Hello Alex, On 8/24/20 3:29 PM, Alejandro Colomar wrote: >>From 5df5cae0fb6973df0ab8b3629934f808487112b0 Mon Sep 17 00:00:00 2001 > From: Alejandro Colomar <colomar.6.4.3@xxxxxxxxx> > Date: Fri, 21 Aug 2020 16:58:12 +0200 > Subject: [PATCH] memusage.1, bind.2, eventfd.2, futex.2, > open_by_handle_at.2, > perf_event_open.2, poll.2, signalfd.2, sysctl.2, timerfd_create.2, > bsearch.3, > cmsg.3, getaddrinfo.3, getaddrinfo_a.3 getgrouplist.3, insque.3, > malloc_info.3, mbsinit.3, mbstowcs.3, pthread_create.3, > pthread_setaffinity_np.3, queue.3, rtnetlink.3, shm_open.3, strptime.3, > tsearch.3, aio.7, fanotify.7, inotify.7, unix.7: Use sizeof consistently > > Use ``sizeof`` consistently through all the examples, in the following > way: I would really have preferred three patches here, since: > - Never use a space after ``sizeof``, and always use parentheses > instead. > > Rationale: > > https://www.kernel.org/doc/html/v5.8/process/coding-style.html#spaces (1) This is completely unproblematic from my point of view. > - Use the name of the variable instead of the type as argument > for ``sizeof``, wherever possible. > > Rationale: > > https://www.kernel.org/doc/html/v5.8/process/coding-style.html#allocating-memory (2) This one is up for debate. In many cases it makes sense to do this. However, there are cases where I think that using the struct name can actually help readability. And when I grep through the kernel source, of around 139k lines that use "sizeof", some 37k take a 'struct type' as an argument. SI, I think this kind of change may need to be considered on a case by case basis, rather than as a blanket change. > - When the result of ``sizeof`` is multiplied (or otherwise modified), > write ``sizeof`` in the first place. > > Rationale: > > ``(sizeof(x) * INT_MAX * 2)`` doesn't overflow. > > ``(INT_MAX * 2 * sizeof(x))`` overflows, giving incorrect > results. (3) Is this true? "gcc -Wall" does not complain about this. And, I thought that in both cases, all operands in the expression would be promoted to the largest type. And, on my x86-64 system, sizeof((sizeof(x) * INT_MAX * 2)) == 8 sizeof(INT_MAX * 2 * sizeof(x)) == 8 But, I will say tht I'm not a language lawyer, and C still sometimes has surprises for me. At the least, I'd like to know more about this point. Thanks, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/
