[PATCH] D116511: [clang-cl] Support the /HOTPATCH flag

[Alexandre Ganea via Phabricator via cfe-commits]

aganea created this revision.
aganea added reviewers: amccarth, craig.topper, hans, rnk, stefan_reinalter.
Herald added subscribers: ormris, dexonsmith, dang, pengfei, hiraditya.
aganea requested review of this revision.
Herald added projects: clang, LLVM.
Herald added subscribers: llvm-commits, cfe-commits.

This patch adds support for the /HOTPATCH flag: https://docs.microsoft.com/sv-se/cpp/build/reference/hotpatch-create-hotpatchable-image?view=msvc-170&viewFallbackFrom=vs-2019

The flag is translated to a new `-fhotpatch` cc1 flag, which in turn adds a `patchable-function` attribute for each function in the TU. This is then picked up by the `PatchableFunction` pass which would generate a `TargetOpcode::PATCHABLE_OP` of minsize = 2 (which means the target instruction must resolve to at least two bytes). Currently `TargetOpcode::PATCHABLE_OP` is only implemented for x86/x64.

Additionally we generate a 'hot patchable' flag in the CodeView debug stream, in the `S_COMPILE3` record. This flag is then picked up by LLD (or link.exe) and is used in conjunction with the linker `/FUNCTIONPADMIN` flag to generate extraneous space before each function, to accommodate for live patching. Please see: https://github.com/llvm/llvm-project/blob/d703b922961e0d02a5effdd4bfbb23ad50a3cc9f/lld/COFF/Writer.cpp#L1298

The end result is that one can finally use Live++ <https://molecular-matters.com/> or Recode <http://www.indefiant.com/> along with clang-cl.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D116511

Files:
  clang/include/clang/Basic/CodeGenOptions.def
  clang/include/clang/Driver/Options.td
  clang/lib/CodeGen/BackendUtil.cpp
  clang/lib/CodeGen/CodeGenFunction.cpp
  clang/lib/Driver/ToolChains/Clang.cpp
  clang/test/CodeGen/patchable-function-entry.c
  clang/test/CodeGenCXX/debug-info-hotpatch.cpp
  clang/test/Driver/cl-options.c
  llvm/include/llvm/Target/TargetOptions.h
  llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp

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