svn commit: r357349 - in head/sys: conf modules/tpm

[Dimitry Andric]

On 1 Feb 2020, at 18:55, Ian Lepore <ian at FreeBSD.org> wrote:
> 
> On Fri, 2020-01-31 at 19:36 +0000, Dimitry Andric wrote:
>> Author: dim
>> Date: Fri Jan 31 19:36:14 2020
>> New Revision: 357349
>> URL: https://svnweb.freebsd.org/changeset/base/357349
>> 
>> Log:
>>  Merge r357348 from the clang 10.0.0 import branch:
>> 
>>  Disable new clang 10.0.0 warnings about converting the result of shift
>>  operations to a boolean in tpm(4):
>> 
>>  sys/dev/tpm/tpm_crb.c:301:32: error: converting the result of '<<' to a boolean; did you mean '(1 << (0)) != 0'? [-Werror,-Wint-in-bool-context]
>>          WR4(sc, TPM_CRB_CTRL_CANCEL, !TPM_CRB_CTRL_CANCEL_CMD);
>>                                        ^
>>  sys/dev/tpm/tpm_crb.c:73:34: note: expanded from macro 'TPM_CRB_CTRL_CANCEL_CMD'
>>  #define TPM_CRB_CTRL_CANCEL_CMD         BIT(0)
>>                                          ^
>>  sys/dev/tpm/tpm20.h:60:19: note: expanded from macro 'BIT'
>>  #define BIT(x) (1 << (x))
>>                    ^
>> 
>>  Such warnings can be useful in C++ contexts, but not so much in kernel
>>  drivers, where this type of bit twiddling is commonplace.  So disable it
>>  for this case.
>> 
> 
> I think the point of the compiler warning about shift in a boolean
> context is the same as warning about assignment in a boolean
> context.  I.e,
> 
>   if (a << 3)
> 
> might be a typo for
> 
>   if (a < 3)
> 
> in the same way as "a = 3" might have been intended to be "a == 3".

Yes, clang inherited this warning from gcc, where it says in:
https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wint-in-bool-context

-Wint-in-bool-context
  Warn for suspicious use of integer values where boolean values are
  expected, such as conditional expressions (?:) using non-boolean
  integer constants in boolean context, like if (a <= b ? 2 : 3). Or
  left shifting of signed integers in boolean context, like for (a = 0;
  1 << a; a++);. Likewise for all kinds of multiplications regardless of
  the data type. This warning is enabled by -Wall.

-Dimitry

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