From: Nathan Chancellor natechancellor@gmail.com
commit 7bf03e7504e433da274963c447648876902b86df upstream.
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.
Closes: https://github.com/ClangBuiltLinux/linux/issues/778 Suggested-by: Michel Dänzer michel@daenzer.net Reviewed-by: Jani Nikula jani.nikula@intel.com Signed-off-by: Nathan Chancellor natechancellor@gmail.com Signed-off-by: Jani Nikula jani.nikula@intel.com Link: https://patchwork.freedesktop.org/patch/msgid/20200214054706.33870-1-natecha... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c @@ -1452,7 +1452,7 @@ static int eb_relocate_vma(struct i915_e
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;
/*