[gsymutil] Fix how invalid LLVM_stmt_seq is set and used (llvm#164015)

Previously, invalid offset is set to UINT64_MAX, this is not right when
DWARF32, which leads to incorrect debug into in GSYM, the branch:

```
    if (StmtSeqVal != UNIT64_MAX)
      StmtSeqOffset = StmtSeqVal;
```

will always be true.

In this PR, [commit
1](llvm@b1983d6)
sets up a test that demonstrates the problem, [commit
2](llvm@0d58ce4)
fixes it.

[Diffing commit 1 and
2](llvm@0d58ce4#diff-019bdbc9922ad34fdfbcb524a9805f5af26c432540e76b87a6a5f73d9e0e853aL44)
in this PR shows how after the PR the symbolicated line number changed
from function definition to function body

Author: DataCorrupted

llvm/include/llvm/BinaryFormat/Dwarf.h

@@ -1128,6 +1128,9 @@ struct FormParams {
   uint8_t getDwarfOffsetByteSize() const {
     return dwarf::getDwarfOffsetByteSize(Format);
   }
+  inline uint64_t getDwarfMaxOffset() const {
+    return (getDwarfOffsetByteSize() == 4) ? UINT32_MAX : UINT64_MAX;
+  }
 
   explicit operator bool() const { return Version && AddrSize; }
 };

llvm/lib/DWARFLinker/Classic/DWARFLinker.cpp

@@ -2427,11 +2427,13 @@ void DWARFLinker::DIECloner::generateLineTableForUnit(CompileUnit &Unit) {
           uint64_t OrigStmtSeq = StmtSeq.get();
           // 1. Get the original row index from the stmt list offset.
           auto OrigRowIter = SeqOffToOrigRow.find(OrigStmtSeq);
+          const uint64_t InvalidOffset =
+              Unit.getOrigUnit().getFormParams().getDwarfMaxOffset();
           // Check whether we have an output sequence for the StmtSeq offset.
           // Some sequences are discarded by the DWARFLinker if they are invalid
           // (empty).
           if (OrigRowIter == SeqOffToOrigRow.end()) {
-            StmtSeq.set(UINT64_MAX);
+            StmtSeq.set(InvalidOffset);
             continue;
           }
           size_t OrigRowIndex = OrigRowIter->second;
@@ -2441,7 +2443,7 @@ void DWARFLinker::DIECloner::generateLineTableForUnit(CompileUnit &Unit) {
           if (NewRowIter == OrigRowToNewRow.end()) {
             // If the original row index is not found in the map, update the
             // stmt_sequence attribute to the 'invalid offset' magic value.
-            StmtSeq.set(UINT64_MAX);
+            StmtSeq.set(InvalidOffset);
             continue;
           }
 

llvm/lib/DebugInfo/GSYM/DwarfTransformer.cpp

@@ -320,12 +320,16 @@ static void convertFunctionLineTable(OutputAggregator &Out, CUInfo &CUI,
   // Attempt to retrieve DW_AT_LLVM_stmt_sequence if present.
   std::optional<uint64_t> StmtSeqOffset;
   if (auto StmtSeqAttr = Die.find(llvm::dwarf::DW_AT_LLVM_stmt_sequence)) {
-    // The `DW_AT_LLVM_stmt_sequence` attribute might be set to `UINT64_MAX`
-    // when it refers to an empty line sequence. In such cases, the DWARF linker
-    // will exclude the empty sequence from the final output and assign
-    // `UINT64_MAX` to the `DW_AT_LLVM_stmt_sequence` attribute.
-    uint64_t StmtSeqVal = dwarf::toSectionOffset(StmtSeqAttr, UINT64_MAX);
-    if (StmtSeqVal != UINT64_MAX)
+    // The `DW_AT_LLVM_stmt_sequence` attribute might be set to an invalid
+    // sentinel value when it refers to an empty line sequence. In such cases,
+    // the DWARF linker will exclude the empty sequence from the final output
+    // and assign the sentinel value to the `DW_AT_LLVM_stmt_sequence`
+    // attribute. The sentinel value is UINT32_MAX for DWARF32 and UINT64_MAX
+    // for DWARF64.
+    const uint64_t InvalidOffset =
+        Die.getDwarfUnit()->getFormParams().getDwarfMaxOffset();
+    uint64_t StmtSeqVal = dwarf::toSectionOffset(StmtSeqAttr, InvalidOffset);
+    if (StmtSeqVal != InvalidOffset)
       StmtSeqOffset = StmtSeqVal;
   }