From 8ac7571a8cd3c11da24c3c3555f6e40e33049609 Mon Sep 17 00:00:00 2001 From: Gustavo A. R. Silva Date: Mon, 11 May 2020 15:09:11 -0500 Subject: perf/x86: 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: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20200511200911.GA13149@embeddedor --- arch/x86/events/intel/bts.c | 2 +- arch/x86/events/intel/uncore.h | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/x86/events/intel/bts.c b/arch/x86/events/intel/bts.c index 6a3b599ee0fe..731dd8d0dbb1 100644 --- a/arch/x86/events/intel/bts.c +++ b/arch/x86/events/intel/bts.c @@ -58,7 +58,7 @@ struct bts_buffer { local_t head; unsigned long end; void **data_pages; - struct bts_phys buf[0]; + struct bts_phys buf[]; }; static struct pmu bts_pmu; diff --git a/arch/x86/events/intel/uncore.h b/arch/x86/events/intel/uncore.h index 0da4a4605536..b469ddd45515 100644 --- a/arch/x86/events/intel/uncore.h +++ b/arch/x86/events/intel/uncore.h @@ -130,7 +130,7 @@ struct intel_uncore_box { struct list_head list; struct list_head active_list; void __iomem *io_addr; - struct intel_uncore_extra_reg shared_regs[0]; + struct intel_uncore_extra_reg shared_regs[]; }; /* CFL uncore 8th cbox MSRs */ -- cgit v1.2.3