[PATCH] drm/i915: Disable -Wtautological-constant-out-of-range-compare

Nathan Chancellor
2020-02-11T07:26:20Z

A recent commit in clang added -Wtautological-compare to -Wall, which is
enabled for i915 so we see the following warning:

../drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c:1485:22: warning:
result of comparison of constant 576460752303423487 with expression of
type 'unsigned int' is always false
[-Wtautological-constant-out-of-range-compare]
if (unlikely(remain > N_RELOC(ULONG_MAX)))
~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~

This warning only happens on x86_64 but that check is relevant for
32-bit x86 so we cannot remove it. -Wtautological-compare on a whole has
good warnings but this one is not really relevant for the kernel because
of all of the different configurations that are used to build the
kernel. When -Wtautological-compare is enabled for the kernel, this
option will remain disabled so do that for i915 now.

Link: https://github.com/ClangBuiltLinux/linux/issues/778
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
---
drivers/gpu/drm/i915/Makefile | 1 +
1 file changed, 1 insertion(+)

diff --git a/drivers/gpu/drm/i915/Makefile b/drivers/gpu/drm/i915/Makefile
index 38df01c23176..55dbcca179c7 100644
--- a/drivers/gpu/drm/i915/Makefile
+++ b/drivers/gpu/drm/i915/Makefile
@@ -21,6 +21,7 @@ subdir-ccflags-y += $(call cc-disable-warning, unused-but-set-variable)
subdir-ccflags-y += $(call cc-disable-warning, sign-compare)
subdir-ccflags-y += $(call cc-disable-warning, sometimes-uninitialized)
subdir-ccflags-y += $(call cc-disable-warning, initializer-overrides)
+subdir-ccflags-y += $(call cc-disable-warning, tautological-constant-out-of-range-compare)
subdir-ccflags-$(CONFIG_DRM_I915_WERROR) += -Werror

# Fine grained warnings disable
--
2.25.0