Commits on Dec 7, 2021

1. Use object crate for .rustc metadata generation …

   We already use the object crate for generating uncompressed .rmeta
   metadata object files. This switches the generation of compressed
   .rustc object files to use the object crate as well. These have
   slightly different requirements in that .rmeta should be completely
   excluded from any final compilation artifacts, while .rustc should
   be part of shared objects, but not loaded into memory.
   
   The primary motivation for this change is rust-lang#90326: In LLVM 14, the
   current way of setting section flags (and in particular, preventing
   the setting of SHF_ALLOC) will no longer work. There are other ways
   we could work around this, but switching to the object crate seems
   like the most elegant, as we already use it for .rmeta, and as it
   makes this independent of the codegen backend. In particular, we
   don't need separate handling in codegen_llvm and codegen_gcc.
   codegen_cranelift should be able to reuse the implementation as
   well, though I have omitted that here, as it is not based on
   codegen_ssa.
   
   This change mostly extracts the existing code for .rmeta handling
   to allow using it for .rustc as well, and adjust the codegen
   infrastructure to handle the metadata object file separately: We
   no longer create a backend-specific module for it, and directly
   produce the compiled module instead.
   
   This does not fix rust-lang#90326 by itself yet, as .llvmbc will need to be
   handled separately.

   

   nikic committed Dec 7, 2021
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