From: Peter Zijlstra <peterz@infradead.org>
To: Andy Lutomirski <luto@kernel.org>
Cc: the arch/x86 maintainers <x86@kernel.org>,
Josh Poimboeuf <jpoimboe@redhat.com>,
Brian Gerst <brgerst@gmail.com>,
Lai Jiangshan <jiangshanlai@gmail.com>,
Andrew Cooper <Andrew.Cooper3@citrix.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/2] x86,entry: Use PUSH_AND_CLEAR_REGS for compat
Date: Wed, 20 Apr 2022 16:51:37 +0200 [thread overview]
Message-ID: <20220420145137.GG2731@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <ed167304-0d43-42fb-9da1-1358dded3a2f@www.fastmail.com>
On Wed, Apr 20, 2022 at 07:26:54AM -0700, Andy Lutomirski wrote:
>
>
> On Tue, Apr 19, 2022, at 1:41 PM, Peter Zijlstra wrote:
> > Since the upper regs don't exist for ia32 code, preserving them
> > doesn't hurt and it simplifies the code.
>
> They exist for compat code, though, and should be preserved for ABI
> purposes. Programs that do int $0x80 in 64-bit code do exist.
So this patch preserves semantics for int80, it changes things for
sysenter/syscall, those currently clear the high registers, whereas
after this patch they behave identical to int80.
So the earlier patch:
https://lkml.kernel.org/r/20220408223827.GR2731@worktop.programming.kicks-ass.net
preserves semantics across the board but is slightly more complicated.
And as argued elsewhere in thie thread; if preserving instead of
clearing the high regs is a valid attach surface, then int80 already
provides it, so I don't see how doing the same to sys* is any worse.
prev parent reply other threads:[~2022-04-20 14:51 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-19 20:41 [PATCH 0/2] x86: A few random cleanups Peter Zijlstra
2022-04-19 20:41 ` [PATCH 1/2] x86: Simplify Retpoline thunk Peter Zijlstra
2022-04-20 15:27 ` Josh Poimboeuf
2022-04-20 15:51 ` Peter Zijlstra
2022-04-20 16:01 ` Josh Poimboeuf
2022-04-19 20:41 ` [PATCH 2/2] x86,entry: Use PUSH_AND_CLEAR_REGS for compat Peter Zijlstra
2022-04-20 3:21 ` Josh Poimboeuf
2022-04-20 7:07 ` Peter Zijlstra
2022-04-20 14:58 ` Josh Poimboeuf
2022-04-20 4:29 ` Lai Jiangshan
2022-04-20 14:26 ` Andy Lutomirski
2022-04-20 14:51 ` Peter Zijlstra [this message]
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