On Fri, 2015-11-13 at 08:37 +0100, Geert Uytterhoeven wrote: > On Thu, Nov 12, 2015 at 10:03 PM, Arnd Bergmann <a...@arndb.de> > wrote: > > Building dwmac-ipq806x on a 64-bit architecture produces a harmless > > warning from gcc: > > > > stmmac/dwmac-ipq806x.c: In function 'ipq806x_gmac_probe': > > include/linux/bitops.h:6:19: warning: overflow in implicit constant > > conversion [-Woverflow] > > val = QSGMII_PHY_CDR_EN | > > stmmac/dwmac-ipq806x.c:333:8: note: in expansion of macro > > 'QSGMII_PHY_CDR_EN' > > #define QSGMII_PHY_CDR_EN BIT(0) > > #define BIT(nr) (1UL << (nr)) > > > > This is a result of the type conversion rules in C, when we take > > the > > logical OR of multiple different types. In particular, we have > > and unsigned long > > > > QSGMII_PHY_CDR_EN == BIT(0) == (1ul << 0) == > > 0x0000000000000001ul > > > > and a signed int > > > > 0xC << QSGMII_PHY_TX_DRV_AMP_OFFSET == 0xc0000000 > > > > which together gives a signed long value > > > > 0xffffffffc0000001l > > > > and when this is passed into a function that takes an unsigned int > > type, > > gcc warns about the signed overflow and the loss of the upper 32 > > -bits that > > are all ones. > > > > This patch adds 'ul' type modifiers to the literal numbers passed > > in > > here, so now the expression remains an 'unsigned long' with the > > upper > > bits all zero, and that avoids the signed overflow and the warning. > > FWIW, the 64-bitness of BIT() on 64-bit platforms is also causing > subtle > warnings in other places, e.g. when inverting them to create bit > mask, cfr. > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commi > t/?id=a9efeca613a8fe5281d7c91f5c8c9ea46f2312f6 > > Gr{oetje,eeting}s,
I still think specific length BIT macros can be useful. https://lkml.org/lkml/2015/10/16/852 -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
