From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jamie Lokier Subject: Re: [PATCH 1/2] arm: Replace CONFIG_HAS_TLS_REG with HWCAP_TLS and check for it on V6 Date: Tue, 22 Jun 2010 18:00:20 +0100 Message-ID: <20100622170020.GF4371@shareable.org> References: <20100621133749.24299.36154.stgit@baageli.muru.com> <20100621135120.24299.98499.stgit@baageli.muru.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mail2.shareable.org ([80.68.89.115]:55260 "EHLO mail2.shareable.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751321Ab0FVRAX (ORCPT ); Tue, 22 Jun 2010 13:00:23 -0400 Content-Disposition: inline In-Reply-To: <20100621135120.24299.98499.stgit@baageli.muru.com> Sender: linux-omap-owner@vger.kernel.org List-Id: linux-omap@vger.kernel.org To: Tony Lindgren Cc: linux-arm-kernel@lists.infradead.org, linux-omap@vger.kernel.org Tony Lindgren wrote: > __kuser_get_tls: @ 0xffff0fe0 > - > -#if !defined(CONFIG_HAS_TLS_REG) && !defined(CONFIG_TLS_REG_EMUL) > - ldr r0, [pc, #(16 - 8)] @ TLS stored at 0xffff0ff0 > -#else > - mrc p15, 0, r0, c13, c0, 3 @ read TLS register > -#endif > + ldr r0, [pc, #(20 - 8)] @ software TLS set in 0xffff0ff4? > + cmp r0, #0 @ hardware TLS if flag not set > + mrceq p15, 0, r0, c13, c0, 3 @ read hardware TLS register > + ldrne r0, [pc, #(12 - 8)] @ software TLS val at 0xffff0ff8 > usr_ret lr > - > - .rep 5 > - .word 0 @ pad up to __kuser_helper_version > - .endr > + .word 0 @ non-zero for software TLS > + .word 0 @ software TLS value It'd be nice not to waste instructions checking for HWCAP_TLS on archs which definitely don't have it. I guess it doesn't matter elsewhere; I'd expect this to be a warm path for some programs making extensive use of TLS (I haven't measured though). As it's only a single instruction, and the code is in a writable page already (copied at init), how about just patching the instruction when ELF_HWCAP is set? -- Jamie