[PATCH] powerpc/dt_cpu_ftrs: Avoid separate strlen() in scan_callback()

[PATCH] powerpc/dt_cpu_ftrs: Avoid separate strlen() in scan_callback()

[Thorsten Blum]

Use the return value of strscpy() when copying the display name instead
of checking the source string length with strlen() first.

Keep dt_cpu_name static but move it into dt_cpu_ftrs_scan_callback(),
where it is assigned.

Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
---
 arch/powerpc/kernel/dt_cpu_ftrs.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/kernel/dt_cpu_ftrs.c b/arch/powerpc/kernel/dt_cpu_ftrs.c
index 3af6c06af02f..8d8e94e4d2bc 100644
--- a/arch/powerpc/kernel/dt_cpu_ftrs.c
+++ b/arch/powerpc/kernel/dt_cpu_ftrs.c
@@ -90,8 +90,6 @@ static void __restore_cpu_cpufeatures(void)
 		init_pmu_registers();
 }
 
-static char dt_cpu_name[64];
-
 static struct cpu_spec __initdata base_cpu_spec = {
 	.cpu_name		= NULL,
 	.cpu_features		= CPU_FTRS_DT_CPU_BASE,
@@ -1069,6 +1067,7 @@ static int __init count_cpufeatures_subnodes(unsigned long node,
 static int __init dt_cpu_ftrs_scan_callback(unsigned long node, const char
 					    *uname, int depth, void *data)
 {
+	static char dt_cpu_name[64];
 	const __be32 *prop;
 	int count, i;
 	u32 isa;
@@ -1106,10 +1105,8 @@ static int __init dt_cpu_ftrs_scan_callback(unsigned long node, const char
 	}
 
 	prop = of_get_flat_dt_prop(node, "display-name", NULL);
-	if (prop && strlen((char *)prop) != 0) {
-		strscpy(dt_cpu_name, (char *)prop, sizeof(dt_cpu_name));
+	if (prop && strscpy(dt_cpu_name, (char *)prop) != 0)
 		cur_cpu_spec->cpu_name = dt_cpu_name;
-	}
 
 	cpufeatures_setup_finished();
 

Re: [PATCH] powerpc/dt_cpu_ftrs: Avoid separate strlen() in scan_callback()

[David Laight]

On Tue, 30 Jun 2026 17:46:56 +0200
Thorsten Blum <thorsten.blum@linux.dev> wrote:

> Use the return value of strscpy() when copying the display name instead
> of checking the source string length with strlen() first.
> 
> Keep dt_cpu_name static but move it into dt_cpu_ftrs_scan_callback(),
> where it is assigned.
> 
> Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
> ---
>  arch/powerpc/kernel/dt_cpu_ftrs.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/dt_cpu_ftrs.c b/arch/powerpc/kernel/dt_cpu_ftrs.c
> index 3af6c06af02f..8d8e94e4d2bc 100644
> --- a/arch/powerpc/kernel/dt_cpu_ftrs.c
> +++ b/arch/powerpc/kernel/dt_cpu_ftrs.c
> @@ -90,8 +90,6 @@ static void __restore_cpu_cpufeatures(void)
>  		init_pmu_registers();
>  }
>  
> -static char dt_cpu_name[64];
> -
>  static struct cpu_spec __initdata base_cpu_spec = {
>  	.cpu_name		= NULL,
>  	.cpu_features		= CPU_FTRS_DT_CPU_BASE,
> @@ -1069,6 +1067,7 @@ static int __init count_cpufeatures_subnodes(unsigned long node,
>  static int __init dt_cpu_ftrs_scan_callback(unsigned long node, const char
>  					    *uname, int depth, void *data)
>  {
> +	static char dt_cpu_name[64];
>  	const __be32 *prop;
>  	int count, i;
>  	u32 isa;
> @@ -1106,10 +1105,8 @@ static int __init dt_cpu_ftrs_scan_callback(unsigned long node, const char
>  	}
>  
>  	prop = of_get_flat_dt_prop(node, "display-name", NULL);
> -	if (prop && strlen((char *)prop) != 0) {
> -		strscpy(dt_cpu_name, (char *)prop, sizeof(dt_cpu_name));
> +	if (prop && strscpy(dt_cpu_name, (char *)prop) != 0)

That is different code.
The old code only did the copy if the new string was non-empty.
So you want to replace the strlen() with *(char *)prop != 0.
Checks for strlen() == 0 are silly (but surprisingly common).
A search might show up this gem:
	str[strlen(str)] = 0;

-- David


>  		cur_cpu_spec->cpu_name = dt_cpu_name;
> -	}
>  
>  	cpufeatures_setup_finished();
>  
> 

Re: [PATCH] powerpc/dt_cpu_ftrs: Avoid separate strlen() in scan_callback()

[Thorsten Blum]

On Tue, Jun 30, 2026 at 06:38:10PM +0100, David Laight wrote:
> On Tue, 30 Jun 2026 17:46:56 +0200
> Thorsten Blum <thorsten.blum@linux.dev> wrote:
> 
> > Use the return value of strscpy() when copying the display name instead
> > of checking the source string length with strlen() first.
> > 
> > Keep dt_cpu_name static but move it into dt_cpu_ftrs_scan_callback(),
> > where it is assigned.
> > 
> > Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
> > ---
> >  arch/powerpc/kernel/dt_cpu_ftrs.c | 7 ++-----
> >  1 file changed, 2 insertions(+), 5 deletions(-)
> > 
> > diff --git a/arch/powerpc/kernel/dt_cpu_ftrs.c b/arch/powerpc/kernel/dt_cpu_ftrs.c
> > index 3af6c06af02f..8d8e94e4d2bc 100644
> > --- a/arch/powerpc/kernel/dt_cpu_ftrs.c
> > +++ b/arch/powerpc/kernel/dt_cpu_ftrs.c
> > @@ -90,8 +90,6 @@ static void __restore_cpu_cpufeatures(void)
> >  		init_pmu_registers();
> >  }
> >  
> > -static char dt_cpu_name[64];
> > -
> >  static struct cpu_spec __initdata base_cpu_spec = {
> >  	.cpu_name		= NULL,
> >  	.cpu_features		= CPU_FTRS_DT_CPU_BASE,
> > @@ -1069,6 +1067,7 @@ static int __init count_cpufeatures_subnodes(unsigned long node,
> >  static int __init dt_cpu_ftrs_scan_callback(unsigned long node, const char
> >  					    *uname, int depth, void *data)
> >  {
> > +	static char dt_cpu_name[64];
> >  	const __be32 *prop;
> >  	int count, i;
> >  	u32 isa;
> > @@ -1106,10 +1105,8 @@ static int __init dt_cpu_ftrs_scan_callback(unsigned long node, const char
> >  	}
> >  
> >  	prop = of_get_flat_dt_prop(node, "display-name", NULL);
> > -	if (prop && strlen((char *)prop) != 0) {
> > -		strscpy(dt_cpu_name, (char *)prop, sizeof(dt_cpu_name));
> > +	if (prop && strscpy(dt_cpu_name, (char *)prop) != 0)
> 
> That is different code.
> The old code only did the copy if the new string was non-empty.

Good catch, thanks!

I just sent a v2:
https://lore.kernel.org/lkml/20260701114428.818748-3-thorsten.blum@linux.dev/