linux-kernel - Re: [PATCH 01/21] powerpc: Remove warning on array size when empty

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Date:   Thu, 01 Mar 2018 13:55:57 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Mathieu Malaterre <malat@...ian.org>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Jiri Slaby <jslaby@...e.com>, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, Mathieu Malaterre <malat@...ian.org>
Subject: Re: [PATCH 01/21] powerpc: Remove warning on array size when empty

Mathieu Malaterre <malat@...ian.org> writes:

> When neither CONFIG_ALTIVEC, nor CONFIG_VSX or CONFIG_PPC64 is defined, the
> array feature_properties is defined as an empty array, which in turn
> triggers the following warning (treated as error on W=1):
>
>   CC      arch/powerpc/kernel/prom.o
> arch/powerpc/kernel/prom.c: In function ‘check_cpu_feature_properties’:
> arch/powerpc/kernel/prom.c:298:16: error: comparison of unsigned expression < 0 is always false [-Werror=type-limits]
>   for (i = 0; i < ARRAY_SIZE(feature_properties); ++i, ++fp) {
>                 ^
> cc1: all warnings being treated as errors

Ugh, that's annoying.

This seems to work?

diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
index 4dffef947b8a..5215119e249c 100644
--- a/arch/powerpc/kernel/prom.c
+++ b/arch/powerpc/kernel/prom.c
@@ -291,11 +291,11 @@ static inline void identical_pvr_fixup(unsigned long node)
 
 static void __init check_cpu_feature_properties(unsigned long node)
 {
-	unsigned long i;
 	struct feature_property *fp = feature_properties;
 	const __be32 *prop;
+	int i;
 
-	for (i = 0; i < ARRAY_SIZE(feature_properties); ++i, ++fp) {
+	for (i = 0; i < (int)ARRAY_SIZE(feature_properties); ++i, ++fp) {
 		prop = of_get_flat_dt_prop(node, fp->name, NULL);
 		if (prop && be32_to_cpup(prop) >= fp->min_value) {
 			cur_cpu_spec->cpu_features |= fp->cpu_feature;


cheers