Re: [edk2-devel] [PATCH V2] DebugLib: Allow -Wunneeded-internal-declaration with clang

["Mike Beaton" <mjsbeaton@gmail.com>]

On Tue, 12 Dec 2023 at 21:45, <mjsbeaton@gmail.com> wrote:
>
> From: Mikhail Krichanov <mikhailkrichanov@gmail.com>
>
> Provides a variant of the DEBUG macro for clang when MDEPKG_NDEBUG is
> defined, which uses but discards the contained expression. This means
> clang can tell that it has optimised away variable usage as part of
> valid debug patterns (such as a STATIC variable which is only used in
> DEBUG statements) - rather than just seeing such variables as
> completely unused - therefore we can keep
> -Wunneeded-internal-declaration (as part of -Wall) to warn about
> mistakenly genuinely unused variables elsewhere.
>
> Note that the _Pragma in the clang/gcc variant is to temporarily
> suppress the warning about `(VOID) Expression;`, whilst the presence
> of `(VOID) Expression;` (once allowed) is what prevents the unwanted
> warning about unneeded variables.
>
> Signed-off-by: Mikhail Krichanov <mikhailkrichanov@gmail.com>
> Signed-off-by: Mike Beaton <mjsbeaton@gmail.com>
> ---
>  BaseTools/Conf/tools_def.template |  2 +-
>  MdePkg/Include/Library/DebugLib.h | 10 ++++++++++
>  2 files changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/BaseTools/Conf/tools_def.template b/BaseTools/Conf/tools_def.template
> index c34ecfd557..eaccf0b698 100755
> --- a/BaseTools/Conf/tools_def.template
> +++ b/BaseTools/Conf/tools_def.template
> @@ -1859,7 +1859,7 @@ DEFINE CLANGDWARF_X64_DLINK2_FLAGS        = -Wl,--defsym=PECOFF_HEADER_SIZE=0x22
>  DEFINE CLANGDWARF_IA32_TARGET             = -target i686-pc-linux-gnu
>  DEFINE CLANGDWARF_X64_TARGET              = -target x86_64-pc-linux-gnu
>
> -DEFINE CLANGDWARF_WARNING_OVERRIDES    = -Wno-parentheses-equality -Wno-empty-body -Wno-unused-const-variable -Wno-varargs -Wno-unknown-warning-option -Wno-unused-but-set-variable -Wno-unused-const-variable -Wno-unaligned-access -Wno-unneeded-internal-declaration
> +DEFINE CLANGDWARF_WARNING_OVERRIDES    = -Wno-parentheses-equality -Wno-empty-body -Wno-unused-const-variable -Wno-varargs -Wno-unknown-warning-option -Wno-unused-but-set-variable -Wno-unused-const-variable -Wno-unaligned-access
>  DEFINE CLANGDWARF_ALL_CC_FLAGS         = DEF(GCC48_ALL_CC_FLAGS) DEF(CLANGDWARF_WARNING_OVERRIDES) -fno-stack-protector -mms-bitfields -Wno-address -Wno-shift-negative-value -Wno-unknown-pragmas -Wno-incompatible-library-redeclaration -fno-asynchronous-unwind-tables -mno-sse -mno-mmx -msoft-float -mno-implicit-float  -ftrap-function=undefined_behavior_has_been_optimized_away_by_clang -funsigned-char -fno-ms-extensions -Wno-null-dereference
>
>  ###########################
> diff --git a/MdePkg/Include/Library/DebugLib.h b/MdePkg/Include/Library/DebugLib.h
> index 40772f2e0f..7368004f46 100644
> --- a/MdePkg/Include/Library/DebugLib.h
> +++ b/MdePkg/Include/Library/DebugLib.h
> @@ -425,6 +425,16 @@ UnitTestDebugAssert (
>          _DEBUG (Expression);       \
>        }                            \
>      } while (FALSE)
> +#elif defined (__GNUC__) || defined (__clang__)
> +#define DEBUG(Expression)                                \
> +    do {                                                   \
> +      _Pragma("GCC diagnostic push")                       \
> +      _Pragma("GCC diagnostic ignored \"-Wunused-value\"") \
> +      if ((FALSE)) {                                       \
> +        (VOID) Expression;                                 \
> +      }                                                    \
> +      _Pragma("GCC diagnostic pop")                        \
> +    } while (FALSE)
>  #else
>  #define DEBUG(Expression)
>  #endif
> --
> 2.39.2
>

Hi Mikhail,

Are you okay to reply confirming that you're happy with your
Signed-off-by in the above?

Thanks,
Mike


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