2024-01-05 17:40:27

by Breno Leitao

Subject: [PATCH net-next] net/ipv6: resolve warning in ip6_fib.c

In some configurations, the 'iter' variable in function
fib6_repair_tree() is unused, resulting the following warning when
compiled with W=1.

net/ipv6/ip6_fib.c:1781:6: warning: variable 'iter' set but not used [-Wunused-but-set-variable]
1781 | int iter = 0;
| ^

Rewrite RT6_TRACE() macro to keep the variable in scope.

Clang 18 removes the trace completely from the binary when the trace is
disabled[1], so, no overhead is expected with this change.

[1] Link: https://paste.debian.net/1303162/

Signed-off-by: Breno Leitao <[email protected]>
---
include/net/ip6_fib.h | 6 +-----
1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/include/net/ip6_fib.h b/include/net/ip6_fib.h
index 9ba6413fd2e3..d2ef60ebeb25 100644
--- a/include/net/ip6_fib.h
+++ b/include/net/ip6_fib.h
@@ -30,11 +30,7 @@

#define RT6_DEBUG 2

-#if RT6_DEBUG >= 3
-#define RT6_TRACE(x...) pr_debug(x)
-#else
-#define RT6_TRACE(x...) do { ; } while (0)
-#endif
+#define RT6_TRACE(x...) do { if (RT6_DEBUG > 3) pr_debug(x); } while (0)

struct rt6_info;
struct fib6_info;
--
2.39.3

2024-01-06 16:14:05

by David Ahern

Subject: Re: [PATCH net-next] net/ipv6: resolve warning in ip6_fib.c

On 1/5/24 10:39 AM, Breno Leitao wrote:
> In some configurations, the 'iter' variable in function
> fib6_repair_tree() is unused, resulting the following warning when
> compiled with W=1.
>
> net/ipv6/ip6_fib.c:1781:6: warning: variable 'iter' set but not used [-Wunused-but-set-variable]
> 1781 | int iter = 0;
> | ^
>
> Rewrite RT6_TRACE() macro to keep the variable in scope.
>
> Clang 18 removes the trace completely from the binary when the trace is
> disabled[1], so, no overhead is expected with this change.
>
> [1] Link: https://paste.debian.net/1303162/
>
> Signed-off-by: Breno Leitao <[email protected]>
> ---
> include/net/ip6_fib.h | 6 +-----
> 1 file changed, 1 insertion(+), 5 deletions(-)
>
> diff --git a/include/net/ip6_fib.h b/include/net/ip6_fib.h
> index 9ba6413fd2e3..d2ef60ebeb25 100644
> --- a/include/net/ip6_fib.h
> +++ b/include/net/ip6_fib.h
> @@ -30,11 +30,7 @@
>
> #define RT6_DEBUG 2
>
> -#if RT6_DEBUG >= 3
> -#define RT6_TRACE(x...) pr_debug(x)
> -#else
> -#define RT6_TRACE(x...) do { ; } while (0)
> -#endif
> +#define RT6_TRACE(x...) do { if (RT6_DEBUG > 3) pr_debug(x); } while (0)
>
> struct rt6_info;
> struct fib6_info;

I question the value of RT6_TRACE vs just using pr_debug; pr_debug has
zero cost until enabled and can be enabled by file or line. Not
requiring a kernel build is actual better.

[cc'ed Wei who added the macro]

2024-01-08 15:18:07

by Breno Leitao

Subject: Re: [PATCH net-next] net/ipv6: resolve warning in ip6_fib.c

On Sat, Jan 06, 2024 at 09:13:53AM -0700, David Ahern wrote:
> On 1/5/24 10:39 AM, Breno Leitao wrote:

> > -#if RT6_DEBUG >= 3
> > -#define RT6_TRACE(x...) pr_debug(x)
> > -#else
> > -#define RT6_TRACE(x...) do { ; } while (0)
> > -#endif
> > +#define RT6_TRACE(x...) do { if (RT6_DEBUG > 3) pr_debug(x); } while (0)
> >
> > struct rt6_info;
> > struct fib6_info;
>
> I question the value of RT6_TRACE vs just using pr_debug; pr_debug has
> zero cost until enabled and can be enabled by file or line. Not
> requiring a kernel build is actual better.
>
> [cc'ed Wei who added the macro]

I also questioned it.

Anyway, if we don't hear any strong opinion in favor of RT6_TRACE(), I
will replace it by pr_debug() in a v2.