commit 742a85ef574eed16d5d89f454f0eb5a5863ff665
Author: Arnd Bergmann <arnd@arndb.de>
Date:   Sun Sep 10 15:24:40 2017 +0200

    [RFC] Kconfig: disable -Wuninitialized for old compilers

    gcc-4.8 has a lot of false positive warnings with -Wmaybe-uninitialized,
    and we disable those already. However, older compilers have even more
    such false-positive warnings, which clutter the build logs and are not
    disabled because they don't understand the -Wno-maybe-uninitialized
    flag.

    This turns them off as well by disabling -Wuninitialized entirely
    by default (unless 'make W=1' is used), significantly reducing the
    total number of warnings, e.g. on current linux-next:

                            before                          after
                    defconfig       allmodconfig    defconfig       allmodconfig
    gcc-4.3         45              364             0               74
    gcc-4.4         68              210             0               4
    gcc-4.5         33              145             0               6
    gcc-4.6         8               39              0               3
    gcc-4.7         0               12              0               3

    I have also submitted patches for the remaining warnings we get on
    gcc-4.6+, so we should get a clean build at least for allmodconfig with
    this patch. I have also looked at all 39 warnings we get with gcc-4.6 on
    an allmodconfig build. 35 of them are false-positives that newer gccs
    correctly understand and don't warn about. The remaining foud are also
    false-positives, but I would expect gcc to warn about them anyway since
    it cannot see why the code is safe:

    drivers/media/platform/rcar_drif.c:658:2: error: ‘ret’ may be used uninitialized in this function [-Werror=uninitialized]
    drivers/mtd/spi-nor/stm32-quadspi.c:248:2: error: ‘ret’ may be used uninitialized in this function [-Werror=uninitialized]
    drivers/net/ethernet/mellanox/mlx5/core/fpga/sdk.c:147:6: error: ‘err’ may be used uninitialized in this function [-Werror=uninitialized]
    drivers/net/ethernet/mellanox/mlx5/core/fpga/sdk.c:126:6: error: ‘err’ may be used uninitialized in this function [-Werror=uninitialized]

    All four cases are for code that initializes a return code in a loop
    that may be entered at all for invalid arguments (typically a counter).

    Newer gcc and clang transform this so the return code of the function
    becomes zero unless one loop iteration has failed earlier. The variable
    holding the return code is optimized away before those warnings get
    generated. In practice, those functions should never be called with a
    zero loop counter, but I decided to submit patches for them anyway.
    Presumably, smatch also detects all four as uninitialized variable uses,
    but I did not try that.

    Cc: Geert Uytterhoeven <geert@linux-m68k.org>
    Cc: Dan Carpenter <dan.carpenter@oracle.com>
    Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82203
    Signed-off-by: Arnd Bergmann <arnd@arndb.de>
    ---
    Geert, you probably have an opinion on this, as you do build-testing
    with gcc-4.1 and regularly report new warnings you get. I think
    overall, we are better off without the false-positives here, and
    we still get the regular warnings from newer compilers.

    Would this patch get in your way?

diff --git a/Makefile b/Makefile
index 467042f98be5..d1c7933fab76 100644
--- a/Makefile
+++ b/Makefile
@@ -633,7 +633,10 @@ KBUILD_CFLAGS   += -O2
 endif
 endif

-KBUILD_CFLAGS += $(call cc-ifversion, -lt, 0409, \
+KBUILD_CFLAGS += $(call cc-ifversion, -lt, 0408, \
+                       $(call cc-disable-warning,uninitialized,))
+
+KBUILD_CFLAGS += $(call cc-ifversion, -eq, 0408, \
                        $(call cc-disable-warning,maybe-uninitialized,))

 # Tell gcc to never replace conditional load with a non-conditional one
diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
index 4fac8fe024b7..7b9003515fa6 100644
--- a/scripts/Makefile.extrawarn
+++ b/scripts/Makefile.extrawarn
@@ -28,6 +28,7 @@ warning-1 += $(call cc-option, -Wunused-but-set-variable)
 warning-1 += $(call cc-option, -Wunused-const-variable)
 warning-1 += $(call cc-disable-warning, missing-field-initializers)
 warning-1 += $(call cc-disable-warning, sign-compare)
+warning-1 += -Wuninitialized

 warning-2 := -Waggregate-return
 warning-2 += -Wcast-align