[PATCH AUTOSEL 5.6 012/606] gcc-10: disable 'array-bounds' warning for now

Sasha Levin
2020-06-09T00:42:43Z

From: Linus Torvalds <torvalds@linux-foundation.org>

commit 44720996e2d79e47d508b0abe99b931a726a3197 upstream.

This is another fine warning, related to the 'zero-length-bounds' one,
but hitting the same historical code in the kernel.

Because C didn't historically support flexible array members, we have
code that instead uses a one-sized array, the same way we have cases of
zero-sized arrays.

The one-sized arrays come from either not wanting to use the gcc
zero-sized array extension, or from a slight convenience-feature, where
particularly for strings, the size of the structure now includes the
allocation for the final NUL character.

So with a "char name[1];" at the end of a structure, you can do things
like

v = my_malloc(sizeof(struct vendor) + strlen(name));

and avoid the "+1" for the terminator.

Yes, the modern way to do that is with a flexible array, and using
'offsetof()' instead of 'sizeof()', and adding the "+1" by hand. That
also technically gets the size "more correct" in that it avoids any
alignment (and thus padding) issues, but this is another long-term
cleanup thing that will not happen for 5.7.

So disable the warning for now, even though it's potentially quite
useful. Having a slew of warnings that then hide more urgent new issues
is not an improvement.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
Makefile | 1 +
1 file changed, 1 insertion(+)

diff --git a/Makefile b/Makefile
index b1ce2a7a25b0..e7c2811856f1 100644
--- a/Makefile
+++ b/Makefile
@@ -859,6 +859,7 @@ KBUILD_CFLAGS += $(call cc-disable-warning, stringop-truncation)

# We'll want to enable this eventually, but it's not going away for 5.7 at least
KBUILD_CFLAGS += $(call cc-disable-warning, zero-length-bounds)
+KBUILD_CFLAGS += $(call cc-disable-warning, array-bounds)

# Enabled with W=2, disabled by default as noisy
KBUILD_CFLAGS += $(call cc-disable-warning, maybe-uninitialized)
--
2.25.1