From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ua0-f199.google.com (mail-ua0-f199.google.com [209.85.217.199]) by kanga.kvack.org (Postfix) with ESMTP id 28BBA6B0038 for ; Mon, 25 Sep 2017 03:37:38 -0400 (EDT) Received: by mail-ua0-f199.google.com with SMTP id c27so6269935uah.1 for ; Mon, 25 Sep 2017 00:37:38 -0700 (PDT) Received: from gate.crashing.org (gate.crashing.org. [63.228.1.57]) by mx.google.com with ESMTPS id s78si1966928vkf.330.2017.09.25.00.37.36 for (version=TLS1 cipher=AES128-SHA bits=128/128); Mon, 25 Sep 2017 00:37:36 -0700 (PDT) Date: Mon, 25 Sep 2017 02:37:21 -0500 From: Segher Boessenkool Subject: Re: [PATCH] mm: fix RODATA_TEST failure "rodata_test: test data was not read only" Message-ID: <20170925073721.GM8421@gate.crashing.org> References: <20170921093729.1080368AC1@po15668-vm-win7.idsi0.si.c-s.fr> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Kees Cook Cc: Christophe Leroy , Michael Ellerman , Jinbum Park , Andrew Morton , "linuxppc-dev@lists.ozlabs.org" , LKML , Linux-MM On Sun, Sep 24, 2017 at 12:17:51PM -0700, Kees Cook wrote: > On Thu, Sep 21, 2017 at 2:37 AM, Christophe Leroy > wrote: > > On powerpc, RODATA_TEST fails with message the following messages: > > > > [ 6.199505] Freeing unused kernel memory: 528K > > [ 6.203935] rodata_test: test data was not read only > > > > This is because GCC allocates it to .data section: > > > > c0695034 g O .data 00000004 rodata_test_data > > Uuuh... that seems like a compiler bug. It's marked "const" -- it > should never end up in .data. I would argue that this has done exactly > what it was supposed to do, and shows that something has gone wrong. > It should always be const. Adding "static" should just change > visibility. (I'm not opposed to the static change, but it seems to > paper over a problem with the compiler...) The compiler puts this item in .sdata, for 32-bit. There is no .srodata, so if it wants to use a small data section, it must use .sdata . Non-external, non-referenced symbols are not put in .sdata, that is the difference you see with the "static". I don't think there is a bug here. If you think there is, please open a GCC bug. Segher -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org