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Wed, 29 Jan 2020 17:02:37 +0000 (UTC) Received: from oldenburg2.str.redhat.com (dhcp-192-227.str.redhat.com [10.33.192.227]) by smtp.corp.redhat.com (Postfix) with ESMTPS id DFC7587B02; Wed, 29 Jan 2020 17:02:35 +0000 (UTC) From: Florian Weimer To: Segher Boessenkool Subject: Re: powerpc Linux scv support and scv system call ABI proposal References: <1580207907.c96c1lh9t0.astroid@bobo.none> <87tv4fd8wp.fsf@oldenburg2.str.redhat.com> <1580218232.2tezmthp1x.astroid@bobo.none> <20200128154026.GI22482@gate.crashing.org> <87o8unbm8u.fsf@oldenburg2.str.redhat.com> <20200128200133.GJ22482@gate.crashing.org> <87wo9a8cc8.fsf@oldenburg2.str.redhat.com> <20200129162947.GN22482@gate.crashing.org> Date: Wed, 29 Jan 2020 18:02:34 +0100 In-Reply-To: <20200129162947.GN22482@gate.crashing.org> (Segher Boessenkool's message of "Wed, 29 Jan 2020 10:29:47 -0600") Message-ID: <87imku8ac5.fsf@oldenburg2.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-MC-Unique: qlXFv4i6PUuc6DxcfyzdEw-1 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain 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: , Cc: libc-alpha@sourceware.org, Tulio Magno Quites Machado Filho , linuxppc-dev@lists.ozlabs.org, Nicholas Piggin Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" * Segher Boessenkool: > On Wed, Jan 29, 2020 at 05:19:19PM +0100, Florian Weimer wrote: >> * Segher Boessenkool: >> >> But GCC doesn't expose them as integers to C code, so you can't do mu= ch >> >> without them. >> > >> > Sure, it doesn't expose any other registers directly, either. >>=20 >> I can use r0 & 1 with a register variable r0 to check a bit. > > That is not reliable, or supported, and it *will* break. This is > explicit for local register asm, and global register asm is > underdefined. Ugh. I did not know that. And neither did the person who wrote powerpc64/sysdep.h because it uses register variables in regular C expressions. 8-( Other architectures are affected as well. One set of issues is less of a problem if system call arguments are variables and not complex expressions, so that side effects do not clobber registers in the initialization: =09register long __a0 asm ("$4") =3D (long) (arg1); But I wasn't aware of that constraint on the macro users at all. Thanks, Florian