[all-commits] [llvm/llvm-project] e68a03: [libc] fix -Wcast-function-type via union rather t...

[Nick Desaulniers via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: e68a0320a1592bf408ac6458efa2d1c548cfed7a
      https://github.com/llvm/llvm-project/commit/e68a0320a1592bf408ac6458efa2d1c548cfed7a
  Author: Nick Desaulniers <nickdesaulniers at users.noreply.github.com>
  Date:   2024-01-03 (Wed, 03 Jan 2024)

  Changed paths:
    M libc/src/signal/linux/signal_utils.h

  Log Message:
  -----------
  [libc] fix -Wcast-function-type via union rather than reinterpret_cast (#76875)

The GCC build is producing the following diagnostic:

llvm-project/libc/src/signal/linux/signal_utils.h: In member function
    ‘__llvm_libc_18_0_0_git::KernelSigaction&
__llvm_libc_18_0_0_git::KernelSigaction::operator=(const sigaction&)’:
    llvm-project/libc/src/signal/linux/signal_utils.h:38:20: warning:
cast between incompatible function types from ‘void (*)(int, siginfo_t*,
    void*)’ to ‘void (*)(int)’ [-Wcast-function-type]
38 | sa_handler = reinterpret_cast<HandlerType *>(sa.sa_sigaction);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
llvm-project/libc/src/signal/linux/signal_utils.h: In member function
‘__llvm_libc_18_0_0_git::KernelSigaction::operator sigaction() const’:
    llvm-project/libc/src/signal/linux/signal_utils.h:51:25: warning:
cast between incompatible function types from ‘void (*)(int)’ to ‘void
    (*)(int, siginfo_t*, void*)’ [-Wcast-function-type]
51 | sa.sa_sigaction = reinterpret_cast<SiginfoHandlerType
*>(sa_handler);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Two issues here:
1. Clang supports -Wcast-function-type, but not as part of the -Wextra
group.
2. The existing implementation tried to work around the oddity that is
the
kernel's struct sigaction != POSIX via reinterpret_cast in a way that's
not
compatible with -Wcast-function-type. Just use a union which is well
defined
(and two function pointers are the same size.)

Link: https://github.com/llvm/llvm-project/issues/76872

Fixes: https://github.com/llvm/llvm-project/issues/74617