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[60.241.27.127]) by smtp.gmail.com with ESMTPSA id bb18sm5276575pjb.44.2021.05.19.19.46.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 19 May 2021 19:46:02 -0700 (PDT) Date: Thu, 20 May 2021 12:45:57 +1000 From: Nicholas Piggin Subject: Re: Linux powerpc new system call instruction and ABI To: Rich Felker , "Dmitry V. Levin" Cc: Joakim Tjernlund , linux-api@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, Michael Ellerman , musl@lists.openwall.com, Segher Boessenkool References: <20210518231331.GA8464@altlinux.org> <9b5ea7059c5a5d4e9ccccd7d73ce2c66b2203f52.camel@infinera.com> <1621410291.c7si38sa9q.astroid@bobo.none> <1621413143.oec64jaci5.astroid@bobo.none> <20210519143836.GJ10366@gate.crashing.org> <11d62aa2488e51ec00fe77f24a1d7cdcc21af0b8.camel@infinera.com> <20210519152205.GL10366@gate.crashing.org> <20210519234846.GS2546@brightrain.aerifal.cx> <20210520010612.GA25599@altlinux.org> In-Reply-To: <20210520010612.GA25599@altlinux.org> MIME-Version: 1.0 Message-Id: <1621478448.743zqcrxza.astroid@bobo.none> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org Excerpts from Dmitry V. Levin's message of May 20, 2021 11:06 am: > On Wed, May 19, 2021 at 07:48:47PM -0400, Rich Felker wrote: >> On Wed, May 19, 2021 at 06:09:25PM +0000, Joakim Tjernlund wrote: > [...] >> > W.r.t breaking ABI, isn't that what PowerPC is trying to do with the n= ew syscall I/F?=20 >>=20 >> No, it's a new independent interface. >=20 > Unfortunately, being a new independent interface doesn't mean it isn't > an ABI break. In fact, it was a severe ABI break, and this thread is > an attempt to find a hotfix. It is an ABI break, that was known. The ptrace info stuff I fixed with=20 the patch earlier was obviously a bug in my initial implementation and=20 not intended (sorry my ptrace testing was not sufficient, and thanks for reporting it, by the way). But the register ABI was always a known break. The issue is that rfscv clobbers LR, so it can not support the old ABI. If the old ABI did not=20 preserve LR, then we may have chosen to not change register ABI at all. Thanks, Nick