From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: [patch 072/166] mm/shmem.c: distribute switch variables for initialization Date: Mon, 06 Apr 2020 20:07:51 -0700 Message-ID: <20200407030751.w0w2M3QVA%akpm@linux-foundation.org> References: <20200406200254.a69ebd9e08c4074e41ddebaf@linux-foundation.org> Reply-To: linux-kernel@vger.kernel.org Return-path: Received: from mail.kernel.org ([198.145.29.99]:52896 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726303AbgDGDHw (ORCPT ); Mon, 6 Apr 2020 23:07:52 -0400 In-Reply-To: <20200406200254.a69ebd9e08c4074e41ddebaf@linux-foundation.org> Sender: mm-commits-owner@vger.kernel.org List-Id: mm-commits@vger.kernel.org To: akpm@linux-foundation.org, glider@google.com, hughd@google.com, keescook@chromium.org, linux-mm@kvack.org, mm-commits@vger.kernel.org, torvalds@linux-foundation.org From: Kees Cook Subject: mm/shmem.c: distribute switch variables for initialization Variables declared in a switch statement before any case statements cannot be automatically initialized with compiler instrumentation (as they are not part of any execution flow). With GCC's proposed automatic stack variable initialization feature, this triggers a warning (and they don't get initialized). Clang's automatic stack variable initialization (via CONFIG_INIT_STACK_ALL=y) doesn't throw a warning, but it also doesn't initialize such variables[1]. Note that these warnings (or silent skipping) happen before the dead-store elimination optimization phase, so even when the automatic initializations are later elided in favor of direct initializations, the warnings remain. To avoid these problems, move such variables into the "case" where they're used or lift them up into the main function body. mm/shmem.c: In function `shmem_getpage_gfp': mm/shmem.c:1816:10: warning: statement will never be executed [-Wswitch-unreachable] 1816 | loff_t i_size; | ^~~~~~ [1] https://bugs.llvm.org/show_bug.cgi?id=44916 Link: http://lkml.kernel.org/r/20200220062312.69165-1-keescook@chromium.org Signed-off-by: Kees Cook Reviewed-by: Andrew Morton Cc: Hugh Dickins Cc: Alexander Potapenko Signed-off-by: Andrew Morton --- mm/shmem.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) --- a/mm/shmem.c~shmem-distribute-switch-variables-for-initialization +++ a/mm/shmem.c @@ -1812,17 +1812,20 @@ repeat: if (shmem_huge == SHMEM_HUGE_FORCE) goto alloc_huge; switch (sbinfo->huge) { - loff_t i_size; - pgoff_t off; case SHMEM_HUGE_NEVER: goto alloc_nohuge; - case SHMEM_HUGE_WITHIN_SIZE: + case SHMEM_HUGE_WITHIN_SIZE: { + loff_t i_size; + pgoff_t off; + off = round_up(index, HPAGE_PMD_NR); i_size = round_up(i_size_read(inode), PAGE_SIZE); if (i_size >= HPAGE_PMD_SIZE && i_size >> PAGE_SHIFT >= off) goto alloc_huge; - /* fallthrough */ + + fallthrough; + } case SHMEM_HUGE_ADVISE: if (sgp_huge == SGP_HUGE) goto alloc_huge; _