Commits on Nov 5, 2023

1. [LLD] [COFF] Error out if new LTO objects are pulled in after the mai… …

   …n LTO compilation
   
   Normally, this shouldn't happen. It can happen in exceptional
   circumstances, if the compiled output of a bitcode object file
   references symbols that weren't listed as undefined in the bitcode
   object file itself.
   
   This can at least happen in the following cases:
   - A custom SEH personality is set via asm()
   - Compiler generated calls to builtin helper functions, such as
     __chkstk, or __rt_sdiv on arm
   
   Both of these produce undefined references to symbols after
   compiling to a regular object file, that aren't visible on the
   level of the IR object file.
   
   This is only an issue if the referenced symbols are provided as
   LTO objects themselves; loading regular object files after the
   LTO compilation works fine.
   
   Custom SEH personalities are rare, but one CRT startup file in
   mingw-w64 does this. The referenced pesonality function is usually
   provided via an import library, but for WinStore targets, a local
   dummy reimplementation in C is used, which can be an LTO object.
   
   Generated calls to builtins is very common, but the builtins aren't
   usually provided as LTO objects (compiler-rt's builtins explicitly
   pass -fno-lto when building), and many of the builtins are provided
   as raw .S assembly files, which don't get built as LTO objects
   anyway, even if built with -flto.
   
   If hitting this unusual, but possible, situation, error out cleanly
   with a clear message rather than crashing.

   

   mstorsjo committed Nov 5, 2023
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