[PATCH] asm-generic: fix -Wtype-limits compiler warnings

Qian Cai
2019-07-23T20:50:24Z

The commit d66acc39c7ce ("bitops: Optimise get_order()") introduced a
compilation warning because "rx_frag_size" is an "ushort" while
PAGE_SHIFT here is 16. The commit changed the get_order() to be a
multi-line macro where compilers insist to check all statements in the
macro even when __builtin_constant_p(rx_frag_size) will return false as
"rx_frag_size" is a module parameter.

In file included from ./arch/powerpc/include/asm/page_64.h:107,
from ./arch/powerpc/include/asm/page.h:242,
from ./arch/powerpc/include/asm/mmu.h:132,
from ./arch/powerpc/include/asm/lppaca.h:47,
from ./arch/powerpc/include/asm/paca.h:17,
from ./arch/powerpc/include/asm/current.h:13,
from ./include/linux/thread_info.h:21,
from ./arch/powerpc/include/asm/processor.h:39,
from ./include/linux/prefetch.h:15,
from drivers/net/ethernet/emulex/benet/be_main.c:14:
drivers/net/ethernet/emulex/benet/be_main.c: In function
'be_rx_cqs_create':
./include/asm-generic/getorder.h:54:9: warning: comparison is always
true due to limited range of data type [-Wtype-limits]
(((n) < (1UL << PAGE_SHIFT)) ? 0 : \
^
drivers/net/ethernet/emulex/benet/be_main.c:3138:33: note: in expansion
of macro 'get_order'
adapter->big_page_size = (1 << get_order(rx_frag_size)) * PAGE_SIZE;
^~~~~~~~~

Fix it by moving almost all of this multi-line macro into a proper
function __get_order(), and leave get_order() as a single-line macro in
order to avoid compilation errors.

Fixes: d66acc39c7ce ("bitops: Optimise get_order()")
Signed-off-by: Qian Cai <cai@lca.pw>
---
include/asm-generic/getorder.h | 15 ++++++++++-----
1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/include/asm-generic/getorder.h b/include/asm-generic/getorder.h
index c64bea7a52be..c6a6d3cd7007 100644
--- a/include/asm-generic/getorder.h
+++ b/include/asm-generic/getorder.h
@@ -15,6 +15,16 @@ int __get_order(unsigned long size)
{
int order;

+ if (__builtin_constant_p(size)) {
+ if (!size)
+ return BITS_PER_LONG - PAGE_SHIFT;
+
+ if (size < (1UL << PAGE_SHIFT))
+ return 0;
+
+ return ilog2((size) - 1) - PAGE_SHIFT + 1;
+ }
+
size--;
size >>= PAGE_SHIFT;
#if BITS_PER_LONG == 32
@@ -49,11 +59,6 @@ int __get_order(unsigned long size)
*/
#define get_order(n) \
( \
- __builtin_constant_p(n) ? ( \
- ((n) == 0UL) ? BITS_PER_LONG - PAGE_SHIFT : \
- (((n) < (1UL << PAGE_SHIFT)) ? 0 : \
- ilog2((n) - 1) - PAGE_SHIFT + 1) \
- ) : \
__get_order(n) \
)

--
1.8.3.1