DWARF: Properly emit signed 32 bit values for advance_line (#2625)

The LLVM SData field is 64-bit (to support 64-bit
addresses I suppose) so when we assigned to it we
actually led it to emit an LEB for a signed 64-bit value
that is an unsigned 32-bit one. This worked in LLVM
(where I guess it forces the value to 32-bit anyhow?)
but failed in gimli (where I guess it doesn't?).

1 files changed, 4 insertions, 1 deletions

diff --git a/src/wasm/wasm-debug.cpp b/src/wasm/wasm-debug.cpp
index c4d403e64..73e473f9a 100644
--- a/src/wasm/wasm-debug.cpp
+++ b/src/wasm/wasm-debug.cpp
@@ -261,7 +261,10 @@ struct LineState {
     }
     if (line != old.line && !useSpecial) {
       auto item = makeItem(llvm::dwarf::DW_LNS_advance_line);
-      item.SData = line - old.line;
+      // In wasm32 we have 32-bit addresses, and the delta here might be
+      // negative (note that SData is 64-bit, as LLVM supports 64-bit
+      // addresses too).
+      item.SData = int32_t(line - old.line);
       newOpcodes.push_back(item);
     }
     if (col != old.col) {