From: Miroslav Benes <mbenes@suse.cz>
To: Joe Lawrence <joe.lawrence@redhat.com>
Cc: Nicholas Mc Guire <hofrat@osadl.org>,
Josh Poimboeuf <jpoimboe@redhat.com>,
Jessica Yu <jeyu@kernel.org>, Jiri Kosina <jikos@kernel.org>,
Petr Mladek <pmladek@suse.com>,
live-patching@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH V2] livepatch: fix non-static warnings
Date: Tue, 18 Dec 2018 09:49:14 +0100 (CET) [thread overview]
Message-ID: <alpine.LSU.2.21.1812180934090.9644@pobox.suse.cz> (raw)
In-Reply-To: <20ef1d3a-2916-ce00-2938-3397746efac9@redhat.com>
On Mon, 17 Dec 2018, Joe Lawrence wrote:
> On 12/17/2018 07:03 AM, Miroslav Benes wrote:
> > Hi,
> >
> > I'm sorry for being late to the party.
> >
> > On Sun, 16 Dec 2018, Nicholas Mc Guire wrote:
> >
> >> Sparse reported warnings about non-static symbols. For the variables
> >> a simple static attribute is fine - for those symbols referenced by
> >> livepatch via klp_func the symbol-names must be unmodified in the
> >> symbol table - to resolve this the __noclone attribute is used
> >> for the shared statically declared functions.
> >>
> >> Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
> >> Suggested-by: Joe Lawrence <joe.lawrence@redhat.com>
> >> Link: https://lkml.org/lkml/2018/12/13/827
> >
> > A nit, but I'd reorder the tags. Link, Suggested-by:, Signed-off-by:. Also
> > it would be great if you used https://lkml.kernel.org/r/${Msg-ID}
> > redirection.
> >
> >> ---
> >>
> >> V2: not all static functions shared need to carry the __noclone
> >> attribute only those that need to be resolved at runtime by
> >> livepatch - so drop the unnecessary __noclone attributes as
> >> well as the Note on __noclone as suggested by Joe Lawrence
> >> <joe.lawrence@redhat.com> - thanks !
> >
> > I talked to Martin Jambor (GCC) and he suggested __attribute__((used)). It
> > should be better than __noclone, which was reportedly implemented only for
> > testing purposes (which is why it does not imply noinline, although
> > inlining internally uses cloning). Newer gcc also has "noipa" attribute,
> > but "used" would definitely be safe.
> >
> > Sorry for not responding earlier.
> >
>
> Hi Miroslav,
>
> Thanks for following up on this. "noipa" would have been nice to use,
> but as you say, is a newer gcc attribute.
>
> Regarding "used" vs. "noclone", can we assume that "used" implies that
> the function name remains unchanged?
I am not sure. I'd argue that it does imply that, but it could just be
a consequence without any guarantees. My understanding is that gcc cannot
assume about a symbol and its references. So it should be preserved as is.
> The gcc online doc [1] speaks about ensuring that "code must be
> emitted". This reads like it solves our
> static-function-not-directly-referenced problem, but isn't explicit
> about naming.
Correct.
> used
>
> This attribute, attached to a function, means that code must be
> emitted for the function even if it appears that the function is not
> referenced. This is useful, for example, when the function is
> referenced only in inline assembly.
>
> Perhaps it's equivalent to a "I want to keep this function and leave
> it's symbols alone" attribute. FWIW, I modified Nicholas' change on my
> box to use "used" and it worked as Martin advertised, so it would get my
> Ack.
>
> I'm just being picky about its documentation and how we should note its
> usage in the v3 patch. Think that s/__noclone/used/g of the v2 commit
> message would be sufficient?
We could rephrase it. After all it is not only about symbol names in the
symbol table. The traceable/patchable code has to be present...
"Sparse reported warnings about non-static symbols. For the variables
a simple static attribute is fine - for the functions referenced by
livepatch via klp_func the symbol-names must be unmodified in the
symbol table and the patchable code has to be emitted.
Attach __used attribute to the shared statically declared functions."
?
Miroslav
next prev parent reply other threads:[~2018-12-18 8:49 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-16 13:07 [PATCH V2] livepatch: fix non-static warnings Nicholas Mc Guire
2018-12-17 12:03 ` Petr Mladek
2018-12-17 12:03 ` Miroslav Benes
2018-12-17 15:44 ` Joe Lawrence
2018-12-17 19:23 ` Nicholas Mc Guire
2018-12-18 9:00 ` Miroslav Benes
2018-12-18 8:49 ` Miroslav Benes [this message]
2018-12-18 15:18 ` Joe Lawrence
2019-01-22 16:30 ` Joe Lawrence
2019-01-23 1:10 ` Nicholas Mc Guire
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