linux-kernel - Re: [PATCH] lockdep: avoid struct return in lock

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Message-ID: <aFJL7GW_mdX-VZIR@Mac.home>
Date: Tue, 17 Jun 2025 22:17:32 -0700
From: Boqun Feng <boqun.feng@...il.com>
To: Arnd Bergmann <arnd@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
	Will Deacon <will@...nel.org>,
	Nathan Chancellor <nathan@...nel.org>,
	Arnd Bergmann <arnd@...db.de>, Waiman Long <longman@...hat.com>,
	Nick Desaulniers <nick.desaulniers+lkml@...il.com>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	Kent Overstreet <kent.overstreet@...ux.dev>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH] lockdep: avoid struct return in lock_stats()

On Tue, Jun 10, 2025 at 11:29:21AM +0200, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> Returning a large structure from the lock_stats() function causes clang
> to have multiple copies of it on the stack and copy between them, which
> can end up exceeding the frame size warning limit:
> 
> kernel/locking/lockdep.c:300:25: error: stack frame size (1464) exceeds limit (1280) in 'lock_stats' [-Werror,-Wframe-larger-than]
>   300 | struct lock_class_stats lock_stats(struct lock_class *class)
> 
> Change the calling conventions to directly operate on the caller's copy,
> which apparently is what gcc does already.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Queued for more tests and reviews, thanks!

Regards,
Boqun