[all-commits] [llvm/llvm-project] 5dc8aa: [llvm][IR] Add no_cfi constant

[Sami Tolvanen via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 5dc8aaac39c53c8e91842a9233921759544759bc
      https://github.com/llvm/llvm-project/commit/5dc8aaac39c53c8e91842a9233921759544759bc
  Author: Sami Tolvanen <samitolvanen at google.com>
  Date:   2021-12-20 (Mon, 20 Dec 2021)

  Changed paths:
    M llvm/docs/LangRef.rst
    M llvm/include/llvm/AsmParser/LLParser.h
    M llvm/include/llvm/AsmParser/LLToken.h
    M llvm/include/llvm/Bitcode/LLVMBitCodes.h
    M llvm/include/llvm/IR/Constants.h
    M llvm/include/llvm/IR/Value.def
    M llvm/lib/AsmParser/LLLexer.cpp
    M llvm/lib/AsmParser/LLParser.cpp
    M llvm/lib/Bitcode/Reader/BitcodeAnalyzer.cpp
    M llvm/lib/Bitcode/Reader/BitcodeReader.cpp
    M llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
    M llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
    M llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
    M llvm/lib/IR/AsmWriter.cpp
    M llvm/lib/IR/Constants.cpp
    M llvm/lib/IR/LLVMContextImpl.h
    M llvm/lib/Transforms/IPO/LowerTypeTests.cpp
    M llvm/lib/Transforms/Utils/ValueMapper.cpp
    A llvm/test/Bitcode/nocfivalue.ll
    A llvm/test/CodeGen/X86/nocfivalue.ll
    A llvm/test/Transforms/LowerTypeTests/nocfivalue.ll
    M llvm/utils/emacs/llvm-mode.el
    M llvm/utils/vim/syntax/llvm.vim

  Log Message:
  -----------
  [llvm][IR] Add no_cfi constant

With Control-Flow Integrity (CFI), the LowerTypeTests pass replaces
function references with CFI jump table references, which is a problem
for low-level code that needs the address of the actual function body.

For example, in the Linux kernel, the code that sets up interrupt
handlers needs to take the address of the interrupt handler function
instead of the CFI jump table, as the jump table may not even be mapped
into memory when an interrupt is triggered.

This change adds the no_cfi constant type, which wraps function
references in a value that LowerTypeTestsModule::replaceCfiUses does not
replace.

Link: https://github.com/ClangBuiltLinux/linux/issues/1353

Reviewed By: nickdesaulniers, pcc

Differential Revision: https://reviews.llvm.org/D108478


  Commit: ec2e26eaf63558934f5b73a6e530edc453cf9508
      https://github.com/llvm/llvm-project/commit/ec2e26eaf63558934f5b73a6e530edc453cf9508
  Author: Sami Tolvanen <samitolvanen at google.com>
  Date:   2021-12-20 (Mon, 20 Dec 2021)

  Changed paths:
    M clang/docs/LanguageExtensions.rst
    M clang/include/clang/AST/Expr.h
    M clang/include/clang/Basic/Builtins.def
    M clang/include/clang/Basic/DiagnosticSemaKinds.td
    M clang/lib/AST/Expr.cpp
    M clang/lib/AST/ExprConstant.cpp
    M clang/lib/CodeGen/CGBuiltin.cpp
    M clang/lib/CodeGen/CGExprConstant.cpp
    M clang/lib/CodeGen/CodeGenModule.cpp
    M clang/lib/CodeGen/CodeGenModule.h
    M clang/lib/Sema/SemaChecking.cpp
    M clang/lib/StaticAnalyzer/Checkers/BuiltinFunctionChecker.cpp
    A clang/test/CodeGen/builtin-function-start.cpp
    M clang/test/SemaCXX/builtins.cpp

  Log Message:
  -----------
  [Clang] Add __builtin_function_start

Control-Flow Integrity (CFI) replaces references to address-taken
functions with pointers to the CFI jump table. This is a problem
for low-level code, such as operating system kernels, which may
need the address of an actual function body without the jump table
indirection.

This change adds the __builtin_function_start() builtin, which
accepts an argument that can be constant-evaluated to a function,
and returns the address of the function body.

Link: https://github.com/ClangBuiltLinux/linux/issues/1353

Depends on D108478

Reviewed By: pcc, rjmccall

Differential Revision: https://reviews.llvm.org/D108479


Compare: https://github.com/llvm/llvm-project/compare/02b6fb218e44...ec2e26eaf635