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From: "Roger Pau Monné" <roger.pau@citrix.com>
To: Jan Beulich <jbeulich@suse.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>, Wei Liu <wl@xen.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	Ross Lagerwall <ross.lagerwall@citrix.com>,
	Xen-devel <xen-devel@lists.xenproject.org>
Subject: Re: [PATCH 2/3] x86/entry: Make #PF/NMI/INT0x82 more amenable to livepatching
Date: Wed, 24 Jan 2024 10:22:46 +0100	[thread overview]
Message-ID: <ZbDW5nCuHW7xCYOo@macbook> (raw)
In-Reply-To: <ebdfc495-b8bc-4468-8b41-d5fdb2a85adb@suse.com>

On Tue, Jan 23, 2024 at 02:43:15PM +0100, Jan Beulich wrote:
> On 23.01.2024 14:37, Roger Pau Monné wrote:
> > On Tue, Jan 23, 2024 at 10:22:10AM +0100, Jan Beulich wrote:
> >> On 22.01.2024 19:17, Andrew Cooper wrote:
> >>> It is bad form to have inter-function fallthrough.  It only functions right
> >>> now because alignment padding bytes are NOPs.
> >>
> >> But that's a requirement anyway in executable sections.
> > 
> > Really?  I was under the impression we wanted to replace the padding
> > nops with rets maybe, or even poison the padding with int3 or ud2.
> 
> Well, that would be a decision of ours. Which then imo can't be described as
> "only functions right now because ..." The assembler can't[1] use other than
> NOPs by default, as it can't know whether fall-through is intended.

So it's not a strict requirement of ELF that padding is done using
nops, it's just the default decision of the assembler because it
doesn't know better.

Thanks, Roger.


  reply	other threads:[~2024-01-24  9:22 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-01-22 18:17 [PATCH 0/3] x86/entry: ELF fixes and improvments Andrew Cooper
2024-01-22 18:17 ` [PATCH 1/3] x86/entry: Fix ELF metadata for NMI and handle_ist_exception Andrew Cooper
2024-01-23  9:10   ` Jan Beulich
2024-01-22 18:17 ` [PATCH 2/3] x86/entry: Make #PF/NMI/INT0x82 more amenable to livepatching Andrew Cooper
2024-01-23  9:22   ` Jan Beulich
2024-01-23 13:37     ` Roger Pau Monné
2024-01-23 13:43       ` Jan Beulich
2024-01-24  9:22         ` Roger Pau Monné [this message]
2024-01-22 18:17 ` [PATCH 2/3] x86/entry: Make #PF/NMI " Andrew Cooper
2024-01-22 18:34   ` Andrew Cooper
2024-01-22 18:17 ` [PATCH 3/3] x86/entry: Make intra-funciton symbols properly local Andrew Cooper
2024-01-23  9:35   ` Jan Beulich
2024-01-24  9:21   ` Roger Pau Monné

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