From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Joe Lawrence <joe.lawrence@redhat.com>
Cc: Nicholas Mc Guire <der.herr@hofr.at>,
Nicholas Mc Guire <hofrat@osadl.org>,
Jessica Yu <jeyu@kernel.org>, Jiri Kosina <jikos@kernel.org>,
Miroslav Benes <mbenes@suse.cz>, Petr Mladek <pmladek@suse.com>,
live-patching@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2 V2] livepatch: handle kzalloc failure properly
Date: Thu, 13 Dec 2018 14:49:58 -0600 [thread overview]
Message-ID: <20181213204958.tkapx6qi7fnm5t6h@treble> (raw)
In-Reply-To: <7aa8369b-0e64-ecf4-79a1-986c6ffeb59b@redhat.com>
On Thu, Dec 13, 2018 at 03:39:20PM -0500, Joe Lawrence wrote:
> Ahh, I understand the question now. Yeah, by making those routines local
> static, the compiler applied optimizations that renamed the symbols:
>
> noinline static
> % readelf --syms samples/livepatch/livepatch-shadow-mod.o | grep dummy_
> 5: 0000000000000000 20 FUNC LOCAL DEFAULT 1 dummy_check.isra.0
> 7: 0000000000000020 52 FUNC LOCAL DEFAULT 1 dummy_free.constprop.1
> 12: 00000000000000c0 32 OBJECT LOCAL DEFAULT 3 dummy_list_mutex
> 13: 00000000000000e0 16 OBJECT LOCAL DEFAULT 3 dummy_list
> 15: 0000000000000160 115 FUNC LOCAL DEFAULT 1 dummy_alloc
>
>
> I can avoid that optimization (and successfully load all the modules)
> by using either:
>
> __attribute__((optimize("O0"))) noinline static
> % readelf --syms samples/livepatch/livepatch-shadow-mod.o | grep dummy_
> 6: 0000000000000000 6016 FUNC LOCAL DEFAULT 1 dummy_alloc
> 11: 00000000000000c0 32 OBJECT LOCAL DEFAULT 3 dummy_list_mutex
> 12: 00000000000000e0 16 OBJECT LOCAL DEFAULT 3 dummy_list
> 14: 0000000000001810 73 FUNC LOCAL DEFAULT 1 dummy_free
> 16: 0000000000001860 108 FUNC LOCAL DEFAULT 1 dummy_check
>
> or:
>
> __noclone noinline static
> % readelf --syms samples/livepatch/livepatch-shadow-mod.o | grep dummy_
> 5: 0000000000000000 22 FUNC LOCAL DEFAULT 1 dummy_check
> 7: 0000000000000020 51 FUNC LOCAL DEFAULT 1 dummy_free
> 12: 00000000000000c0 32 OBJECT LOCAL DEFAULT 3 dummy_list_mutex
> 13: 00000000000000e0 16 OBJECT LOCAL DEFAULT 3 dummy_list
> 15: 0000000000000160 115 FUNC LOCAL DEFAULT 1 dummy_alloc
>
> but I'm not sure if either is the definitive way to avoid such
> optimization. Anyone know for sure?
Yeah, for now I think "static __noclone" is the way to go. Soon we'll
have a GCC flag which disables such optimizations for all functions.
And the dummy_list* variables can just be "static".
--
Josh
prev parent reply other threads:[~2018-12-13 20:50 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-13 14:05 [PATCH 1/2 " Nicholas Mc Guire
2018-12-13 14:05 ` [PATCH 2/2 " Nicholas Mc Guire
2018-12-13 14:14 ` Joe Lawrence
2018-12-13 15:39 ` Nicholas Mc Guire
2018-12-13 16:39 ` Joe Lawrence
2018-12-13 18:51 ` Nicholas Mc Guire
2018-12-13 20:39 ` Joe Lawrence
2018-12-13 20:49 ` Josh Poimboeuf [this message]
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