GH-130673: Gracefully handle missing sections in JIT build (GH-130906)

Author: rennsax

Misc/NEWS.d/next/Build/2025-03-06-20-55-34.gh-issue-130673.T3RSCI.rst

@@ -0,0 +1,2 @@
+Fix potential ``KeyError`` when handling object sections during JIT building
+process.

Tools/jit/_targets.py

@@ -323,7 +323,11 @@ def _handle_section(
         if section_type == "SHT_RELA":
             assert "SHF_INFO_LINK" in flags, flags
             assert not section["Symbols"]
-            value, base = group.symbols[section["Info"]]
+            maybe_symbol = group.symbols.get(section["Info"])
+            if maybe_symbol is None:
+                # These are relocations for a section we're not emitting. Skip:
+                return
+            value, base = maybe_symbol
             if value is _stencils.HoleValue.CODE:
                 stencil = group.code
             else: