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Howlett" , Uros Bizjak , Thomas =?utf-8?Q?Wei=C3=9Fschuh?= , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, kernel-dev@igalia.com Subject: Re: [PATCH RFC 1/2] arm64: vdso: Prepare for robust futex unlock support In-Reply-To: <32642d18-8c83-47ad-8456-1813084c4622@igalia.com> (=?utf-8?Q?=22Andr=C3=A9?= Almeida"'s message of "Wed, 22 Apr 2026 09:46:53 -0300") References: <20260417-tonyk-robust_arm-v1-0-03aa64e2ff1a@igalia.com> <20260417-tonyk-robust_arm-v1-1-03aa64e2ff1a@igalia.com> <32642d18-8c83-47ad-8456-1813084c4622@igalia.com> Date: Wed, 22 Apr 2026 14:56:09 +0200 Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Precedence: bulk X-Mailing-List: linux-arch@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 * Andr=C3=A9 Almeida: > Hi Florian, > > Em 17/04/2026 12:08, Florian Weimer escreveu: >> * Andr=C3=A9 Almeida: >>=20 >>> There will be a VDSO function to unlock non-contended robust futexes in >>> user space. The unlock sequence is racy vs. clearing the list_pending_op >>> pointer in the task's robust list head. To plug this race the kernel ne= eds >>> to know the critical section window so it can clear the pointer when the >>> task is interrupted within that race window. The window is determined by >>> labels in the inline assembly. >>> >>> Signed-off-by: Andr=C3=A9 Almeida >>> --- >>> RFC: Those symbols can't be found by the linker after patch 2/2, it fai= ls with: >>> >>> ld: arch/arm64/kernel/vdso.o: in function `vdso_futex_robust_unlock_upd= ate_ips': >>> arch/arm64/kernel/vdso.c:72:(.text+0x200): undefined reference to `__fu= tex_list64_try_unlock_cs_success' >>> ld: arch/arm64/kernel/vdso.o: relocation R_AARCH64_ADR_PREL_PG_HI21 aga= inst symbol `__futex_list64_try_unlock_cs_success' which may bind externall= y can not be used when making a shared object; recompile with -fPIC >>> arch/arm64/kernel/vdso.c:72:(.text+0x200): dangerous relocation: unsupp= orted relocation >> I think your GLOBLS definition adds a 64 suffix. That shouldn't be >> necessary on AArch64. It's not reflected in the references, so you end >> up with an undefined symbol error. >>=20 > > Why aarch64 doesn't need the 64 suffix? objdump shows that the final > label name is __futex_list64_try_unlock_cs_success, which should match > what the linker is trying to find, AFAIC. Sorry, I was confused about how this is expected to work. Florian