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Fri, 1 Nov 2024 10:15:13 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id ler6DzGqJGe4SAAAD6G6ig (envelope-from ); Fri, 01 Nov 2024 10:15:13 +0000 Received: by quack3.suse.cz (Postfix, from userid 1000) id C6B43A0AF4; Fri, 1 Nov 2024 11:15:12 +0100 (CET) Date: Fri, 1 Nov 2024 11:15:12 +0100 From: Jan Kara To: "Gustavo A. R. Silva" Cc: Jan Kara , "Gustavo A. R. Silva" , Theodore Ts'o , Jan Kara , linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org Subject: Re: [PATCH][next] jbd2: Avoid dozens of -Wflex-array-member-not-at-end warnings Message-ID: <20241101101512.eee2nkaqgffsoxe3@quack3> References: <20241031123313.dfcuttwzzs5f5i7a@quack3> <20241031213208.gzr5jv2kg5eobjuo@quack3> Precedence: bulk X-Mailing-List: linux-ext4@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 586A81FE97 X-Spam-Score: -4.01 X-Rspamd-Action: no action X-Spamd-Result: default: False [-4.01 / 50.00]; BAYES_HAM(-3.00)[99.99%]; NEURAL_HAM_LONG(-1.00)[-1.000]; MID_RHS_NOT_FQDN(0.50)[]; R_DKIM_ALLOW(-0.20)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; ARC_NA(0.00)[]; ASN(0.00)[asn:25478, ipnet:::/0, country:RU]; MISSING_XM_UA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; TO_DN_SOME(0.00)[]; MIME_TRACE(0.00)[0:+]; FUZZY_BLOCKED(0.00)[rspamd.com]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.com:email]; RCVD_COUNT_THREE(0.00)[3]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; RCPT_COUNT_SEVEN(0.00)[8]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; RCVD_TLS_LAST(0.00)[]; DKIM_TRACE(0.00)[suse.cz:+] X-Rspamd-Server: rspamd1.dmz-prg2.suse.org X-Spam-Flag: NO X-Spam-Level: On Thu 31-10-24 17:31:34, Gustavo A. R. Silva wrote: > On 31/10/24 15:32, Jan Kara wrote: > > > > > `sizeof(ctx) == 4` when `char ctx[JBD_MAX_CHECKSUM_SIZE];` > > > > > > To maintain the same size, we tell `DEFINE_RAW_FLEX()` to allocate `1` > > > element for the flex array, as in 32-bit `sizeof(void *) == 4`. > > > > So I agree we end up allocating enough space on stack but it is pretty > > subtle and if JBD_MAX_CHECKSUM_SIZE definition changes, we have a problem. > > I think we need something like (JBD_MAX_CHECKSUM_SIZE + sizeof(*desc->__ctx) > > - 1) / sizeof(*desc->__ctx))? > > I see. Well, in that case it'd be something more like: > > - struct { > - struct shash_desc shash; > - char ctx[JBD_MAX_CHECKSUM_SIZE]; > - } desc; > + DEFINE_RAW_FLEX(struct shash_desc, desc, __ctx, > + (JBD_MAX_CHECKSUM_SIZE + > + sizeof(*((struct shash_desc *)0)->__ctx)) / > + sizeof(*((struct shash_desc *)0)->__ctx)); > > Notice that `desc` is created inside `DEFINE_RAW_FLEX()` Right. Thanks for fixing this. The cleanest option then probably is: DEFINE_RAW_FLEX(struct shash_desc, desc, __ctx, DIV_ROUND_UP(JBD_MAX_CHECKSUM_SIZE, sizeof(*((struct shash_desc *)0)->__ctx))) Honza -- Jan Kara SUSE Labs, CR