Re: [v1] powerpc/mpc512x: silence build warning upon disabled DIU
From: Brian Norris <computersforpeace@gmail.com>
Date: 2013-10-09 19:29:39
Hi all, (Please keep me on the CC list, as I'm not subscribed) On Fri, Sep 27, 2013 at 05:28:38PM +0200, Gerhard Sittig wrote:
a disabled Kconfig option results in a reference to a not implemented
routine when the IS_ENABLED() macro is used for both conditional
implementation of the routine as well as a C language source code test
at the call site -- the "if (0) func();" construct only gets eliminated
later by the optimizer, while the compiler already has emitted its
warning about "func()" being undeclared
provide an empty implementation for the mpc512x_setup_diu() and
mpc512x_init_diu() routines in case of the disabled option, to avoid the
compiler warning which is considered fatal and breaks compilation
the bug appeared with commit 2abbbb63c90ab55ca3f054772c2e5ba7df810c48
"powerpc/mpc512x: move common code to shared.c file", how to reproduce:
make mpc512x_defconfig
echo CONFIG_FB_FSL_DIU=n >> .config && make olddefconfig
make
CC arch/powerpc/platforms/512x/mpc512x_shared.o
.../arch/powerpc/platforms/512x/mpc512x_shared.c: In function 'mpc512x_init_early':
.../arch/powerpc/platforms/512x/mpc512x_shared.c:456:3: error: implicit declaration of function 'mpc512x_init_diu' [-Werror=implicit-function-declaration]
.../arch/powerpc/platforms/512x/mpc512x_shared.c: In function 'mpc512x_setup_arch':
.../arch/powerpc/platforms/512x/mpc512x_shared.c:469:3: error: implicit declaration of function 'mpc512x_setup_diu' [-Werror=implicit-function-declaration]
cc1: all warnings being treated as errors
make[4]: *** [arch/powerpc/platforms/512x/mpc512x_shared.o] Error 1I just ran across this same compile issue, and I have a few thoughts below.
quoted hunk ↗ jump to hunk
Signed-off-by: Gerhard Sittig <redacted> CC: <redacted> # v3.11 --- arch/powerpc/platforms/512x/mpc512x_shared.c | 3 +++ 1 file changed, 3 insertions(+)diff --git a/arch/powerpc/platforms/512x/mpc512x_shared.c b/arch/powerpc/platforms/512x/mpc512x_shared.c index a82a41b..1a7b1d0 100644 --- a/arch/powerpc/platforms/512x/mpc512x_shared.c +++ b/arch/powerpc/platforms/512x/mpc512x_shared.c@@ -303,6 +303,9 @@ void __init mpc512x_setup_diu(void) diu_ops.release_bootmem = mpc512x_release_bootmem; } +#else +void __init mpc512x_setup_diu(void) { /* EMPTY */ } +void __init mpc512x_init_diu(void) { /* EMPTY */ } #endif void __init mpc512x_init_IRQ(void)
I see an alternative solution:
Can't almost all of the code in mpc512x_shared.c be declared 'static'?
Then, you can get the real benefit of IS_ENABLED() by removing the
#if IS_ENABLED(CONFIG_FB_FSL_DIU)
from around all the DIU code, and it will automatically be removed by
the compiler when it is not used.
I think the current patch is necessary for immediate use, and it can be
sent to stable. But I might suggest a follow-up patch or 2 that makes
the functions static and kills the #ifdef entirely.
Thanks,
Brian