On Sun, May 02, 2021 at 01:39:16PM -0500, Eric W. Biederman wrote:

The one thing that this doesn't do is give you a 64bit field
on 32bit architectures.

On 32bit builds the layout is:

	int si_signo;
	int si_errno;
	int si_code;
	void __user *_addr;
        
So I believe if the first 3 fields were moved into the _sifields union
si_perf could define a 64bit field as it's first member and it would not
break anything else.

Given that the data field is 64bit that seems desirable.

The data field is fundamentally an address, it is internally a u64
because the perf ring buffer has u64 alignment and it saves on compat
crap etc.

So for the 32bit/compat case the high bits will always be 0 and
truncating into an unsigned long is fine.