From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm1-f66.google.com (mail-wm1-f66.google.com [209.85.128.66]) by mail19.linbit.com (LINBIT Mail Daemon) with ESMTP id 7C3FE4203EB for ; Sat, 13 Jun 2020 11:56:25 +0200 (CEST) Received: by mail-wm1-f66.google.com with SMTP id y20so10152508wmi.2 for ; Sat, 13 Jun 2020 02:56:25 -0700 (PDT) Received: from soda.linbit (62-99-137-214.static.upcbusiness.at. [62.99.137.214]) by smtp.gmail.com with ESMTPSA id 67sm14725945wrk.49.2020.06.13.02.56.24 for (version=TLS1_2 cipher=ECDHE-ECDSA-CHACHA20-POLY1305 bits=256/256); Sat, 13 Jun 2020 02:56:24 -0700 (PDT) Resent-Message-ID: <20200613095622.GF4222@soda.linbit> Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by mail19.linbit.com (LINBIT Mail Daemon) with ESMTP id C8A294203E8 for ; Thu, 7 May 2020 20:53:33 +0200 (CEST) From: "Gustavo A. R. Silva" To: Philipp Reisner , Lars Ellenberg Message-ID: <20200507185212.GA14165@embeddedor> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Cc: linux-kernel@vger.kernel.org, drbd-dev@lists.linbit.com Subject: [Drbd-dev] [PATCH] drbd: Replace zero-length array with flexible-array List-Id: "*Coordination* of development, patches, contributions -- *Questions* \(even to developers\) go to drbd-user, please." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Date: Sat, 13 Jun 2020 09:57:45 -0000 The current codebase makes use of the zero-length array language extension to the C90 standard, but the preferred mechanism to declare variable-length types such as these ones is a flexible array member[1][2], introduced in C99: struct foo { int stuff; struct boo array[]; }; By making use of the mechanism above, we will get a compiler warning in case the flexible array does not occur last in the structure, which will help us prevent some kind of undefined behavior bugs from being inadvertently introduced[3] to the codebase from now on. Also, notice that, dynamic memory allocations won't be affected by this change: "Flexible array members have incomplete type, and so the sizeof operator may not be applied. As a quirk of the original implementation of zero-length arrays, sizeof evaluates to zero."[1] sizeof(flexible-array-member) triggers a warning because flexible array members have incomplete type[1]. There are some instances of code in which the sizeof operator is being incorrectly/erroneously applied to zero-length arrays and the result is zero. Such instances may be hiding some bugs. So, this work (flexible-array member conversions) will also help to get completely rid of those sorts of issues. This issue was found with the help of Coccinelle. [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html [2] https://github.com/KSPP/linux/issues/21 [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") Signed-off-by: Gustavo A. R. Silva --- drivers/block/drbd/drbd_int.h | 2 +- drivers/block/drbd/drbd_protocol.h | 8 ++++---- 2 files changed, 5 insertions(+), 5 deletions(-) diff --git a/drivers/block/drbd/drbd_int.h b/drivers/block/drbd/drbd_int.h index aae99a2d7bd4..a3314dd781a7 100644 --- a/drivers/block/drbd/drbd_int.h +++ b/drivers/block/drbd/drbd_int.h @@ -620,7 +620,7 @@ struct fifo_buffer { unsigned int head_index; unsigned int size; int total; /* sum of all values */ - int values[0]; + int values[]; }; extern struct fifo_buffer *fifo_alloc(unsigned int fifo_size); diff --git a/drivers/block/drbd/drbd_protocol.h b/drivers/block/drbd/drbd_protocol.h index e6fc5ad72501..dea59c92ecc1 100644 --- a/drivers/block/drbd/drbd_protocol.h +++ b/drivers/block/drbd/drbd_protocol.h @@ -271,7 +271,7 @@ struct p_rs_param { u32 resync_rate; /* Since protocol version 88 and higher. */ - char verify_alg[0]; + char verify_alg[]; } __packed; struct p_rs_param_89 { @@ -305,7 +305,7 @@ struct p_protocol { u32 two_primaries; /* Since protocol version 87 and higher. */ - char integrity_alg[0]; + char integrity_alg[]; } __packed; @@ -360,7 +360,7 @@ struct p_sizes { u16 dds_flags; /* use enum dds_flags here. */ /* optional queue_limits if (agreed_features & DRBD_FF_WSAME) */ - struct o_qlim qlim[0]; + struct o_qlim qlim[]; } __packed; struct p_state { @@ -409,7 +409,7 @@ struct p_compressed_bm { */ u8 encoding; - u8 code[0]; + u8 code[]; } __packed; struct p_delay_probe93 {