From 914a1951d88968371c7d43400c9d936382cd7d69 Mon Sep 17 00:00:00 2001 From: "Gustavo A. R. Silva" Date: Thu, 7 May 2020 14:05:44 -0500 Subject: [PATCH] PCI: 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 as 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") Link: https://lore.kernel.org/r/20200507190544.GA15633@embeddedor Signed-off-by: Gustavo A. R. Silva Signed-off-by: Bjorn Helgaas --- drivers/pci/pci.c | 2 +- include/linux/pci.h | 4 ++-- 2 files changed, 3 insertions(+), 3 deletions(-) diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c index 595fcf59843f..bb78f580814e 100644 --- a/drivers/pci/pci.c +++ b/drivers/pci/pci.c @@ -1578,7 +1578,7 @@ EXPORT_SYMBOL(pci_restore_state); struct pci_saved_state { u32 config_space[16]; - struct pci_cap_saved_data cap[0]; + struct pci_cap_saved_data cap[]; }; /** diff --git a/include/linux/pci.h b/include/linux/pci.h index 83ce1cdf5676..0453ee458ab1 100644 --- a/include/linux/pci.h +++ b/include/linux/pci.h @@ -279,7 +279,7 @@ struct pci_cap_saved_data { u16 cap_nr; bool cap_extended; unsigned int size; - u32 data[0]; + u32 data[]; }; struct pci_cap_saved_state { @@ -532,7 +532,7 @@ struct pci_host_bridge { resource_size_t start, resource_size_t size, resource_size_t align); - unsigned long private[0] ____cacheline_aligned; + unsigned long private[] ____cacheline_aligned; }; #define to_pci_host_bridge(n) container_of(n, struct pci_host_bridge, dev) -- 2.17.1