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Riedl" , Stan Johnson , linuxppc-dev@lists.ozlabs.org, Riccardo Mottola Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" This message is in MIME format. The first part should be readable text, while the remaining parts are likely unreadable without MIME-aware tools. ---1463811774-309288174-1636068978=:9477 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE On Thu, 4 Nov 2021, Christophe Leroy wrote: > Le 02/11/2021 =C3=A0 03:20, Finn Thain a =C3=A9crit=C2=A0: > > Hi Christopher, > >=20 > > After many builds and tests, Stan and I were able to determine that thi= s > > regression only affects builds with CONFIG_USER_NS=3Dy. That is, > >=20 > > d3ccc9781560 + CONFIG_USER_NS=3Dy --> fail > > d3ccc9781560 + CONFIG_USER_NS=3Dn --> okay > > d3ccc9781560~ + CONFIG_USER_NS=3Dy --> okay > > d3ccc9781560~ + CONFIG_USER_NS=3Dn --> okay > >=20 > > Stan also tested a PowerMac G3 system and found that the regression is = not > > present there. Thus far, only PowerMac G4 systems are known to be affec= ted > > (Stan's Cube and Riccardo's PowerBook). > >=20 > > I asked Stan to try v5.15-rc after reverting commit d3ccc9781560. > > Unexpectedly, this build had the same issue. So, it appears there are > > multiple bad commits that produce this Xorg failure, of which d3ccc9781= 560 > > is just the first. > >=20 > > But there's no easy way to identify the other bad commits using bisecti= on. > > So I've addressed this message to you. Can you help fix this regression= ? > >=20 >=20 > I'm wondering if this commit is really the cause of the problem. >=20 > Are you using GCC 11 ? >=20 > If yes, I think it could be a false positive, fixed by > https://github.com/linuxppc/linux/commit/7315e457d6bc >=20 > Can you try with GCC 10 or older ? >=20 AFAIK, all of Stan's builds were made with gcc 10. > Can you cherry pick 7315e457d6bc ("powerpc/uaccess: Fix __get_user() with > CONFIG_CC_HAS_ASM_GOTO_OUTPUT") on top of d3ccc9781560 and see what happe= ns ? >=20 $ git checkout d3ccc9781560 $ git cherry-pick 7315e457d6bc Auto-merging arch/powerpc/include/asm/uaccess.h CONFLICT (content): Merge conflict in arch/powerpc/include/asm/uaccess.h error: could not apply 7315e457d6bc... powerpc/uaccess: Fix __get_user() wi= th CONFIG_CC_HAS_ASM_GOTO_OUTPUT There is no __get_user_asm2_goto in this tree, and __get_user_asm2 already has the "=3D&r" constraint: #define __get_user_asm2(x, addr, err) \ __asm__ __volatile__( \ "1: lwz%X2 %1, %2\n" \ "2: lwz%X2 %L1, %L2\n" \ "3:\n" \ ".section .fixup,\"ax\"\n" \ "4: li %0,%3\n" \ " li %1,0\n" \ " li %1+1,0\n" \ " b 3b\n" \ ".previous\n" \ EX_TABLE(1b, 4b) \ EX_TABLE(2b, 4b) \ : "=3Dr" (err), "=3D&r" (x) \ : "m" (*addr), "i" (-EFAULT), "0" (err))=20 ---1463811774-309288174-1636068978=:9477--