From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Evgenii Shatokhin <eshatokhin@virtuozzo.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Kristen Carlson Accardi <kristen@linux.intel.com>,
live-patching@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
linux-kernel@vger.kernel.org,
Konstantin Khorenko <khorenko@virtuozzo.com>
Subject: Re: 'perf probe' and symbols from .text.<something>
Date: Thu, 18 Feb 2021 13:35:08 -0600 [thread overview]
Message-ID: <20210218193508.mw6ugmh6bjlplbwe@treble> (raw)
In-Reply-To: <09257fb8-3ded-07b0-b3cc-55d5431698d8@virtuozzo.com>
On Thu, Feb 18, 2021 at 08:09:17PM +0300, Evgenii Shatokhin wrote:
> Is there a way to allow probing of functions in .text.<something> ?
>
> Of course, one could place probes using absolute addresses of the functions
> but that would be less convenient.
>
> This also affects many livepatch modules where the kernel code can be
> compiled with -ffunction-sections and each function may end up in a separate
> section .text.<function_name>. 'perf probe' cannot be used there, except
> with the absolute addresses.
>
> Moreover, if FGKASLR patches are merged (https://lwn.net/Articles/832434/)
> and the kernel is built with FGKASLR enabled, -ffunction-sections will be
> used too. 'perf probe' will be unable to see the kernel functions then.
A hack fix like the below would probably work, but as you pointed out,
FGKASLR is going to be a problem. I suspect the proper fix is for perf
to learn how to deal with multiple executable ELF sections.
diff --git a/scripts/module.lds.S b/scripts/module.lds.S
index 69b9b71a6a47..0c522a87f6ce 100644
--- a/scripts/module.lds.S
+++ b/scripts/module.lds.S
@@ -4,6 +4,10 @@
* combine them automatically.
*/
SECTIONS {
+ .text : {
+ *(.text)
+ *(.text.*)
+ }
/DISCARD/ : {
*(.discard)
*(.discard.*)
next prev parent reply other threads:[~2021-02-18 19:51 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-18 17:09 'perf probe' and symbols from .text.<something> Evgenii Shatokhin
2021-02-18 19:35 ` Josh Poimboeuf [this message]
2021-02-22 15:05 ` Masami Hiramatsu
2021-02-22 15:12 ` Masami Hiramatsu
2021-02-22 17:51 ` Josh Poimboeuf
2021-02-23 1:23 ` Masami Hiramatsu
2021-02-23 7:36 ` Masami Hiramatsu
2021-02-23 19:45 ` Josh Poimboeuf
2021-02-24 8:00 ` Masami Hiramatsu
2021-02-23 1:48 ` [PATCH] perf-probe: Failback to symbol-base probe for probes on module Masami Hiramatsu
2021-02-23 7:36 ` Masami Hiramatsu
2021-02-23 7:09 ` 'perf probe' and symbols from .text.<something> Masami Hiramatsu
2021-02-23 7:37 ` [PATCH] perf-probe: dso: Add symbols in .text.* subsections to text symbol map in kenrel modules Masami Hiramatsu
2021-02-23 15:02 ` Evgenii Shatokhin
2021-02-23 20:11 ` Arnaldo Carvalho de Melo
2021-02-24 7:47 ` Evgenii Shatokhin
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