linux-kernel - Re: [PATCH 0/8] unwind, arm64: add sframe unwinder for kernel

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Message-ID: <mb61p1pw21f0v.fsf@kernel.org>
Date: Thu, 13 Feb 2025 07:26:40 +0000
From: Puranjay Mohan <puranjay@...nel.org>
To: Song Liu <song@...nel.org>, Indu Bhagat <indu.bhagat@...cle.com>
Cc: Weinan Liu <wnliu@...gle.com>, Josh Poimboeuf <jpoimboe@...nel.org>,
 Steven Rostedt <rostedt@...dmis.org>, Peter Zijlstra
 <peterz@...radead.org>, Mark Rutland <mark.rutland@....com>,
 roman.gushchin@...ux.dev, Will Deacon <will@...nel.org>, Ian Rogers
 <irogers@...gle.com>, linux-toolchains@...r.kernel.org,
 linux-kernel@...r.kernel.org, live-patching@...r.kernel.org,
 joe.lawrence@...hat.com, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 0/8] unwind, arm64: add sframe unwinder for kernel

Song Liu <song@...nel.org> writes:

> On Wed, Feb 12, 2025 at 4:10 PM Indu Bhagat <indu.bhagat@...cle.com> wrote:
>>
>> On 2/12/25 3:32 PM, Song Liu wrote:
>> > I run some tests with this set and my RFC set [1]. Most of
>> > the test is done with kpatch-build. I tested both Puranjay's
>> > version [3] and my version [4].
>> >
>> > For gcc 14.2.1, I have seen the following issue with this
>> > test [2]. This happens with both upstream and 6.13.2.
>> > The livepatch loaded fine, but the system spilled out the
>> > following warning quickly.
>> >
>>
>> In presence of the issue
>> https://sourceware.org/bugzilla/show_bug.cgi?id=32666, I'd expect bad
>> data in SFrame section.  Which may be causing this symptom?
>>
>> To be clear, the issue affects loaded kernel modules.  I cannot tell for
>> certain - is there module loading involved in your test ?
>
> The KLP is a module, I guess that is also affected?
>
> During kpatch-build, we added some logic to drop the .sframe section.
> I guess this is wrong, as we need the .sframe section when we apply
> the next KLP. However, I don't think the issue is caused by missing
> .sframe section.

Hi, I did the same testing and did not get the Warning.

I am testing on the 6.12.11 kernel with GCC 11.4.1.

Just to verify, the patch we are testing is:

--- >8 ---

diff -Nupr src.orig/kernel/fork.c src/kernel/fork.c
--- src.orig/kernel/fork.c      2023-01-12 11:20:05.408700033 -0500
+++ src/kernel/fork.c   2023-01-12 11:21:19.186137466 -0500
@@ -1700,10 +1700,18 @@ static void posix_cpu_timers_init_group(
        posix_cputimers_group_init(pct, cpu_limit);
 }

+void kpatch_foo(void)
+{
+       if (!jiffies)
+               printk("kpatch copy signal\n");
+}
+
 static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
 {
        struct signal_struct *sig;

+       kpatch_foo();
+
        if (clone_flags & CLONE_THREAD)
                return 0;
--- 8< ---

P.S. - I have a downstream patch for create-diff-object to generate .sframe sections for
livepatch module, will add it to the PR after some cleanups.

Thanks,
Puranjay

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