From 27d80fa24326b7b33c8ee7527843776e5df808a7 Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Mon, 6 Apr 2020 20:07:51 -0700 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 Signed-off-by: Kees Cook Signed-off-by: Andrew Morton Reviewed-by: Andrew Morton Cc: Hugh Dickins Cc: Alexander Potapenko Link: http://lkml.kernel.org/r/20200220062312.69165-1-keescook@chromium.org Signed-off-by: Linus Torvalds --- mm/shmem.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) (limited to 'mm') diff --git a/mm/shmem.c b/mm/shmem.c index 2c255f383608..97448a46a4dc 100644 --- a/mm/shmem.c +++ b/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; -- cgit