On Thu, 13 Feb 2020, Nathan Chancellor <natechancellor@xxxxxxxxx> wrote: > A recent commit in clang added -Wtautological-compare to -Wall, which is > enabled for i915 after -Wtautological-compare is disabled for the rest > of the kernel so we see the following warning on x86_64: > > ../drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c:1433:22: 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))) > ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~ > ../include/linux/compiler.h:78:42: note: expanded from macro 'unlikely' > # define unlikely(x) __builtin_expect(!!(x), 0) > ^ > 1 warning generated. > > It is not wrong in the case where ULONG_MAX > UINT_MAX but it does not > account for the case where this file is built for 32-bit x86, where > ULONG_MAX == UINT_MAX and this check is still relevant. > > Cast remain to unsigned long, which keeps the generated code the same > (verified with clang-11 on x86_64 and GCC 9.2.0 on x86 and x86_64) and > the warning is silenced so we can catch more potential issues in the > future. > > Link: https://github.com/ClangBuiltLinux/linux/issues/778 > Suggested-by: Michel Dänzer <michel@xxxxxxxxxxx> > Signed-off-by: Nathan Chancellor <natechancellor@xxxxxxxxx> Works for me as a workaround, Reviewed-by: Jani Nikula <jani.nikula@xxxxxxxxx> > --- > > Round 3 :) > > Previous threads/patches: > > https://lore.kernel.org/lkml/20191123195321.41305-1-natechancellor@xxxxxxxxx/ > https://lore.kernel.org/lkml/20200211050808.29463-1-natechancellor@xxxxxxxxx/ > > drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c > index 60c984e10c4a..47f4d8ab281e 100644 > --- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c > +++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c > @@ -1430,7 +1430,7 @@ static int eb_relocate_vma(struct i915_execbuffer *eb, struct i915_vma *vma) > > urelocs = u64_to_user_ptr(entry->relocs_ptr); > remain = entry->relocation_count; > - if (unlikely(remain > N_RELOC(ULONG_MAX))) > + if (unlikely((unsigned long)remain > N_RELOC(ULONG_MAX))) > return -EINVAL; > > /* -- Jani Nikula, Intel Open Source Graphics Center _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
