Re: [PATCH 7/3] signal: Deliver all of the perf_data in si_perf

[Peter Zijlstra]

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.