From mboxrd@z Thu Jan 1 00:00:00 1970 From: Laszlo Ersek Subject: Re: [Qemu-devel] [PATCH v5 1/4] firmware: introduce sysfs driver for QEMU's fw_cfg device Date: Tue, 24 Nov 2015 18:44:33 +0100 Message-ID: <5654A201.2070902@redhat.com> References: <1448294264-17388-2-git-send-email-somlo@cmu.edu> <201511240404.AFpczj7x%fengguang.wu@intel.com> <20151124165553.GA22627@HEDWIG.INI.CMU.EDU> <5654A08A.6030002@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <5654A08A.6030002-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> Sender: devicetree-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Eric Blake , "Gabriel L. Somlo" , kbuild test robot Cc: mark.rutland-5wv7dgnIgG8@public.gmane.org, peter.maydell-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org, mst-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, stefanha-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, qemu-devel-qX2TKyscuCcdnm+yROfE0A@public.gmane.org, eric-WhKQ6XTQaPysTnJN9+BGXg@public.gmane.org, kraxel-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, pawel.moll-5wv7dgnIgG8@public.gmane.org, zajec5-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, galak-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org, rmk+kernel-lFZ/pmaqli7XmaaqVzeoHQ@public.gmane.org, hanjun.guo-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org, devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, arnd-r2nGTMty4D4@public.gmane.org, ijc+devicetree-KcIKpvwj1kUDXYZnReoRVg@public.gmane.org, jordan.l.justen-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org, agross-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org, leif.lindholm-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org, robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, ard.biesheuvel-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org, gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org, kbuild-all-JC7UmRfGjtg@public.gmane.org, sudeep.holla-5wv7dgnIgG8@public.gmane.org, pbonzini-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, revol-GANU6spQydw@public.gmane.org List-Id: devicetree@vger.kernel.org On 11/24/15 18:38, Eric Blake wrote: > On 11/24/2015 09:55 AM, Gabriel L. Somlo wrote: >> On Tue, Nov 24, 2015 at 04:14:50AM +0800, kbuild test robot wrote: > >>> >>> drivers/firmware/qemu_fw_cfg.c: In function 'fw_cfg_cmdline_set': >>>>> drivers/firmware/qemu_fw_cfg.c:510:7: warning: format '%lli' expects argument of type 'long long int *', but argument 3 has type 'phys_addr_t *' [-Wformat=] >>> &ctrl_off, &data_off, &consumed); >>> ^ >> >> Oh, I think I know why this happened: >> > >> >> So, I could use u64 instead of phys_addr_t and resource_size_t, and >> keep "%lli" (or "%Li"), but then I'd have to check if the parsed value > > %Li is not POSIX. Don't use it (stick with %lli). > >> would overflow a 32-bit address value on arches where phys_addr_t is >> u32, which would make things a bit more messy and awkward. >> >> I'm planning on #ifdef-ing the format string instead: >> >> #ifdef CONFIG_PHYS_ADDR_T_64BIT >> #define PH_ADDR_SCAN_FMT "@%Li%n:%Li:%Li%n" >> #else >> #define PH_ADDR_SCAN_FMT "@%li%n:%li:%li%n" >> #endif > > A more typical approach is akin to ; have PH_ADDR_FMT > defined to either "lli" or "li", then write sscanf(str, "@%"PH_ADDR_FMT > "%n:..., ...), using PH_ADDR_FMT multiple times. > >> ... >> processed = sscanf(str, PH_ADDR_SCAN_FMT, >> &base, &consumed, >> &ctrl_off, &data_off, &consumed); > > Umm, why are you passing &consumed to more than one sscanf() %? That's > (probably) undefined behavior. > > [In general, sscanf() is a horrid interface to use for parsing integers > - it has undefined behavior if the input text would trigger integer > overflow, making it safe to use ONLY on text that you control and can > guarantee won't overflow. By the time you've figured out if untrusted > text meets the requirement for safe parsing via sscanf(), you've > practically already parsed it via safer strtol() and friends.] > Yes, but this is the kernel, which may or may not follow POSIX semantics. (And may or may not curse at POSIX in the process, either way! :)) Laszlo -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html