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Date:   Tue, 22 Mar 2022 13:15:58 +0000
From:   Mark Rutland <mark.rutland@arm.com>
To:     Masami Hiramatsu <mhiramat@kernel.org>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Stephen Rothwell <sfr@canb.auug.org.au>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux Next Mailing List <linux-next@vger.kernel.org>,
        rostedt@goodmis.org, ast@kernel.org, hjl.tools@gmail.com,
        rick.p.edgecombe@intel.com, rppt@kernel.org,
        linux-toolchains@vger.kernel.org, Andrew.Cooper3@citrix.com,
        ndesaulniers@google.com
Subject: Re: linux-next: build warnings after merge of the tip tree
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On Tue, Mar 22, 2022 at 02:31:36PM +0900, Masami Hiramatsu wrote:
> On Mon, 21 Mar 2022 17:48:54 +0100
> Peter Zijlstra <peterz@infradead.org> wrote:
> 
> > On Mon, Mar 21, 2022 at 02:04:05PM +0100, Peter Zijlstra wrote:
> > > On Mon, Mar 21, 2022 at 01:55:49PM +0100, Peter Zijlstra wrote:
> > > > On Mon, Mar 21, 2022 at 02:03:27PM +1100, Stephen Rothwell wrote:
> > > > > Hi all,
> > > > > 
> > > > > After merging the tip tree, today's linux-next build (x864 allmodconfig)
> > > > > produced these new warnings:
> > > > > 
> > > > > vmlinux.o: warning: objtool: arch_rethook_prepare()+0x55: relocation to !ENDBR: arch_rethook_trampoline+0x0
> > > > > vmlinux.o: warning: objtool: arch_rethook_trampoline_callback()+0x3e: relocation to !ENDBR: arch_rethook_trampoline+0x0
> > > > > vmlinux.o: warning: objtool: unwind_next_frame()+0x93e: relocation to !ENDBR: arch_rethook_trampoline+0x0
> > > > > vmlinux.o: warning: objtool: unwind_next_frame()+0x5f2: relocation to !ENDBR: arch_rethook_trampoline+0x0
> > > > > vmlinux.o: warning: objtool: unwind_next_frame()+0x4a7: relocation to !ENDBR: arch_rethook_trampoline+0x0
> > > > > vmlinux.o: warning: objtool: __rethook_find_ret_addr()+0x81: relocation to !ENDBR: arch_rethook_trampoline+0x0
> > > > > vmlinux.o: warning: objtool: __rethook_find_ret_addr()+0x90: relocation to !ENDBR: arch_rethook_trampoline+0x0
> > > > > vmlinux.o: warning: objtool: rethook_trampoline_handler()+0x8c: relocation to !ENDBR: arch_rethook_trampoline+0x0
> > > > > vmlinux.o: warning: objtool: rethook_trampoline_handler()+0x9b: relocation to !ENDBR: arch_rethook_trampoline+0x0
> > > > 
> > > > Hurmph, lemme go figure out where that code comes from, I've not seen
> > > > those.
> > > 
> > > Ahh, something tracing. I'll go do some patches on top of it.
> > 
> > The below gets rid of the objtool warnings.
> 
> Yes, I confirmed that.
> 
> > But I still think it's fairly terrible to get a (flawed) carbon copy of
> > the kretprobe code.
> 
> Indeed. I would like to replace the trampoline code of kretprobe with
> rethook, eventually. There is no reason why we keep the clone.
> (But I need more arch maintainers help for that, there are too many
>  archs implemented kretprobes)

FWIW, I'm more than happy to help on the arm64 side if you could Cc me for
that; I'm aware of other things in this area I'd like to clean up for
backtracing, too.

Thanks,
Mark.