[PATCH v2] stmmac: avoid ipq806x constant overflow warning
geert at linux-m68k.org
Fri Nov 13 00:00:26 PST 2015
On Fri, Nov 13, 2015 at 8:52 AM, Joe Perches <joe at perches.com> wrote:
> 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.
I only recently started liking the BIT() macro (before I preferred hex, too).
Perhaps because Renesas datasheets use bit numbers all over the place ;-)
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
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