From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas Petazzoni Date: Thu, 17 Mar 2016 21:36:30 +0100 Subject: [Buildroot] [PATCH 02/16] arch/arm: Cortex-M3 provides only Thumb-2 In-Reply-To: <56E9E177.5000606@mind.be> References: <1458164602-16983-1-git-send-email-thomas.petazzoni@free-electrons.com> <1458164602-16983-3-git-send-email-thomas.petazzoni@free-electrons.com> <56E9E177.5000606@mind.be> Message-ID: <20160317213630.54f60dd6@free-electrons.com> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: buildroot@busybox.net Hello, On Wed, 16 Mar 2016 23:43:03 +0100, Arnout Vandecappelle wrote: > On 03/16/16 22:43, Thomas Petazzoni wrote: > > The Cortex-M cores only support Thumb-2, not Thumb. In fact, Thumb-2 > > is a superset of Thumb, > > If thumb2 is a superset of thumb, then CPU_HAS_THUMB2 should select > CPU_HAS_THUMB. And according to [1], it really is a superset. Thinking more about this, I don't see the point. Even if Thumb2 is strictly speaking a superset of Thumb1, there is no gcc flag or mechanism that will allow you to generate Thumb1 code on a Thumb2-capable core. Therefore, it IMO doesn't bring any benefit to select CPU_HAS_THUMB from CPU_HAS_THUMB2. Thomas -- Thomas Petazzoni, CTO, Free Electrons Embedded Linux, Kernel and Android engineering http://free-electrons.com