Re: [PATCH v1 18/19] ArmPlatformPkg: Fix comparison of constants warning

["Ard Biesheuvel" <ard.biesheuvel@linaro.org>]

On Thu, 21 Nov 2019 at 13:35, Leif Lindholm <leif.lindholm@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.mujawar@arm.com>
>
> Reviewed-by: Leif Lindholm <leif.lindholm@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.


> > ---
> >  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)'
> >
> >