linux-kernel - Re: [PATCH v2 03/19] powerpc: Mark variables as unused

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Message-ID: <20180405090144.Horde.MbhP02FnROsZKa5LclAqgA6@messagerie.si.c-s.fr>
Date:   Thu, 05 Apr 2018 09:01:44 +0200
From:   LEROY Christophe <christophe.leroy@....fr>
To:     Michael Ellerman <mpe@...erman.id.au>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        Mathieu Malaterre <malat@...ian.org>
Subject: Re: [PATCH v2 03/19] powerpc: Mark variables as unused

Michael Ellerman <mpe@...erman.id.au> a écrit :

> LEROY Christophe <christophe.leroy@....fr> writes:
>
>> Mathieu Malaterre <malat@...ian.org> a écrit :
>>
>>> Add gcc attribute unused for two variables. Fix warnings treated as errors
>>> with W=1:
>>>
>>>   arch/powerpc/kernel/prom_init.c:1388:8: error: variable ‘path’ set
>>> but not used [-Werror=unused-but-set-variable]
>>>
>>> Suggested-by: Christophe Leroy <christophe.leroy@....fr>
>>> Signed-off-by: Mathieu Malaterre <malat@...ian.org>
>>> ---
>>> v2: move path within ifdef DEBUG_PROM
>>>
>>>  arch/powerpc/kernel/prom_init.c | 6 +++---
>>>  1 file changed, 3 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/arch/powerpc/kernel/prom_init.c
>>> b/arch/powerpc/kernel/prom_init.c
>>> index acf4b2e0530c..4163b11abb6c 100644
>>> --- a/arch/powerpc/kernel/prom_init.c
>>> +++ b/arch/powerpc/kernel/prom_init.c
>>> @@ -603,7 +603,7 @@ static void __init early_cmdline_parse(void)
>>>  	const char *opt;
>>>
>>>  	char *p;
>>> -	int l = 0;
>>> +	int l __maybe_unused = 0;
>>>
>>>  	prom_cmd_line[0] = 0;
>>>  	p = prom_cmd_line;
>>> @@ -1385,7 +1385,7 @@ static void __init reserve_mem(u64 base, u64 size)
>>>  static void __init prom_init_mem(void)
>>>  {
>>>  	phandle node;
>>> -	char *path, type[64];
>>> +	char *path __maybe_unused, type[64];
>>
>> You should enclose that in an ifdef DEBUG_PROM instead of hiding the warning
>
> I disagree, the result is horrible:
>
>  static void __init prom_init_mem(void)
>  {
> 	phandle node;
> -	char *path, type[64];
> +#ifdef DEBUG_PROM
> +	char *path;
> +#endif
> +	char type[64];
> 	unsigned int plen;
> 	cell_t *p, *endp;
> 	__be32 val;
>
>
> The right fix is to move the debug logic into a helper, and put the path
> in there, eg. something like (not tested):
>
> diff --git a/arch/powerpc/kernel/prom_init.c  
> b/arch/powerpc/kernel/prom_init.c
> index f9d6befb55a6..b02fa2ccc70b 100644
> --- a/arch/powerpc/kernel/prom_init.c
> +++ b/arch/powerpc/kernel/prom_init.c
> @@ -1389,6 +1389,18 @@ static void __init reserve_mem(u64 base, u64 size)
>  	mem_reserve_cnt = cnt + 1;
>  }
>
> +#ifdef DEBUG_PROM
> +static void prom_debug_path(phandle node)
> +{
> +	char *path;
> +	path = prom_scratch;
> +	memset(path, 0, PROM_SCRATCH_SIZE);
> +	call_prom("package-to-path", 3, 1, node, path, PROM_SCRATCH_SIZE-1);
> +	prom_debug("  node %s :\n", path);
> +}
> +#else
> +static void prom_debug_path(phandle node) { }

Or put the ifdef inside the function to avoid double definition ?

> +#endif /* DEBUG_PROM */
>  /*
>   * Initialize memory allocation mechanism, parse "memory" nodes and
>   * obtain that way the top of memory and RMO to setup out local allocator
> @@ -1441,11 +1453,7 @@ static void __init prom_init_mem(void)
>  		p = regbuf;
>  		endp = p + (plen / sizeof(cell_t));
>
> -#ifdef DEBUG_PROM
> -		memset(path, 0, PROM_SCRATCH_SIZE);
> -		call_prom("package-to-path", 3, 1, node, path, PROM_SCRATCH_SIZE-1);
> -		prom_debug("  node %s :\n", path);
> -#endif /* DEBUG_PROM */
> +		prom_debug_path(node);
>
>  		while ((endp - p) >= (rac + rsc)) {
>  			unsigned long base, size;
>
>
> Although that also begs the question of why the hell do we need path at
> all, and not just use prom_scratch directly?

Wondering the same, why not use prom_scratch directly

Christophe

>
> cheers