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[ASan] Introduce a way set different ways of emitting module destructors.

Authored by delcypher on Feb 9 2021, 5:01 PM.

Description

[ASan] Introduce a way set different ways of emitting module destructors.

Previously there was no way to control how module destructors were emitted
by ModuleAddressSanitizerPass. However, we want language frontends (e.g. Clang)
to be able to decide how to emit these destructors (if at all).

This patch introduces the AsanDtorKind enum that represents the different ways
destructors can be emitted. There are currently only two valid ways to emit destructors.

  • Global - Use llvm.global_dtors. This was the previous behavior and is the default.
  • None - Do not emit module destructors.

The ModuleAddressSanitizerPass and the various wrappers around it have been updated
to take the AsanDtorKind as an argument.

The -asan-destructor-kind= command line argument has been introduced to make this
easy to test from opt. If this argument is specified it overrides the value passed
to the ModuleAddressSanitizerPass constructor.

Note that AsanDtorKind is not bool because we will introduce a new way to
emit destructors in a subsequent patch.

Note that AsanDtorKind is given its own header file because if it is declared
in Transforms/Instrumentation/AddressSanitizer.h it leads to compile error
(Module is ambiguous) when trying to use it in
clang/Basic/CodeGenOptions.def.

rdar://71609176

Differential Revision: https://reviews.llvm.org/D96571

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