[build] relax function type cast error

[kmemarian]

The previously used -Wcast-function-type also enables -Wcast-function-type-strict on recent versions of Clang. This does not like casts turning function parameter types to void * (which happens throughout cn-smt/). This stricter check is only relevant when using CFI.

[kmemarian]

:-(, gcc doesn't know that flag (and now I realised probably neither do older clangs). Not sure what is the best approach to make every compilers happy then.

[msaljuk]

:-(, gcc doesn't know that flag (and now I realised probably neither do older clangs). Not sure what is the best approach to make every compilers happy then.

I was running into this too. Short of rewriting the code to not cast to void ptrs, would it be feasible to relax -Wcast-function-type just around the offending callsites with a #pragma GCC diagnostic ignored?

[pqwy]

We can delete -Wcast-function-type and work from there.

The warning comes from adding a subset of what Linux uses to the build. As it is, various warnings still need to be turned off when compiling as part of Linux, so enforcing this particular one does not improve things drastically.

[dc-mak]

what about a clang pragma aroud the offending code? https://stackoverflow.com/questions/48426484/concise-way-to-disable-specific-warning-instances-in-clang

there might be a way to do so for only specific versions of clang if the pragma is not backwards compatible

[dc-mak]

E.g. something like this (not tested, just a suggestion).

#if defined(__clang__)
#  if __has_warning("-Wcast-function-type-strict")
#    pragma clang diagnostic push
#    pragma clang diagnostic ignored "-Wcast-function-type-strict"
#  endif
#endif

/* cast that triggers the warning */

#if defined(__clang__)
#  if __has_warning("-Wcast-function-type-strict")
#    pragma clang diagnostic pop
#  endif
#endif