linux-kernel - Re: [PATCH v2 2/4] usb: typec: tps6598x: Add trace event for status register

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Message-ID: <c48e4250-a42a-9f99-1280-69b0b5cfb69d@ramsayjones.plus.com>
Date:   Sun, 14 Feb 2021 19:31:37 +0000
From:   Ramsay Jones <ramsay@...sayjones.plus.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-usb@...r.kernel.org
Cc:     Guido Günther <agx@...xcpu.org>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        Sparse Mailing-list <linux-sparse@...r.kernel.org>
Subject: Re: [PATCH v2 2/4] usb: typec: tps6598x: Add trace event for status
 register



On 14/02/2021 19:00, Linus Torvalds wrote:
> On Sun, Feb 14, 2021 at 10:42 AM Ramsay Jones
> <ramsay@...sayjones.plus.com> wrote:
>>
>>>
>>> I looked around but didn't find any hints how to fix this. Any pointers
>>> I missed (added the sparse list to cc:)?
>>
>> This is a limitation of sparse; when using the 'stringize' pre-processor
>> operator #, the maximum size of the resulting string is about 8k (if I
>> remember correctly).
> 
> Well, yes and no.
> 
> The C89 standard actually says that a string literal can be at most
> 509 characters to be portable. C99 increased it to 4095 characters.
> 
> Sparse makes the limit higher, and the limit could easily be expanded
> way past 8kB - but the point is that large string literals are
> actually not guaranteed to be valid C.
> 
> So honestly, it really sounds like that TRACE_EVENT() thing is doing
> something it shouldn't be doing.

Yep, as I said, I didn't submit the patch - rather I changed the source
so as not to need such a long string.

> I don't think there's any fundamental limit why sparse does 8kB as a
> limit (just a few random buffers). Making sparse accept larger ones
> should be as simple as just increasing MAX_STRING, but I really don't
> think the kernel should encourage that kind of excessive string sizes.

I agree, but I wiggled my patch (which doesn't increase MAX_STRING) to
apply to the current codebase, and ... it now fails two tests! ;-)
(It seems, in the intervening 9 years, the show_token_sequence() function
fixed the quoting of double-quotes in the resulting strings, which
my patch fails to do).

Sorry for the noise.

ATB,
Ramsay Jones