From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Wed, 28 Mar 2018 21:22:42 +0200 From: Greg Kroah-Hartman To: Matthias Kaehlcke Cc: Manoj Gupta , linux-kernel@vger.kernel.org, Josh Poimboeuf , Alexander Potapenko Subject: Re: [PATCH] debugfs: Check return value of debugfs_real_fops() for NULL Message-ID: <20180328192242.GA1404@kroah.com> References: <20180327235553.210165-1-mka@chromium.org> <20180328061616.GA8212@kroah.com> <20180328180556.GB32098@kroah.com> <20180328181456.GA87376@google.com> <20180328181936.GA3522@kroah.com> <20180328185009.GB87376@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180328185009.GB87376@google.com> User-Agent: Mutt/1.9.4 (2018-02-28) X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On Wed, Mar 28, 2018 at 11:50:09AM -0700, Matthias Kaehlcke wrote: > El Wed, Mar 28, 2018 at 08:19:36PM +0200 Greg Kroah-Hartman ha dit: > > > On Wed, Mar 28, 2018 at 11:14:56AM -0700, Matthias Kaehlcke wrote: > > > El Wed, Mar 28, 2018 at 08:05:56PM +0200 Greg Kroah-Hartman ha dit: > > > > > > > > > > > A: Because it messes up the order in which people normally read text. > > > > Q: Why is top-posting such a bad thing? > > > > A: Top-posting. > > > > Q: What is the most annoying thing in e-mail? > > > > > > > > A: No. > > > > Q: Should I include quotations after my reply? > > > > > > > > http://daringfireball.net/2007/07/on_top > > > > > > > > On Wed, Mar 28, 2018 at 07:47:53AM -0700, Manoj Gupta wrote: > > > > > Please note that there is nothing wrong in the generated code, just > > > > > that it confuses objtool. > > > > > > > > Then fix the tool, the C code is correct :) > > > > > > > > > Clang has simply omitted the statement where NULL is returned since > > > > > the pointer was always dereferenced post inlining. > > > > > > > > Then tell clang not to do that, like we tell gcc not to do that as that > > > > is a foolish thing for a compiler to do when building the kernel. > > > > > > Thanks all for your input, we'll try to get > > > -fno-delete-null-pointer-checks or a similar flag to be added to > > > clang. > > > > Wait, clang does not have that? > > Nope, clang doesn't currently have such a flag. > > > That's crazy, how has this not been hit yet when building the > > kernel? > > IIRC this patch was needed to work around the lack of the flag: > > commit beaec533fc2701a28a4d667f67c9f59c6e4e0d13 > Author: Alexander Potapenko > Date: Wed Jul 19 20:27:30 2017 +0200 > > llist: clang: introduce member_address_is_nonnull() > > Currently llist_for_each_entry() and llist_for_each_entry_safe() iterate > until &pos->member != NULL. But when building the kernel with Clang, > the compiler assumes &pos->member cannot be NULL if the member's offset > is greater than 0 (which would be equivalent to the object being > non-contiguous in memory). Therefore the loop condition is always true, > and the loops become infinite. > > To work around this, introduce the member_address_is_nonnull() macro, > which casts object pointer to uintptr_t, thus letting the member pointer > to be NULL. > > Signed-off-by: Alexander Potapenko > Tested-by: Sodagudi Prasad > Signed-off-by: Linus Torvalds > > > Other than that I am not aware of any known issues. I think you have gotten lucky :) greg k-h