[PATCH v2] stmmac: avoid ipq806x constant overflow warning
joe at perches.com
Thu Nov 12 23:52:46 PST 2015
On Fri, 2015-11-13 at 08:37 +0100, Geert Uytterhoeven wrote:
> On Thu, Nov 12, 2015 at 10:03 PM, Arnd Bergmann <arnd at arndb.de>
> > 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
> warnings in other places, e.g. when inverting them to create bit
> mask, cfr.
I still think specific length BIT macros
can be useful.
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