From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yu-cheng Yu Subject: Re: [PATCH v7 22/27] binfmt_elf: Extract .note.gnu.property from an ELF file Date: Tue, 18 Jun 2019 07:58:37 -0700 Message-ID: References: <87lfy9cq04.fsf@oldenburg2.str.redhat.com> <20190611114109.GN28398@e103592.cambridge.arm.com> <031bc55d8dcdcf4f031e6ff27c33fd52c61d33a5.camel@intel.com> <20190612093238.GQ28398@e103592.cambridge.arm.com> <87imt4jwpt.fsf@oldenburg2.str.redhat.com> <20190618091248.GB2790@e103592.cambridge.arm.com> <20190618124122.GH3419@hirez.programming.kicks-ass.net> <87ef3r9i2j.fsf@oldenburg2.str.redhat.com> <20190618125512.GJ3419@hirez.programming.kicks-ass.net> <20190618133223.GD2790@e103592.cambridge.arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20190618133223.GD2790@e103592.cambridge.arm.com> Sender: linux-kernel-owner@vger.kernel.org To: Dave Martin , Peter Zijlstra Cc: Florian Weimer , Thomas Gleixner , x86@kernel.org, "H. Peter Anvin" , Ingo Molnar , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-api@vger.kernel.org, Arnd Bergmann , Andy Lutomirski , Balbir Singh , Borislav Petkov , Cyrill Gorcunov , Dave Hansen , Eugene Syromiatnikov , "H.J. Lu" , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Nadav Amit , Ole List-Id: linux-api@vger.kernel.org On Tue, 2019-06-18 at 14:32 +0100, Dave Martin wrote: > On Tue, Jun 18, 2019 at 02:55:12PM +0200, Peter Zijlstra wrote: > > On Tue, Jun 18, 2019 at 02:47:00PM +0200, Florian Weimer wrote: > > > * Peter Zijlstra: > > > > > > > I'm not sure I read Thomas' comment like that. In my reading keeping the > > > > PT_NOTE fallback is exactly one of those 'fly workarounds'. By not > > > > supporting PT_NOTE only the 'fine' people already shit^Hpping this out > > > > of tree are affected, and we don't have to care about them at all. > > > > > > Just to be clear here: There was an ABI document that required PT_NOTE > > > parsing. > > > > URGH. > > > > > The Linux kernel does *not* define the x86-64 ABI, it only > > > implements it. The authoritative source should be the ABI document. > > > > > > In this particularly case, so far anyone implementing this ABI extension > > > tried to provide value by changing it, sometimes successfully. Which > > > makes me wonder why we even bother to mainatain ABI documentation. The > > > kernel is just very late to the party. > > > > How can the kernel be late to the party if all of this is spinning > > wheels without kernel support? > > PT_GNU_PROPERTY is mentioned and allocated a p_type value in hjl's > spec [1], but otherwise seems underspecified. > > In particular, it's not clear whether a PT_GNU_PROPERTY phdr _must_ be > emitted for NT_GNU_PROPERTY_TYPE_0. While it seems a no-brainer to emit > it, RHEL's linker already doesn't IIUC, and there are binaries in the > wild. > > Maybe this phdr type is a late addition -- I haven't attempted to dig > through the history. > > > For arm64 we don't have this out-of-tree legacy to support, so we can > avoid exhausitvely searching for the note: no PT_GNU_PROPERTY -> > no note. > > So, can we do the same for x86, forcing RHEL to carry some code out of > tree to support their legacy binaries? Or do we accept that there is > already a de facto ABI and try to be compatible with it? > > > From my side, I want to avoid duplication between x86 and arm64, and > keep unneeded complexity out of the ELF loader where possible. Hi Florian, The kernel looks at only ld-linux. Other applications are loaded by ld-linux. So the issues are limited to three versions of ld-linux's. Can we somehow update those?? Thanks, Yu-cheng