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Message-ID: <1fcb00f4-f8b0-4c98-88d5-16895066d222@rivosinc.com>
Date: Thu, 14 Sep 2023 19:32:35 +0200
From: Clément Léger <cleger@...osinc.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Masami Hiramatsu <mhiramat@...nel.org>,
linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
Beau Belgrave <beaub@...ux.microsoft.com>
Subject: Re: [PATCH] tracing/user_events: align uaddr on unsigned long
alignment
On 14/09/2023 19:29, Steven Rostedt wrote:
> On Thu, 14 Sep 2023 13:17:00 -0400
> Steven Rostedt <rostedt@...dmis.org> 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);
> }
Hi Steven,
Nice catch ! I don't have big endian at end but I'll check that.
Thanks,
>
> -- Steve
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