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Mon, 23 Dec 2019 18:27:54 -0800 (PST) X-Gm-Message-State: APjAAAVBrzegnz259z54h13gSlW9rSgk6FmMpCcBdFk/yOgTnnt8yXbZ xYWCHBHgCcqMrqQqVlg53SdPNUJ1IK4dWwU/ZqhgPg== X-Google-Smtp-Source: APXvYqzX7Wx0WQQGQxSsSx/rylu702E8XhFQtmBzrPd/vN45dmJAZ0EePwEz406rgBkEgebEu04CDi9IHkjEhDWde+I= X-Received: by 2002:adf:f20b:: with SMTP id p11mr31631213wro.195.1577154472974; Mon, 23 Dec 2019 18:27:52 -0800 (PST) MIME-Version: 1.0 References: <02861d0a05c2d48db4e9ee9093e2e2598093c372.1577111366.git.christophe.leroy@c-s.fr> In-Reply-To: <02861d0a05c2d48db4e9ee9093e2e2598093c372.1577111366.git.christophe.leroy@c-s.fr> From: Andy Lutomirski Date: Mon, 23 Dec 2019 18:27:40 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [RFC PATCH v2 04/10] lib: vdso: get pointer to vdso data from the arch To: Christophe Leroy X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20191223_182755_068019_02A0999A X-CRM114-Status: GOOD ( 11.52 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Arnd Bergmann , Benjamin Herrenschmidt , X86 ML , LKML , "open list:MIPS" , Paul Mackerras , Andrew Lutomirski , Michael Ellerman , Thomas Gleixner , Vincenzo Frascino , linuxppc-dev , linux-arm-kernel Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, Dec 23, 2019 at 6:31 AM Christophe Leroy wrote: > > On powerpc, __arch_get_vdso_data() clobbers the link register, > requiring the caller to set a stack frame in order to save it. > > As the parent function already has to set a stack frame and save > the link register to call the C vdso function, retriving the > vdso data pointer there is lighter. I'm confused. Can't you inline __arch_get_vdso_data()? Or is the issue that you can't retrieve the program counter on power without clobbering the link register? I would imagine that this patch generates worse code on any architecture with PC-relative addressing modes (which includes at least x86_64, and I would guess includes most modern architectures). --Andy _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel