From 660e899103e29aabcc05447ab20684811ea86107 Mon Sep 17 00:00:00 2001 From: Vincent Mailhol Date: Sat, 20 Dec 2025 12:02:19 +0100 Subject: [PATCH] kbuild: remove gcc's -Wtype-limits W=2 builds are heavily polluted by the -Wtype-limits warning. Here are some W=12 statistics on Linux v6.19-rc1 for an x86_64 defconfig (with just CONFIG_WERROR set to "n") using gcc 14.3.1: Warning name count percent ------------------------------------------------- -Wlogical-op 2 0.00 % -Wmaybe-uninitialized 138 0.20 % -Wunused-macros 869 1.24 % -Wmissing-field-initializers 1418 2.02 % -Wshadow 2234 3.19 % -Wtype-limits 65378 93.35 % ------------------------------------------------- Total 70039 100.00 % As we can see, -Wtype-limits represents the vast majority of all warnings. The reason behind this is that these warnings appear in some common header files, meaning that some unique warnings are repeated tens of thousands of times (once per header inclusion). Add to this the fact that each warning is coupled with a dozen lines detailing some macro expansion. The end result is that the W=2 output is just too bloated and painful to use. Three years ago, I proposed in [1] modifying one such header to silence that noise. Because the code was not faulty, Linus rejected the idea and instead suggested simply removing that warning. At that time, I could not bring myself to send such a patch because, despite its problems, -Wtype-limits would still catch the below bug: unsigned int ret; ret = check(); if (ret < 0) error(); Meanwhile, based on another suggestion from Linus, I added a new check to sparse [2] that would catch the above bug without the useless spam. With this, remove gcc's -Wtype-limits. People who still want to catch incorrect comparisons between unsigned integers and zero can now use sparse instead. On a side note, clang also has a -Wtype-limits warning but: * it is not enabled in the kernel at the moment because, contrary to gcc, clang did not include it under -Wextra. * it does not warn if the code results from a macro expansion. So, if activated, it would not cause as much spam as gcc does. * -Wtype-limits is split into four sub-warnings [3] meaning that if it were to be activated, we could select which one to keep. So there is no present need to explicitly disable -Wtype-limits in clang. [1] linux/bits.h: GENMASK_INPUT_CHECK: reduce W=2 noise by 31% treewide Link: https://lore.kernel.org/all/20220308141201.2343757-1-mailhol.vincent@wanadoo.fr/ [2] Warn about "unsigned value that used to be signed against zero" Link: https://lore.kernel.org/all/20250921061337.3047616-1-mailhol@kernel.org/ [3] clang's -Wtype-limits Link: https://clang.llvm.org/docs/DiagnosticsReference.html#wtype-limits Reviewed-by: Nicolas Schier Signed-off-by: Vincent Mailhol Link: https://patch.msgid.link/20251220-remove_wtype-limits-v3-1-24b170af700e@kernel.org Signed-off-by: Nathan Chancellor --- scripts/Makefile.warn | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/scripts/Makefile.warn b/scripts/Makefile.warn index 68e6fafcb80c8..c593ab1257de0 100644 --- a/scripts/Makefile.warn +++ b/scripts/Makefile.warn @@ -55,6 +55,9 @@ else KBUILD_CFLAGS += -Wno-main endif +# Too noisy on range checks and in macros handling both signed and unsigned. +KBUILD_CFLAGS += -Wno-type-limits + # These result in bogus false positives KBUILD_CFLAGS += $(call cc-option, -Wno-dangling-pointer) @@ -174,7 +177,6 @@ else # The following turn off the warnings enabled by -Wextra KBUILD_CFLAGS += -Wno-missing-field-initializers -KBUILD_CFLAGS += -Wno-type-limits KBUILD_CFLAGS += -Wno-shift-negative-value ifdef CONFIG_CC_IS_CLANG -- 2.47.3