Index: ELF/SyntheticSections.cpp
===================================================================
--- ELF/SyntheticSections.cpp
+++ ELF/SyntheticSections.cpp
@@ -2367,6 +2367,8 @@
 
     ArrayRef<InputSectionBase *> Sections = Sec->File->getSections();
     for (DWARFAddressRange &R : *Ranges) {
+      if (R.SectionIndex == -1ULL)
+        continue;
       InputSectionBase *S = Sections[R.SectionIndex];
       if (!S || S == &InputSection::Discarded || !S->Live)
         continue;
Index: test/ELF/gdb-index-invalid-section-index.yaml
===================================================================
--- /dev/null
+++ test/ELF/gdb-index-invalid-section-index.yaml
@@ -0,0 +1,139 @@
+# RUN: yaml2obj %s -o %t.o
+# RUN: ld.lld --gdb-index %t.o -o /dev/null
+
+## We used to crash if a DWARFAddressRange has invalid SectionIndex (-1).
+
+--- !ELF
+FileHeader:
+  Class:           ELFCLASS64
+  Data:            ELFDATA2LSB
+  Type:            ET_REL
+  Machine:         EM_X86_64
+Sections:
+  - Name:            .text
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC, SHF_EXECINSTR ]
+    AddressAlign:    0x0000000000000010
+    Content:         31C0C3
+  - Name:            .debug_str_offsets
+    Type:            SHT_PROGBITS
+    AddressAlign:    0x0000000000000001
+    Content:         '1000000005000000000000000000000000000000'
+  - Name:            .rela.debug_str_offsets
+    Type:            SHT_RELA
+    Link:            .symtab
+    AddressAlign:    0x0000000000000008
+    EntSize:         0x0000000000000018
+    Info:            .debug_str_offsets
+    Relocations:
+      - Offset:          0x0000000000000008
+        Symbol:          .debug_str
+        Type:            R_X86_64_32
+      - Offset:          0x000000000000000C
+        Symbol:          .debug_str
+        Type:            R_X86_64_32
+        Addend:          1
+      - Offset:          0x0000000000000010
+        Symbol:          .debug_str
+        Type:            R_X86_64_32
+        Addend:          6
+  - Name:            .debug_str
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_MERGE, SHF_STRINGS ]
+    AddressAlign:    0x0000000000000001
+    EntSize:         0x0000000000000001
+    Content:         00612E6363002F746D7000
+  - Name:            .debug_abbrev
+    Type:            SHT_PROGBITS
+    AddressAlign:    0x0000000000000001
+    Content:         011100252513050325721710171B25111B1206000000
+  - Name:            .debug_info
+    Type:            SHT_PROGBITS
+    AddressAlign:    0x0000000000000001
+    Content:         1B000000050001080000000001000400010000000000000000020003000000
+  - Name:            .rela.debug_info
+    Type:            SHT_RELA
+    Link:            .symtab
+    AddressAlign:    0x0000000000000008
+    EntSize:         0x0000000000000018
+    Info:            .debug_info
+    Relocations:
+      - Offset:          0x0000000000000008
+        Symbol:          .debug_abbrev
+        Type:            R_X86_64_32
+      - Offset:          0x0000000000000011
+        Symbol:          .debug_str_offsets
+        Type:            R_X86_64_32
+        Addend:          8
+      - Offset:          0x0000000000000015
+        Symbol:          .debug_line
+        Type:            R_X86_64_32
+  - Name:            .debug_addr
+    Type:            SHT_PROGBITS
+    AddressAlign:    0x0000000000000001
+    Content:         0C000000050008000000000000000000
+  - Name:            .rela.debug_addr
+    Type:            SHT_RELA
+    Link:            .symtab
+    AddressAlign:    0x0000000000000008
+    EntSize:         0x0000000000000018
+    Info:            .debug_addr
+    Relocations:
+      - Offset:          0x0000000000000008
+        Symbol:          .text
+        Type:            R_X86_64_64
+  - Name:            .debug_line
+    Type:            SHT_PROGBITS
+    AddressAlign:    0x0000000000000001
+    Content:         2D0000000500080025000000010101FB0E0D00010101010000000100000101011F010000000002011F020F010000000000
+  - Name:            .rela.debug_line
+    Type:            SHT_RELA
+    Link:            .symtab
+    AddressAlign:    0x0000000000000008
+    EntSize:         0x0000000000000018
+    Info:            .debug_line
+    Relocations:
+      - Offset:          0x0000000000000022
+        Symbol:          .debug_line_str
+        Type:            R_X86_64_32
+      - Offset:          0x000000000000002C
+        Symbol:          .debug_line_str
+        Type:            R_X86_64_32
+        Addend:          5
+  - Name:            .debug_line_str
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_MERGE, SHF_STRINGS ]
+    AddressAlign:    0x0000000000000001
+    EntSize:         0x0000000000000001
+    Content:         2F746D7000612E636300
+Symbols:
+  - Name:            a.ll
+    Type:            STT_FILE
+    Index:           SHN_ABS
+  - Name:            .text
+    Type:            STT_SECTION
+    Section:         .text
+  - Name:            .debug_str_offsets
+    Type:            STT_SECTION
+    Section:         .debug_str_offsets
+  - Name:            .debug_str
+    Type:            STT_SECTION
+    Section:         .debug_str
+  - Name:            .debug_abbrev
+    Type:            STT_SECTION
+    Section:         .debug_abbrev
+  - Name:            .debug_info
+    Type:            STT_SECTION
+    Section:         .debug_info
+  - Name:            .debug_line
+    Type:            STT_SECTION
+    Section:         .debug_line
+  - Name:            .debug_line_str
+    Type:            STT_SECTION
+    Section:         .debug_line_str
+  - Name:            foo
+    Type:            STT_FUNC
+    Section:         .text
+    Binding:         STB_GLOBAL
+    Size:            0x0000000000000003
+...