From d5d45a7f26194460964eb5677a9226697f7b7fdd Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Sun, 20 Apr 2025 10:33:23 -0700 Subject: [PATCH] gcc-15: make 'unterminated string initialization' just a warning MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit gcc-15 enabling -Wunterminated-string-initialization in -Wextra by default was done with the best intentions, but the warning is still quite broken. What annoys me about the warning is that this is a very traditional AND CORRECT way to initialize fixed byte arrays in C: unsigned char hex[16] = "0123456789abcdef"; and we use this all over the kernel. And the warning is fine, but gcc developers apparently never made a reasonable way to disable it. As is (sadly) tradition with these things. Yes, there's "__attribute__((nonstring))", and we have a macro to make that absolutely disgusting syntax more palatable (ie the kernel syntax for that monstrosity is just "__nonstring"). But that attribute is misdesigned. What you'd typically want to do is tell the compiler that you are using a type that isn't a string but a byte array, but that doesn't work at all: warning: ‘nonstring’ attribute does not apply to types [-Wattributes] and because of this fundamental mis-design, you then have to mark each instance of that pattern. This is particularly noticeable in our ACPI code, because ACPI has this notion of a 4-byte "type name" that gets used all over, and is exactly this kind of byte array. This is a sad oversight, because the warning is useful, but really would be so much better if gcc had also given a sane way to indicate that we really just want a byte array type at a type level, not the broken "each and every array definition" level. So now instead of creating a nice "ACPI name" type using something like typedef char acpi_name_t[4] __nonstring; we have to do things like char name[ACPI_NAMESEG_SIZE] __nonstring; in every place that uses this concept and then happens to have the typical initializers. This is annoying me mainly because I think the warning _is_ a good warning, which is why I'm not just turning it off in disgust. But it is hampered by this bad implementation detail. [ And obviously I'm doing this now because system upgrades for me are something that happen in the middle of the release cycle: don't do it before or during travel, or just before or during the busy merge window period. ] Signed-off-by: Linus Torvalds --- Makefile | 3 +++ 1 file changed, 3 insertions(+) diff --git a/Makefile b/Makefile index e65f8735c7bf..0a9992db4fe0 100644 --- a/Makefile +++ b/Makefile @@ -1056,6 +1056,9 @@ KBUILD_CFLAGS += $(call cc-option, -fstrict-flex-arrays=3) KBUILD_CFLAGS-$(CONFIG_CC_NO_STRINGOP_OVERFLOW) += $(call cc-option, -Wno-stringop-overflow) KBUILD_CFLAGS-$(CONFIG_CC_STRINGOP_OVERFLOW) += $(call cc-option, -Wstringop-overflow) +#Currently, disable -Wunterminated-string-initialization as an error +KBUILD_CFLAGS += $(call cc-option, -Wno-error=unterminated-string-initialization) + # disable invalid "can't wrap" optimizations for signed / pointers KBUILD_CFLAGS += -fno-strict-overflow -- 2.49.0