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[193.116.108.230]) by smtp.gmail.com with ESMTPSA id iq19sm9351498pjb.48.2020.06.14.02.24.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 14 Jun 2020 02:24:25 -0700 (PDT) Date: Sun, 14 Jun 2020 19:24:18 +1000 From: Nicholas Piggin Subject: Re: [PATCH] powerpc/64: indirect function call use bctrl rather than blrl in ret_from_kernel_thread To: Christophe Leroy , linuxppc-dev@lists.ozlabs.org References: <20200611121119.1015740-1-npiggin@gmail.com> <1c6161a5-fa2f-9e19-a7f3-432bbfe3523b@csgroup.eu> In-Reply-To: <1c6161a5-fa2f-9e19-a7f3-432bbfe3523b@csgroup.eu> MIME-Version: 1.0 Message-Id: <1592124658.jvrxm8juwi.astroid@bobo.none> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Excerpts from Christophe Leroy's message of June 11, 2020 10:26 pm: >=20 >=20 > Le 11/06/2020 =C3=A0 14:11, Nicholas Piggin a =C3=A9crit=C2=A0: >> blrl is not recommended to use as an indirect function call, as it may >> corrupt the link stack predictor. >>=20 >> This is not a performance critical path but this should be fixed for >> consistency. >=20 > There's exactly the same in entry_32.S > Should it be changed there too ... for consistency :) ? >=20 > ppc32 also uses blrl for calling syscall handler, should it be changed=20 > as well ? Yes I would say so. I don't know much about 32-bit implementations but MPC7450 at least has a link stack predictor. Thanks, Nick