[PATCH] ftrace: sample: avoid open-coded 64-bit division

[PATCH] ftrace: sample: avoid open-coded 64-bit division

[Arnd Bergmann]

From: Arnd Bergmann <arnd@arndb.de>

Calculating the average period requires a 64-bit division that leads
to a link failure on 32-bit architectures:

x86_64-linux-ld: samples/ftrace/ftrace-ops.o: in function `ftrace_ops_sample_init':
ftrace-ops.c:(.init.text+0x23b): undefined reference to `__udivdi3'

Use the div_u64() helper to do this instead. Since this is an init function that
is not called frequently, the runtime overhead is going to be acceptable.

Fixes: b56c68f705ca ("ftrace: Add sample with custom ops")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 samples/ftrace/ftrace-ops.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/samples/ftrace/ftrace-ops.c b/samples/ftrace/ftrace-ops.c
index 24deb51c7261..0c8da87ff5c3 100644
--- a/samples/ftrace/ftrace-ops.c
+++ b/samples/ftrace/ftrace-ops.c
@@ -223,7 +223,7 @@ static int __init ftrace_ops_sample_init(void)
 
 	pr_info("Attempted %u calls to %ps in %lluns (%lluns / call)\n",
 		nr_function_calls, tracee_relevant,
-		period, period / nr_function_calls);
+		period, div_u64(period, nr_function_calls));
 
 	if (persist)
 		return 0;
-- 
2.39.0

Re: [PATCH] ftrace: sample: avoid open-coded 64-bit division

[Mark Rutland]

On Mon, Jan 30, 2023 at 02:02:37PM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
> 
> Calculating the average period requires a 64-bit division that leads
> to a link failure on 32-bit architectures:
> 
> x86_64-linux-ld: samples/ftrace/ftrace-ops.o: in function `ftrace_ops_sample_init':
> ftrace-ops.c:(.init.text+0x23b): undefined reference to `__udivdi3'

Whoops; sorry about that.

> Use the div_u64() helper to do this instead. Since this is an init function that
> is not called frequently, the runtime overhead is going to be acceptable.
> 
> Fixes: b56c68f705ca ("ftrace: Add sample with custom ops")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Acked-by: Mark Rutland <mark.rutland@arm.com>

Mark.

> ---
>  samples/ftrace/ftrace-ops.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/samples/ftrace/ftrace-ops.c b/samples/ftrace/ftrace-ops.c
> index 24deb51c7261..0c8da87ff5c3 100644
> --- a/samples/ftrace/ftrace-ops.c
> +++ b/samples/ftrace/ftrace-ops.c
> @@ -223,7 +223,7 @@ static int __init ftrace_ops_sample_init(void)
>  
>  	pr_info("Attempted %u calls to %ps in %lluns (%lluns / call)\n",
>  		nr_function_calls, tracee_relevant,
> -		period, period / nr_function_calls);
> +		period, div_u64(period, nr_function_calls));
>  
>  	if (persist)
>  		return 0;
> -- 
> 2.39.0
>