linux-kernel - Re: [PATCH v5 12/20] vsprintf: add new `%pA` format specifier

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Date:   Fri, 18 Mar 2022 16:07:31 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Miguel Ojeda <ojeda@...nel.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org,
        Gary Guo <gary@...yguo.net>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Wedson Almeida Filho <wedsonaf@...gle.com>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: Re: [PATCH v5 12/20] vsprintf: add new `%pA` format specifier

On Thu, Mar 17, 2022 at 07:10:00PM +0100, Miguel Ojeda wrote:
> From: Gary Guo <gary@...yguo.net>
> 
> This patch adds a format specifier `%pA` to `vsprintf` which formats
> a pointer as `core::fmt::Arguments`. Doing so allows us to directly
> format to the internal buffer of `printf`, so we do not have to use
> a temporary buffer on the stack to pre-assemble the message on
> the Rust side.
> 
> This specifier is intended only to be used from Rust and not for C, so
> `checkpatch.pl` is intentionally unchanged to catch any misuse.

...

> +	case 'A':
> +		if (!IS_ENABLED(CONFIG_RUST)) {
> +			WARN_ONCE(1, "Please remove %%pA from non-Rust code\n");
> +			return error_string(buf, end, "(%pA?)", spec);
> +		}

I'm wondering if the Big Scary Banner as trace_printk() does would be better
(in case we can tell that %pA is used in the code when RUST=n).

-- 
With Best Regards,
Andy Shevchenko