Re: [edk2-devel] [PATCH] BaseTools/tools_def: Disable unneeded-internal-declaration warning in CLANGPDB

["Laszlo Ersek" <lersek@redhat.com>]

On 12/11/23 16:18, Mike Beaton wrote:
> I believe this would be logically wrong, as the other versions still
> wouldn't compile if you changed the relevant debug Pcds. (Which are
> logically independent of the compile and link options - e.g. what if for
> some reason you wanted to single step with the Debug Pcds set to
> disabled, in a NOOPT build?)

I don't think that use case exists in practice.

Anyway, my suggestion is based on prior art: I *think* we ask gcc to
whine about unused local variables in RELEASE builds only, too. See
commits 20d00edf21d2 ("BaseTools/GCC: set -Wno-unused-but-set-variables
only on RELEASE builds", 2016-03-25) and 8b6366f87584 ("BaseTools/GCC:
set -Wno-unused-const-variable on RELEASE builds", 2017-09-08).

... TBH I don't understand the current state of
"-Wno-unused-but-set-variables" and "-Wno-unused-const-variable" between
X64 and AARCH64, considering the DEBUG target. Today,
DEBUG_GCC5_AARCH64_CC_FLAGS disables these warnings, but
DEBUG_GCC5_X64_CC_FLAGS doesn't, even though *both* macros specify
-flto. Compare commit 06c8a34cc4bc ("BaseTool/tools_def GCC5: enable
optimization for ARM/AARCH64 DEBUG builds", 2017-12-08) -- I don't
understand why "-flto" had to be accompanied by
"-Wno-unused-but-set-variable -Wno-unused-const-variable" in that commit.

In brief, IA32 and X64 prior art supports my suggestion to shut up the
warning only for RELEASE (for CLANGPDB too), but ARM/AARCH64 prior art
contradicts that proposal. IOW, prior art is inconsistent per se... I
don't understand.

Laszlo

> On Mon, 11 Dec 2023, 15:00 Laszlo Ersek, <lersek@redhat.com
> <mailto:lersek@redhat.com>> wrote:
> 
>     On 12/10/23 11:18, Mike Beaton wrote:
>     > From: Mike Beaton <mjsbeaton@gmail.com <mailto:mjsbeaton@gmail.com>>
>     >
>     > This warning was already disabled in CLANGDWARF by commit
>     > d3225577123767fd09c91201d27e9c91663ae132.
>     >
>     > gcc can distinguish between optimised-away variable usage (as  can
>     occur in
>     > valid debug code) and genuinely unused variables, and only
>     complains about
>     > the latter. clang cannot, and therefore this warning ends up
>     complaining
>     > about valid debug code under clang.
>     >
>     > Since EDK-II code is in general going to be compiled by gcc as
>     well as clang
>     > then disabling this warning in clang does not amount to entirely
>     removing
>     > potentially valid warnings about genuinely unused variables.
>     >
>     > Signed-off-by: Mike Beaton <mjsbeaton@gmail.com
>     <mailto:mjsbeaton@gmail.com>>
>     > ---
>     >  BaseTools/Conf/tools_def.template | 2 +-
>     >  1 file changed, 1 insertion(+), 1 deletion(-)
>     >
>     > diff --git a/BaseTools/Conf/tools_def.template
>     b/BaseTools/Conf/tools_def.template
>     > index c34ecfd557..48cf45245f 100755
>     > --- a/BaseTools/Conf/tools_def.template
>     > +++ b/BaseTools/Conf/tools_def.template
>     > @@ -1754,7 +1754,7 @@ DEFINE CLANGPDB_X64_PREFIX           =
>     ENV(CLANG_BIN)
>     >  DEFINE CLANGPDB_IA32_TARGET          = -target
>     i686-unknown-windows-gnu
>     >  DEFINE CLANGPDB_X64_TARGET           = -target
>     x86_64-unknown-windows-gnu
>     > 
>     > -DEFINE CLANGPDB_WARNING_OVERRIDES    = -Wno-parentheses-equality
>     -Wno-tautological-compare
>     -Wno-tautological-constant-out-of-range-compare -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-microsoft-enum-forward-reference
>     > +DEFINE CLANGPDB_WARNING_OVERRIDES    = -Wno-parentheses-equality
>     -Wno-tautological-compare
>     -Wno-tautological-constant-out-of-range-compare -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
>     -Wno-microsoft-enum-forward-reference
>     >  DEFINE CLANGPDB_ALL_CC_FLAGS         = DEF(GCC48_ALL_CC_FLAGS)
>     DEF(CLANGPDB_WARNING_OVERRIDES) -fno-stack-protector -funsigned-char
>     -ftrap-function=undefined_behavior_has_been_optimized_away_by_clang
>     -Wno-address -Wno-shift-negative-value -Wno-unknown-pragmas
>     -Wno-incompatible-library-redeclaration -Wno-null-dereference
>     -mno-implicit-float -mms-bitfields -mno-stack-arg-probe -nostdlib
>     -nostdlibinc -fseh-exceptions
>     > 
>     >  ###########################
> 
>     AFAICT, CLANGPDB_WARNING_OVERRIDES gets included in
>     CLANGPDB_ALL_CC_FLAGS, which in turn gets included in all three of
>     DEBUG, RELEASE and NOOPT build target flags.
> 
>     The original report was "RELEASE CLANGPDB OVMF currently does not
>     compile".
> 
>     Can we use "-Wno-unneeded-internal-declaration" with RELEASE builds
>     only?
> 
>     Thanks,
>     Laszlo
> 



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