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Add new rustc_panic_abort_runtime attribute for libpanic_abort #66489

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Add new rustc_panic_abort_runtime attribute for libpanic_abort #66489

wants to merge 2 commits into from

Commits on Dec 21, 2019

  1. Add new rustc_panic_abort_runtime attribute for libpanic_abort 

    Supersedes rust-lang#66311

This replaces the hack in `bootstrap`, allowing the special handling for
`libpanic_abort` to be encoded into the crate source itself, rather than
existing as special knowledge in the build system. This will allow Miri
(and any other users of Xargo) to correctly build `libpanic_abort`
without relying on `bootstrap` or custom wrapepr hacks.

The trickeist part of this PR is how we handle LLVM. The `emscripten`
target family requires the "-enable-emscripten-cxx-exceptions" flag
to be passed to LLVM when the panic strategy is set to "unwind".

Unfortunately, the location of this emscripten-specific check ends up
creating a circular dependency between LLVM and attribute resoltion.
When we check the panic strategy, we need to have already parsed crate
attributes, so that we determine if `rustc_panic_abort_runtime` was set.
However, attribute parsing requires LLVM to be initialized, so that we
can proerly handle cfg-gating of target-specific features. However, the
whole point of checking the panic strategy is to determinne which flags
to use during LLVM initialization!

To break this circular dependency, we explicitly set the
"-enable-emscripten-cxx-exceptions" in LLVM's argument-parsing framework
(using public but poorly-documented APIs). While this approach is
unfortunate, it only affects emscripten, and only modifies a
command-line flag which is never used until much later (when we create a
`PassManager`).
    @Aaron1011
    Aaron1011 committed Dec 21, 2019
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  2. Fix typos 

    Co-Authored-By: Thomas Lively <7121787+tlively@users.noreply.github.com>
    @Aaron1011 @tlively
    Aaron1011 and tlively committed Dec 21, 2019
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