[DebugInfo] Make incorrect debug line extended opcode length non-fatal

It is possible to try to keep parsing a debug line program even when the
length of an extended opcode does not match what is expected for that
opcode. This patch changes what was previously a fatal error to be
non-fatal. The parser now continues by assuming the the claimed length
is correct, even if it means moving the offset backwards.

Reviewed by: dblaikie

Differential Revision: https://reviews.llvm.org/D72155

1 files changed, 12 insertions, 7 deletions

diff --git a/llvm/lib/DebugInfo/DWARF/DWARFDebugLine.cpp b/llvm/lib/DebugInfo/DWARF/DWARFDebugLine.cpp
index 2eceadb..b97753e 100644
--- a/llvm/lib/DebugInfo/DWARF/DWARFDebugLine.cpp
+++ b/llvm/lib/DebugInfo/DWARF/DWARFDebugLine.cpp
@@ -685,13 +685,18 @@ Error DWARFDebugLine::LineTable::parse(
         (*OffsetPtr) += Len - 1;
         break;
       }
-      // Make sure the stated and parsed lengths are the same.
-      // Otherwise we have an unparseable line-number program.
-      if (*OffsetPtr - ExtOffset != Len)
-        return createStringError(errc::illegal_byte_sequence,
-                           "unexpected line op length at offset 0x%8.8" PRIx64
-                           " expected 0x%2.2" PRIx64 " found 0x%2.2" PRIx64,
-                           ExtOffset, Len, *OffsetPtr - ExtOffset);
+      // Make sure the length as recorded in the table and the standard length
+      // for the opcode match. If they don't, continue from the end as claimed
+      // by the table.
+      uint64_t End = ExtOffset + Len;
+      if (*OffsetPtr != End) {
+        RecoverableErrorCallback(createStringError(
+            errc::illegal_byte_sequence,
+            "unexpected line op length at offset 0x%8.8" PRIx64
+            " expected 0x%2.2" PRIx64 " found 0x%2.2" PRIx64,
+            ExtOffset, Len, *OffsetPtr - ExtOffset));
+        *OffsetPtr = End;
+      }
     } else if (Opcode < Prologue.OpcodeBase) {
       if (OS)
         *OS << LNStandardString(Opcode);