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Thomas Lamprecht 8b6366f875 BaseTools/GCC: set -Wno-unused-const-variable on RELEASE builds 
TianoCore BZ#700 [1]

Set the '-Wno-unused-const-variables' in RELEASE builds with the
GGC49 and GCC5 toolchain.

This fixes the RELEASE build of OVMF with GCC in version 6 or newer.
GCC 6 added the '-Wunused-const-variable' warning, which gets
activated by '-Wunused-variable' and has the following behavior:
"Warn whenever a constant static variable is unused aside from its
declaration" [2]

Commit 2ad6ba80a1 introduced a case
where exactly this happens on a RELEASE build. All uses of the static
const variable are located in debug code only, which gets thrown out
by the compiler on RELEASE builds and thus triggers the
unused-const-variable warning.

There is currently no GCC 6 toolchain target defined and doing so
would add a lot of boilerplate code. Instead, use the fact that GCC
ignores unknown '-Wno-*' options:

"[...] if the -Wno- form is used [...] no diagnostic is produced for
-Wno-unknown-warning unless other diagnostics are being produced"

This behavior is available in GCC 4.9 [3] (and also earlier, for that
matter), so add the flag to the GCC49 and GCC5 toolchain, even if
both GCC versions do not supports it.
GCC49 doesn't enables LTO whereas GCC5 does. As GCC 6.0 through 6.2
had bugs relating to LTO there can be desire to use the GCC49 target
even if compiling with GCC 6, see 432f1d83f7.

Orient the changes on 20d00edf21 which moved the
'-Wno-unused-but-set-variable' flag to RELEASE builds only, as there
it ensure that it does not gets raised if the only usage of a
variable is in (then collapsed) debug code.

[1] https://bugzilla.tianocore.org/show_bug.cgi?id=700
[2] https://gcc.gnu.org/onlinedocs/gcc-6.4.0/gcc/Warning-Options.html#index-Wunused-const-variable
[3] https://gcc.gnu.org/onlinedocs/gcc-4.9.0/gcc/Warning-Options.html

Cc: Yonghong Zhu <yonghong.zhu@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Liming Gao <liming.gao@intel.com>
[lersek@redhat.com: fix typo in subject]
 		2017-09-08 20:58:54 +02:00
..
XMLSchema BaseTools/Conf/XMLSchema: Reformat XML using Visual Studio 2013 2016-02-19 09:44:32 +08:00
Empty_Package_Information_Data_File.ini Sync BaseTools Branch (version r2271) to EDKII main trunk. 2011-08-26 07:46:26 +00:00
FrameworkDatabase.template
…
ReadMe.txt
…
build_rule.template BaseTools/Gcc ARM AARCH64: add support for building device tree binaries 2017-08-31 08:59:00 +01:00
target.template Sync BaseTool trunk (version r2599) into EDKII BaseTools. 2013-08-23 02:18:16 +00:00
tools_def.template BaseTools/GCC: set -Wno-unused-const-variable on RELEASE builds 2017-09-08 20:58:54 +02:00

ReadMe.txt

This file contains invisible Unicode characters

This file contains invisible Unicode characters that are indistinguishable to humans but may be processed differently by a computer. If you think that this is intentional, you can safely ignore this warning. Use the Escape button to reveal them.

This directory contains the template files for the next generation of the
EDK II Build infrastructure.  These files will be copied into the WORKSPACE's
Conf directory if and only if the target files do not exist.

These files may be updated frequently.

The XMLSchema directory contains the EDK II Packaging XML definitions.  The
schema may change in the future.  It differs somewhat from the early versions
of the XML Schema.