----- On Jan 24, 2022, at 2:42 AM, Linus Torvalds torvalds@linux-foundation.org wrote:
On Sun, Jan 23, 2022 at 9:32 PM Mathieu Desnoyers mathieu.desnoyers@efficios.com wrote:
The rseq rseq_cs.ptr.{ptr32,padding} uapi endianness handling is entirely wrong on 32-bit little endian: a preprocessor logic mistake wrongly uses the big endian field layout on 32-bit little endian architectures.
Fortunately, those ptr32 accessors were never used within the kernel, and only meant as a convenience for user-space.
Please don't double down on something that was already broken once.
Just remove the broken 32-bit one entirely that the kernel doesn't even use, and make everybody use
__u64 ptr64;
and be done with it.
OK, should I just leave:
struct rseq { [...] union rseq_cs { __u64 ptr64; } rseq_cs; [...] };
and remove all the other content from the union, so users of rseq_abi->rseq_cs.ptr64 will continue to work as-is with either old and new headers ? This keeps a union in place with a single element, so I just want to confirm with you that is what you have in mind.
It does make tons of sense to just remove the broken convenience code and let user-space handle this based on the ptr64 field, so it will work fine with old and new headers.
Thanks for your feedback, and travel safe!
Mathieu