On Thu, 21 Nov 2019 at 13:53, Leif Lindholm <leif.lindh...@linaro.org> wrote:
>
> On Thu, Nov 21, 2019 at 13:39:55 +0100, Ard Biesheuvel wrote:
> > On Thu, 21 Nov 2019 at 13:35, Leif Lindholm <leif.lindh...@linaro.org>
> > wrote:
> > >
> > > On Fri, Aug 23, 2019 at 11:55:38 +0100, Sami Mujawar wrote:
> > > > The VS2017 compiler reports 'warning C6326: potential
> > > > comparison of a constant with another constant' when
> > > > a fixed PCD value is compared with a constant value.
> > > >
> > > > The faulting code is as marked by '-->' below:
> > > >
> > > > --> if (FixedPcdGet32 (PL011UartInteger) != 0) {
> > > > Integer = FixedPcdGet32 (PL011UartInteger);
> > > > Fractional = FixedPcdGet32 (PL011UartFractional);
> > > > } else {
> > > > ...
> > > >
> > > > The macro FixedPcdGet32 (PL011UartInteger) evaluates
> > > > to a macro _PCD_VALUE_PL011UartInteger that is defined
> > > > by the build system to represent the UART Integer
> > > > value. Therefore, the VS2017 compiler reports the above
> > > > warning.
> > > >
> > > > Fix this warning by enclosing the code in appropriate
> > > > #if .. #else .. #endif directives.
> > > >
> > > > Signed-off-by: Sami Mujawar <sami.muja...@arm.com>
> > >
> > > Reviewed-by: Leif Lindholm <leif.lindh...@linaro.org>
> > >
> >
> > I don't like this at all.
> >
> > If two expressions happen to evaluate to the same constant, we should
> > be able to compare them using C code.
> >
> > I think we should disable the warning instead.
>
> I agree with that as a general rule, and agree that disabling the
> warning may be preferable in other contexts.
>
> But I somewhat disagree with referring to *this instance* as two
> expressions evaluating to the same constant. This is entirely a
> preprocessor event, somewhat obscured by the Pcd syntax.
> The test is "has the default baudrate been requested or has a specific
> one been requested?".
>
That may be true, but moving from C conditionals to CPP conditionals
obscures the code, and reduces test coverage, so I think it should be
avoided when possible.
> Now, that might be more cleanly described as a macro than inline like
> this - but I think the compiler has usefully warned us about weirdly
> written code. So I would really not want to disable the warning on a
> global level, and would prefer not to do so here.
>
> /
> Leif
>
> >
> > > > ---
> > > > ArmPlatformPkg/Library/PL011UartLib/PL011UartLib.c | 6 +++---
> > > > 1 file changed, 3 insertions(+), 3 deletions(-)
> > > >
> > > > diff --git a/ArmPlatformPkg/Library/PL011UartLib/PL011UartLib.c
> > > > b/ArmPlatformPkg/Library/PL011UartLib/PL011UartLib.c
> > > > index
> > > > 2d3c279cce49304959953ec4a34b50e09a7d0045..dabf099b9bc82e1fb1bd5a2eae3fa4b5878a9e07
> > > > 100644
> > > > --- a/ArmPlatformPkg/Library/PL011UartLib/PL011UartLib.c
> > > > +++ b/ArmPlatformPkg/Library/PL011UartLib/PL011UartLib.c
> > > > @@ -174,10 +174,10 @@ PL011UartInitializePort (
> > > > //
> > > >
> > > > // If PL011 Integer value has been defined then always ignore the
> > > > BAUD rate
> > > > - if (FixedPcdGet32 (PL011UartInteger) != 0) {
> > > > +#if (FixedPcdGet32 (PL011UartInteger) != 0)
> > > > Integer = FixedPcdGet32 (PL011UartInteger);
> > > > Fractional = FixedPcdGet32 (PL011UartFractional);
> > > > - } else {
> > > > +#else
> > > > // If BAUD rate is zero then replace it with the system default
> > > > value
> > > > if (*BaudRate == 0) {
> > > > *BaudRate = FixedPcdGet32 (PcdSerialBaudRate);
> > > > @@ -197,7 +197,7 @@ PL011UartInitializePort (
> > > > Divisor = (UINT32)DivisorValue;
> > > > Integer = Divisor >> FRACTION_PART_SIZE_IN_BITS;
> > > > Fractional = Divisor & FRACTION_PART_MASK;
> > > > - }
> > > > +#endif
> > > >
> > > > //
> > > > // If PL011 is already initialized, check the current settings
> > > > --
> > > > 'Guid(CE165669-3EF3-493F-B85D-6190EE5B9759)'
> > > >
> > > >
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