Re: offsetof() backports for clang-16+

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Sun, Jan 15, 2023 at 09:46:36PM -0700, Nathan Chancellor wrote:
> Hi Greg and Sasha,
> 
> Clang 16 (current main, next major release) errors when offsetof() has a
> type defintion in it, in response to language in newer C standards
> stating it is undefined behavior.
> 
> https://github.com/llvm/llvm-project/commit/e327b52766ed497e4779f4e652b9ad237dfda8e6
> https://reviews.llvm.org/D133574
> 
> While this might be eventually demoted to just a warning, the kernel has
> already cleaned up places that had this construct, so we can apply them
> to the stable trees and avoid the issue altogether.
> 
> Please find attached mbox files for all supported stable trees, which
> fix up the relevant instances for each tree using the upstream commits:
> 
> 55228db2697c ("x86/fpu: Use _Alignof to avoid undefined behavior in TYPE_ALIGN")
> 09794a5a6c34 ("tracing: Use alignof__(struct {type b;}) instead of offsetof()")
> 
> The fpu commit uses _Alignof, which as far as I can tell was only
> supported in GCC 4.7.0+. This is not a problem for mainline due to
> requiring GCC 5.1.0+ but it could be relevant for old trees like 4.14,
> which have an older minimum supported version. I hope people are not
> using ancient compilers like that but I suppose if they are using 4.14,
> they might just be stuck with old software...
> 
> If there are any issues or comments, please let me know.

Now queued up, thanks.

greg k-h