From mboxrd@z Thu Jan 1 00:00:00 1970 From: Frank Rowand Subject: Re: [RFC/PATCH] of: Mark property::value as const Date: Sat, 11 Mar 2017 22:27:08 -0800 Message-ID: <58C4EA3C.4070503@gmail.com> References: <20170214025040.23955-1-stephen.boyd@linaro.org> <58AF6B88.6020709@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <58AF6B88.6020709-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> Sender: devicetree-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Stephen Boyd , Rob Herring Cc: linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: devicetree@vger.kernel.org Hi Stephen, On 02/23/17 15:08, Frank Rowand wrote: > On 02/13/17 18:50, Stephen Boyd wrote: >> The 'blob' we pass into populate_properties() is marked as const, >> but we cast that const away when we assign the result of >> fdt_getprop_by_offset() to pp->value. Let's mark value as const >> instead, so that code can't mistakenly write to the value of the >> property that we've so far advertised as const. > > Instead of struct property field value being a pointer into the > FDT, I would rather copy the data to newly allocated memory and > have value be a pointer to that memory. This is required if we > want to make /sys/firmware/fdt optional, which would allow us to > free the memory containing the initial boot FDT. > > I also do not want overlay live subtrees to have any pointers > into the FDT that was used to populate the overlay, so copying > the data solves that problem also. > > >> Unfortunately, this exposes a problem with the fdt resolver code, >> where we overwrite the value member of properties of phandles to >> update them with their final value. Add a comment for now to >> indicate where we're potentially writing over const data. > > Yes, the resolver code needs to adjust phandle values. > > I think I can get rid of the resolver modifying the various phandle > values, and instead just modify the phandle value in struct > device_node. At the same time, I think I can also remove all > instances of the phandle properties ('linux,phandle', 'ibm,phandle', > 'phandle') in the live tree. These properties should not be > accessed directly by any code outside of the device tree framework > since the phandle is located in the struct device_node. A quick > grep does not show any such accesses of the phandle properties, > but I want to look more closely. After reading through a bit of code, I am confident that I can modify the resolver code to not modify the various phandle property values. There are a few tentacles reaching out to other areas that I will have to fix also. The biggest task for me will be to create some good test code. I'll be unavailable this week, so I'll start on it in about a week. -Frank -- 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