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Tue, 7 Jul 2020 08:38:38 +0000 (UTC) Date: Tue, 7 Jul 2020 09:38:35 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= Subject: Re: [PATCH v2] util/qemu-option: Document the get_opt_value() function Message-ID: <20200707083835.GA2649462@redhat.com> References: <20200629070858.19850-1-philmd@redhat.com> <1dec6cd5-42f8-8e9f-cc87-108e46a926cc@linaro.org> <82bd90f7-9e08-8ada-2a87-b031ea1d116f@amsat.org> MIME-Version: 1.0 In-Reply-To: <82bd90f7-9e08-8ada-2a87-b031ea1d116f@amsat.org> User-Agent: Mutt/1.14.3 (2020-06-14) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=berrange@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Disposition: inline Received-SPF: pass client-ip=207.211.31.120; envelope-from=berrange@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/07 00:46:09 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -40 X-Spam_score: -4.1 X-Spam_bar: ---- X-Spam_report: (-4.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: Damien Hedde , Kevin Wolf , Richard Henderson , qemu-devel@nongnu.org, Markus Armbruster Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, Jul 07, 2020 at 04:14:40AM +0200, Philippe Mathieu-Daudé wrote: > On 7/7/20 3:14 AM, Richard Henderson wrote: > > On 6/29/20 12:08 AM, Philippe Mathieu-Daudé wrote: > >> Coverity noticed commit 950c4e6c94 introduced a dereference before > >> null check in get_opt_value (CID1391003): > >> > >> In get_opt_value: All paths that lead to this null pointer > >> comparison already dereference the pointer earlier (CWE-476) > >> > >> We fixed this in commit 6e3ad3f0e31, but relaxed the check in commit > >> 0c2f6e7ee99 because "No callers of get_opt_value() pass in a NULL > >> for the 'value' parameter". > >> > >> Since this function is publicly exposed, it risks new users to do > >> the same error again. Avoid that documenting the 'value' argument > >> must not be NULL. > > > > I think we should also add some use of __attribute__((nonnull(...))) to enforce > > this within the compiler. > > > > I recently did this without a qemu/compiler.h QEMU_FOO wrapper within > > target/arm. But the nonnull option has optional arguments, so it might be > > difficult to wrap in macros. > > I have this patch after your suggestion from last year: > > +#if __has_attribute(nonnull) > +# define QEMU_NONNULL(LIST) __attribute__((nonnull((LIST)))) > +#else > +# define QEMU_NONNULL(LIST) > +#endif The if/else branch is not required, as both clang and gcc support this, and they are our only supported compilers. Beware that __attribute__((nonnul)) has side-effects, as it was originally implemented as a hint for the optimizer. It allows it to eliminate any code in the method that does a comparison to NULL. Historically it only generated warning messages in very few scenarios involving a literal NULL. Only more recently with -fanalyzer can it generate warnings about indirect passing of NULL via variables. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|