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a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=BwuEtmyXe7F2cR0q4/BzPn1A0ke23BiGgvDQhdo0WMU=; b=qgolYIqXCcbXtGEx7fT0NV1+MlfblfRhEBW70Cz4mLvMBFzaJhZ/EZbeD9txyyiLuA Bg+e+8N7ZrGMiVVwh5JE2HVj9nOprxB6Q+YnDD3pLZnD+F+nNM4QNszACKDVqGiTHUVH P1CBhE0a0k9C5oRqCz1pn4U4hUGP3BuieGS9FPRpeT5LKr79Z/YAdJA77HON/yU457GR F7cWesVVfU/uGgwSiGduE0WOdGnBU7qJRmBWUrf41NVjaIJ8WgSfDgQYyJtOdCMGsur5 JSpIlCJ3tc545M0RROzM/BFjkHJ/6iEhsnaFqVk8zWSWq1NSbCtCwhzor0d/1WgYEumL yVsg== X-Gm-Message-State: AOAM531fTBFYjWZ6gR04mNM60b4mbS7RjkFfSknzlmMQ0x+7WFCqwDZG XO7CdbR/XP1HDq6JKTlHTjrZjJLdQ3dyoxUSl2nc5Q== X-Google-Smtp-Source: ABdhPJzTTihf74kYnNBBzSlXexZpmKM7vZMRAKfIQLzvqwFNAx6uvnwDBIQzEJ98cMtCA2J/JaapvP+XgOC8JK4Jyhw= X-Received: by 2002:a17:906:7492:: with SMTP id e18mr4301672ejl.375.1599171125797; Thu, 03 Sep 2020 15:12:05 -0700 (PDT) MIME-Version: 1.0 References: <20200624203200.78870-1-samitolvanen@google.com> <20200903203053.3411268-1-samitolvanen@google.com> <20200903203053.3411268-9-samitolvanen@google.com> <202009031456.C058EC4@keescook> In-Reply-To: <202009031456.C058EC4@keescook> From: Sami Tolvanen Date: Thu, 3 Sep 2020 15:11:54 -0700 Message-ID: Subject: Re: [PATCH v2 08/28] x86, build: use objtool mcount To: Kees Cook X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200903_181207_447552_200ADF98 X-CRM114-Status: GOOD ( 17.54 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-arch , X86 ML , "Paul E. McKenney" , Kernel Hardening , Peter Zijlstra , Greg Kroah-Hartman , Masahiro Yamada , linux-kbuild , Nick Desaulniers , LKML , Steven Rostedt , clang-built-linux , linux-pci@vger.kernel.org, Will Deacon , linux-arm-kernel Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Sep 3, 2020 at 2:58 PM Kees Cook wrote: > > On Thu, Sep 03, 2020 at 01:30:33PM -0700, Sami Tolvanen wrote: > > Select HAVE_OBJTOOL_MCOUNT if STACK_VALIDATION is selected to use > > objtool to generate __mcount_loc sections for dynamic ftrace with > > Clang and gcc <5. > > > > Signed-off-by: Sami Tolvanen > > Am I right to understand that this fixes mcount for Clang generally > (i.e. it's not _strictly_ related to LTO, though LTO depends on this > change)? No, this works fine with Clang when LTO is disabled, because recordmcount ignores files named "ftrace.o". However, with LTO, we process vmlinux.o instead, so we need a different method of ignoring __fentry__ relocations that are not calls. In v1, I used a function attribute to whitelist functions that refer to __fentry__, but as Peter pointed out back then, objtool already knows where the call sites are, so using it to generate __mcount_loc is cleaner. > And does this mean mcount was working for gcc < 5? Yes. I should have been clearer in the commit message. The reason I mentioned gcc <5 is that later gcc versions support -mrecord-mcount, which means they don't need an external tool for generating __mcount_loc anymore. Sami _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel