linux-kernel - Re: [PATCH] riscv: eliminate unreliable __builtin_frame

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Date:   Wed, 19 Jan 2022 22:07:39 +0100
From:   Andreas Schwab <schwab@...ux-m68k.org>
To:     Jessica Clarke <jrtc27@...c27.com>
Cc:     Changbin Du <changbin.du@...il.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] riscv: eliminate unreliable __builtin_frame_address(1)

On Jan 19 2022, Jessica Clarke wrote:

> My point is that the only thing that can possibly read the incoming
> frame pointer of a leaf function is the leaf function itself, and since
> it knows where it’s putting it then there is no ABI issue, it just
> remembers where it put it and loads it from there.

llvm sidesteps that issue by always saving ra when creating a frame,
even in a leaf function, so it can use a constant offset.

-- 
Andreas Schwab, schwab@...ux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
"And now for something completely different."