[llvm] 42874f6 - [DebugInfo] Fix detection of hash collision in Apple Accel tables

[Felipe de Azevedo Piovezan via llvm-commits]

Author: Felipe de Azevedo Piovezan
Date: 2023-06-15T12:35:48-04:00
New Revision: 42874f66475548541cd871d5790116b2bc68b89a

URL: https://github.com/llvm/llvm-project/commit/42874f66475548541cd871d5790116b2bc68b89a
DIFF: https://github.com/llvm/llvm-project/commit/42874f66475548541cd871d5790116b2bc68b89a.diff

LOG: [DebugInfo] Fix detection of hash collision in Apple Accel tables

The current implementation was ignoring the possibility of collisions.

Added: 
    llvm/test/DebugInfo/Generic/apple-names-hash-collisions.ll

Modified: 
    llvm/lib/DebugInfo/DWARF/DWARFAcceleratorTable.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/DebugInfo/DWARF/DWARFAcceleratorTable.cpp b/llvm/lib/DebugInfo/DWARF/DWARFAcceleratorTable.cpp
index cda822d92aead..03bc8a835b4b8 100644
--- a/llvm/lib/DebugInfo/DWARF/DWARFAcceleratorTable.cpp
+++ b/llvm/lib/DebugInfo/DWARF/DWARFAcceleratorTable.cpp
@@ -333,22 +333,19 @@ AppleAcceleratorTable::equal_range(StringRef Key) const {
     return EmptyRange;
 
   std::optional<uint32_t> StrOffset = readStringOffsetAt(DataOffset);
-
-  // Invalid input or no more strings in this hash.
-  if (!StrOffset || *StrOffset == 0)
-    return EmptyRange;
-
-  std::optional<StringRef> MaybeStr = readStringFromStrSection(*StrOffset);
-  std::optional<uint32_t> NumEntries = this->readU32FromAccel(DataOffset);
-  if (!MaybeStr || !NumEntries)
-    return EmptyRange;
-  if (Key == *MaybeStr) {
+  // Valid input and still have strings in this hash.
+  while (StrOffset && *StrOffset) {
+    std::optional<StringRef> MaybeStr = readStringFromStrSection(*StrOffset);
+    std::optional<uint32_t> NumEntries = this->readU32FromAccel(DataOffset);
+    if (!MaybeStr || !NumEntries)
+      return EmptyRange;
     uint64_t EndOffset = DataOffset + *NumEntries * getHashDataEntryLength();
-    return make_range({*this, DataOffset}, ValueIterator{*this, EndOffset});
+    if (Key == *MaybeStr)
+      return make_range({*this, DataOffset}, ValueIterator{*this, EndOffset});
+    DataOffset = EndOffset;
+    StrOffset = readStringOffsetAt(DataOffset);
   }
 
-  // FIXME: this shouldn't return, we haven't checked all the colliding strings
-  // in the bucket!
   return EmptyRange;
 }
 

diff  --git a/llvm/test/DebugInfo/Generic/apple-names-hash-collisions.ll b/llvm/test/DebugInfo/Generic/apple-names-hash-collisions.ll
new file mode 100644
index 0000000000000..5e20127a2e2ca
--- /dev/null
+++ b/llvm/test/DebugInfo/Generic/apple-names-hash-collisions.ll
@@ -0,0 +1,36 @@
+; RUN: %llc_dwarf -accel-tables=Apple -filetype=obj -o %t < %s
+; RUN: llvm-dwarfdump -apple-names %t | FileCheck %s --check-prefix=NUM_HASHES
+; RUN: llvm-dwarfdump  --find=bb --find=cA %t | FileCheck %s --check-prefix=FOUND_VARS
+
+
+; The strings 'bb' and 'cA' hash to the same value under the Apple accelerator
+; table hashing algorithm.
+; We first test that there is exactly one bucket and one hash.
+; Then we check that both values are found.
+
+; NUM_HASHES:      Bucket count: 1
+; NUM_HASHES-NEXT: Hashes count: 1
+; FOUND_VARS: DW_AT_name        ("bb")
+; FOUND_VARS: DW_AT_name        ("cA")
+
+ at bb = global i32 200, align 4, !dbg !0
+ at cA = global i32 10, align 4, !dbg !5
+
+!llvm.module.flags = !{!9, !10, !11, !12, !13}
+!llvm.dbg.cu = !{!2}
+!llvm.ident = !{!15}
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "bb", scope: !2, file: !3, line: 1, type: !7, isDefinition: true)
+!2 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !3, producer: "", emissionKind: FullDebug, globals: !4)
+!3 = !DIFile(filename: "test.cpp", directory: "blah")
+!4 = !{!0, !5}
+!5 = !DIGlobalVariableExpression(var: !6, expr: !DIExpression())
+!6 = distinct !DIGlobalVariable(name: "cA", scope: !2, file: !3, line: 2, type: !7, isLocal: false, isDefinition: true)
+!7 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!9 = !{i32 7, !"Dwarf Version", i32 4}
+!10 = !{i32 2, !"Debug Info Version", i32 3}
+!11 = !{i32 1, !"wchar_size", i32 4}
+!12 = !{i32 8, !"PIC Level", i32 2}
+!13 = !{i32 7, !"uwtable", i32 1}
+!15 = !{!"blah"}