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

[Eric W. Biederman]

Peter Zijlstra <peterz@xxxxxxxxxxxxx> writes:

> 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.

I see why it is fine to truncate the data field into an unsigned long.

Other than technical difficulties in extending siginfo_t is there any
reason not to define data as a __u64?

Eric