Re: [PATCH] tracing/user_events: align uaddr on unsigned long alignment

[Steven Rostedt]

On Thu, 14 Sep 2023 13:17:00 -0400
Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:

> Now lets look at big endian layout:
> 
>  uaddr = 0xbeef0004
>  enabler = 1;
> 
>  memory at 0xbeef0000:  00 00 00 00 00 00 00 02
>                                     ^
>                                     addr: 0xbeef0004
> 
> 				(enabler is set )
> 
> 	bitoffset = uaddr & (sizeof(unsigned long) - 1); bitoffset = 4
> 	bit_offset *= 8;				 bitoffset = 32
> 	uaddr &= ~(sizeof(unsigned long) - 1);		 uaddr = 0xbeef0000
> 
> 	ptr = kaddr + (uaddr & ~PAGE_MASK);
> 
> 	clear_bit(1 + 32, ptr);
> 
>  memory at 0xbeef0000:  00 00 00 00 00 00 00 02
>                                   ^
> 				bit 33 of 0xbeef0000
> 
> I don't think that's what you expected!

I believe the above can be fixed with:

	bit_offset = uaddr & (sizeof(unsigned long) - 1);
	if (bit_offset) {
#ifdef CONFIG_CPU_BIG_ENDIAN
		bit_offest = 0;
#else
		bit_offset *= BITS_PER_BYTE;
#endif
		uaddr &= ~(sizeof(unsigned long) - 1);
	}

-- Steve