linux-kernel - Re: [REGRESSION] x86/entry: TIF_SINGLESTEP handling is still broken

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Date:   Sun, 31 Jan 2021 14:04:44 -0800
From:   Andy Lutomirski <luto@...capital.net>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Kyle Huey <me@...ehuey.com>, Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Gabriel Krisman Bertazi <krisman@...labora.com>,
        open list <linux-kernel@...r.kernel.org>,
        Robert O'Callahan <rocallahan@...il.com>
Subject: Re: [REGRESSION] x86/entry: TIF_SINGLESTEP handling is still broken



> On Jan 31, 2021, at 1:30 PM, Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> 
> Btw Kyle, do you have a good simple test-case for this? Clearly this
> is some weird special case use, and regular single-stepping works
> fine.
> 
> 

Indeed, and I have tests for this.

TBH, the TIF_SINGLESTEP code makes no sense, and I think it has at least three overloaded meanings. I can try to look in a bit.  I’ve mostly avoided breaking it in the past, but that doesn’t mean I understand the original intent.