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Sullivan" To: Michael Ellerman Cc: Joe Lawrence , live-patching@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, pmladek@suse.com, mbenes@suse.cz, jikos@kernel.org, jpoimboe@kernel.org, naveen.n.rao@linux.ibm.com, christophe.leroy@csgroup.eu, npiggin@gmail.com Subject: Re: [PATCH] powerpc/ftrace: restore r2 to caller's stack on livepatch sibling call Message-ID: References: <87ed6q13xk.fsf@mail.lhotse> <20240815160712.4689-1-rysulliv@redhat.com> <9ec85e72-85dd-e9bc-6531-996413014629@redhat.com> <87bk0wrn1m.fsf@mail.lhotse> Precedence: bulk X-Mailing-List: live-patching@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87bk0wrn1m.fsf@mail.lhotse> X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 On Tue, Sep 10, 2024 at 05:21:57PM +1000, Michael Ellerman wrote: > "Ryan B. Sullivan" writes: > > Hello all, > > > > Just wanted to ping and see if there was any further feedback or > > questions regarding the patch? > Hi Michael, Thank you for the update. > Hi Ryan, > > I'd really like a selftest that triggers the sibling call behaviour. > > As I said upthread I tried writing one but failed. Which you later > explained is because the cross-module sibling call is not generated by > the compiler but rather by the code being objcopy'ed (or similar). > > I think it should be possible to trick the compiler into letting us do a > cross-module sibling call by doing it in an inline asm block. Obviously > that's non-standard, but I think it might work well enough for a test? > > We have an example of calling a function within an inline asm block in > call_do_irq(). If you think that that would be a welcome addition to the patch I can look into adding it, especially if you are busy at the moment. > > I'll try to find time to get that done, but I can't promise when. > > cheers > Cheers, Ryan