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]
The majority of the content in the EDK II open source project uses a
BSD 2-Clause License. The EDK II open source project contains
the following components that are covered by additional licenses:
8b6366f875