Index: llvm/lib/DebugInfo/DWARF/DWARFUnitIndex.cpp
===================================================================
--- llvm/lib/DebugInfo/DWARF/DWARFUnitIndex.cpp
+++ llvm/lib/DebugInfo/DWARF/DWARFUnitIndex.cpp
@@ -286,10 +286,14 @@
 
   auto H = S & Mask;
   auto HP = ((S >> 32) & Mask) | 1;
-  while (Rows[H].getSignature() != S && Rows[H].getSignature() != 0)
+  // The spec says "while 0 is a valid hash value, the row index in a used slot
+  // will always be non-zero". Loop until we find a match or an empty slot.
+  while (Rows[H].getSignature() != S && Rows[H].Index != nullptr)
     H = (H + HP) & Mask;
 
-  if (Rows[H].getSignature() != S)
+  // If the slot is empty, we don't care whether the signature matches (it could
+  // be zero and still match the zeros in the empty slot).
+  if (Rows[H].Index == nullptr)
     return nullptr;
 
   return &Rows[H];
Index: llvm/test/tools/llvm-symbolizer/split-dwarf-zero-signature-not-found.s
===================================================================
--- /dev/null
+++ llvm/test/tools/llvm-symbolizer/split-dwarf-zero-signature-not-found.s
@@ -0,0 +1,112 @@
+# REQUIRES: x86-registered-target
+
+# RUN: llvm-mc --filetype=obj --triple x86_64-pc-linux %s -o %t --defsym MAIN=0
+# RUN: llvm-mc --filetype=obj --triple x86_64-pc-linux %s -o %t.dwp --defsym DWP=0
+# RUN: llvm-symbolizer --obj=%t --dwp=%t.dwp 0x0 | FileCheck %s
+# CHECK-NOT: Stack dump
+
+        .section        .debug_abbrev,"",@progbits
+        .byte   1                       # Abbreviation Code
+        .byte   17                      # DW_TAG_compile_unit
+        .byte   0                       # DW_CHILDREN_no
+        .ascii  "\260B"                 # DW_AT_GNU_dwo_name
+        .byte   8                       # DW_FORM_string
+        .ascii  "\261B"                 # DW_AT_GNU_dwo_id
+        .byte   7                       # DW_FORM_data8
+        .ascii  "\263B"                 # DW_AT_GNU_addr_base
+        .byte   23                      # DW_FORM_sec_offset
+        .byte   85                      # DW_AT_ranges
+        .byte   23                      # DW_FORM_sec_offset
+        .byte   0                       # EOM(1)
+        .byte   0                       # EOM(2)
+        .byte   0                       # EOM(3)
+
+# Create two CUs, with dwo_ids 0 and 1 respectively.
+.ifdef MAIN
+.irpc I,01
+        .text
+F\I:
+        nop
+
+        .section        .debug_info,"",@progbits
+.Lcu_begin\I:
+        .long   .Ldebug_info_end\I-.Ldebug_info_start\I # Length of Unit
+.Ldebug_info_start\I:
+        .short  4                       # DWARF version number
+        .long   .debug_abbrev           # Offset Into Abbrev. Section
+        .byte   8                       # Address Size (in bytes)
+        .byte   1                       # Abbrev [1] 0xb:0x25 DW_TAG_compile_unit
+        .asciz  "A.dwo"                 # DW_AT_GNU_dwo_name
+        .quad   \I                      # DW_AT_GNU_dwo_id
+        .long   .debug_addr             # DW_AT_GNU_addr_base
+        .long   .Lranges\I              # DW_AT_ranges
+.Ldebug_info_end\I:
+
+        .section        .debug_addr,"",@progbits
+        .quad   A\I
+        .quad   F\I
+
+        .section        .debug_ranges,"",@progbits
+.Lranges\I:
+        .quad   F\I
+        .quad   F\I+1
+        .quad   0
+        .quad   0
+.endr
+.endif
+
+.ifdef DWP
+# This deliberately excludes compile unit 0. We want to check the case where a
+# signature = 0 matches an empty hash slot in .debug_cu_index and the index in
+# the parallel table has to be checked.
+.irpc I,1
+        .section        .debug_abbrev.dwo,"e",@progbits
+.Labbrev\I:
+        .byte   \I*10+1                 # Abbreviation Code
+        .byte   17                      # DW_TAG_compile_unit
+        .byte   0                       # DW_CHILDREN_no
+        .byte   37                      # DW_AT_producer
+        .byte   8                       # DW_FORM_string
+        .byte   3                       # DW_AT_name
+        .byte   8                       # DW_FORM_string
+        .byte   0                       # EOM(1)
+        .byte   0                       # EOM(2)
+        .byte   0                       # EOM(3)
+.Labbrev_end\I:
+
+        .section        .debug_info.dwo,"e",@progbits
+.Lcu_begin\I:
+        .long   .Ldebug_info_end\I-.Ldebug_info_start\I # Length of Unit
+.Ldebug_info_start\I:
+        .short  4                       # DWARF version number
+        .long   0                       # Offset Into Abbrev. Section
+        .byte   8                       # Address Size (in bytes)
+        .byte   \I*10+1                 # Abbrev DW_TAG_compile_unit
+        .asciz  "Hand-written DWARF"    # DW_AT_producer
+        .byte   '0'+\I, '.', 'c', 0     # DW_AT_name
+.Ldebug_info_end\I:
+.endr
+
+        .section        .debug_cu_index,"",@progbits
+        .short  2                       # DWARF version number
+        .short  0                       # Reserved
+        .long   2                       # Section count
+        .long   1                       # Unit count
+        .long   8                       # Slot count
+
+        .quad   1, 0, 0, 0, 0, 0, 0, 0  # Hash table
+        .long   1, 0, 0, 0, 0, 0, 0, 0  # Index table
+
+        .long   1                       # DW_SECT_INFO
+        .long   3                       # DW_SECT_ABBREV
+
+.irpc I,1
+        .long .Lcu_begin\I-.debug_info.dwo
+        .long .Labbrev\I-.debug_abbrev.dwo
+.endr
+.irpc I,1
+        .long .Ldebug_info_end\I-.Lcu_begin\I
+        .long .Labbrev_end\I-.Labbrev\I
+.endr
+
+.endif