From 60da7d0bc7482a30817c73fdc8152123d19919f8 Mon Sep 17 00:00:00 2001 From: "Gustavo A. R. Silva" Date: Thu, 7 May 2020 14:23:02 -0500 Subject: [PATCH] sparc64: Replace zero-length array with flexible-array 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 Signed-off-by: David S. Miller --- arch/sparc/kernel/cpumap.c | 2 +- arch/sparc/kernel/ds.c | 8 ++++---- 2 files changed, 5 insertions(+), 5 deletions(-) diff --git a/arch/sparc/kernel/cpumap.c b/arch/sparc/kernel/cpumap.c index 1cb62bfeaa1f..f07ea88a83af 100644 --- a/arch/sparc/kernel/cpumap.c +++ b/arch/sparc/kernel/cpumap.c @@ -50,7 +50,7 @@ struct cpuinfo_tree { /* Offsets into nodes[] for each level of the tree */ struct cpuinfo_level level[CPUINFO_LVL_MAX]; - struct cpuinfo_node nodes[0]; + struct cpuinfo_node nodes[]; }; diff --git a/arch/sparc/kernel/ds.c b/arch/sparc/kernel/ds.c index 75232cbd58bf..522e5b51050c 100644 --- a/arch/sparc/kernel/ds.c +++ b/arch/sparc/kernel/ds.c @@ -87,7 +87,7 @@ struct ds_reg_req { __u64 handle; __u16 major; __u16 minor; - char svc_id[0]; + char svc_id[]; }; struct ds_reg_ack { @@ -701,12 +701,12 @@ struct ds_var_hdr { struct ds_var_set_msg { struct ds_var_hdr hdr; - char name_and_value[0]; + char name_and_value[]; }; struct ds_var_delete_msg { struct ds_var_hdr hdr; - char name[0]; + char name[]; }; struct ds_var_resp { @@ -989,7 +989,7 @@ struct ds_queue_entry { struct ds_info *dp; int req_len; int __pad; - u64 req[0]; + u64 req[]; }; static void process_ds_work(void)