          # DW_AT_name
+       .byte   1                       # DW_AT_decl_file
+       .byte   1                       # DW_AT_decl_line
+                                        # DW_AT_external
+       .byte   0                       # End Of Children Mark
+       .section        .debug_ranges,"",@progbits
+       .section        .debug_macinfo,"",@progbits
+.Lcu_macro_begin0:
+       .byte   0                       # End Of Macro List Mark
+       .section        .debug_pubnames,"",@progbits
+       .long   .LpubNames_end0-.LpubNames_begin0 # Length of Public Names Info
+.LpubNames_begin0:
+       .short  2                       # DWARF Version
+       .long   .Lcu_begin0             # Offset of Compilation Unit Info
+       .long   64                      # Compilation Unit Length
+       .long   42                      # DIE offset
+       .asciz  "_start"                # External Name
+       .long   0                       # End Mark
+.LpubNames_end0:
+
+       .ident  "clang version 5.0.0 "
+       .section        ".note.GNU-stack","",@progbits
+       .section        .debug_line,"",@progbits
+.Lline_table_start0: