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Howlett" Subject: Re: [patch 8/8] x86/vdso: Implement __vdso_futex_robust_try_unlock() In-Reply-To: <20260319081750-6676c5a6-80c4-4904-a53d-e272a5cfaeb1@linutronix.de> ("Thomas =?utf-8?Q?Wei=C3=9Fschuh=22's?= message of "Thu, 19 Mar 2026 08:41:47 +0100") References: <20260316162316.356674433@kernel.org> <20260316164951.484640267@kernel.org> <20260317081606-6b19f6a3-34e5-4056-9b8b-e9b90028b960@linutronix.de> <87bjgmokb0.ffs@tglx> <20260317120032-5d3d8bb8-27af-4380-9f82-5a132d84a0af@linutronix.de> <87ikatm7rx.ffs@tglx> <20260319081750-6676c5a6-80c4-4904-a53d-e272a5cfaeb1@linutronix.de> Date: Thu, 19 Mar 2026 09:53:53 +0100 Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Precedence: bulk X-Mailing-List: linux-kernel@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 3.4.1 on 10.30.177.4 * Thomas Wei=C3=9Fschuh: > On Wed, Mar 18, 2026 at 05:17:38PM +0100, Thomas Gleixner wrote: >> On Tue, Mar 17 2026 at 12:17, Thomas Wei=C3=9Fschuh wrote: >> >> Due to my pretty limited userspace DSO knowledge that was the best I >> >> came up with. If you have a better idea, please let me know. >> > >> > I would have expected GDB to be able to use the separate vDSO debugging >> > symbols to find these symbols. So far I was not able to make it work, >> > but I blame my limited GDB knowledge. >>=20 >> I got it "working" by manually loading vdso64.so.dbg at the right >> offset, which only took about 10 attempts to get it right. Then you can >> use actual local symbols. >>=20 >> vdso2c picks them up correctly too. > > What also works is to have GDB look up the debug symbols through their > debug ids. At this point the load address of the vDSO is already known. > > $ make vdso_install INSTALL_MOD_PATH=3D$SOME_DIRECTORY > $ gdb -ex "set debug-file-directory $SOME_DIRECTORY/lib/modules/$(uname -= r)/vdso" $BINARY > > Depending on the distribution the vDSO from the kernel package might alre= ady > be set up to be found automatically. > > Maybe we could add a helper to scripts/gdb/ which uses $(vdso-install-y) > to either populate a debug-file-directory automatically or hook into the = GDB > lookup process to avoid these manual steps. If the the /lib/modules/$(uname -r)/vdso/vdsoNN.so path is standard, we can use it in the link map, at the expense of an additional system call during process startup. It isn't just a performance cost. We've seen seccomp filters that kill the process on uname calls. Thanks, Florian