[PATCH] tap: Avoid bogus missingReturn cppcheck warning in tap_l2_max_len()

[PATCH] tap: Avoid bogus missingReturn cppcheck warning in tap_l2_max_len()

[Stefano Brivio]

Cppcheck 2.14.2 on Alpine Linux (musl) says that:

tap.c:111:19: error: Found an exit path from function with non-void return type that has missing return statement [missingReturn]
 switch (c->mode) {
                  ^

This exit path is not reachable because we ASSERT(0) after the switch,
but for some reason cppcheck doesn't see this with musl headers. Hide
the warning with a redundant return statement.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
---
 tap.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/tap.c b/tap.c
index d630f6d..6db5d88 100644
--- a/tap.c
+++ b/tap.c
@@ -118,6 +118,8 @@ unsigned long tap_l2_max_len(const struct ctx *c)
 	}
 	/* NOLINTEND(bugprone-branch-clone) */
 	ASSERT(0);
+
+	return 0; /* Unreachable, for cppcheck's sake */
 }
 
 /**
-- 
@@ -118,6 +118,8 @@ unsigned long tap_l2_max_len(const struct ctx *c)
 	}
 	/* NOLINTEND(bugprone-branch-clone) */
 	ASSERT(0);
+
+	return 0; /* Unreachable, for cppcheck's sake */
 }
 
 /**
-- 
2.43.0

Re: [PATCH] tap: Avoid bogus missingReturn cppcheck warning in tap_l2_max_len()

[David Gibson]

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On Thu, May 15, 2025 at 06:05:01PM +0200, Stefano Brivio wrote:
> Cppcheck 2.14.2 on Alpine Linux (musl) says that:
> 
> tap.c:111:19: error: Found an exit path from function with non-void return type that has missing return statement [missingReturn]
>  switch (c->mode) {
>                   ^
> 
> This exit path is not reachable because we ASSERT(0) after the switch,
> but for some reason cppcheck doesn't see this with musl headers. Hide
> the warning with a redundant return statement.
> 
> Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

Hm.  Alternatively you could change this to call abort_with_msg()
directly.  That's marked as ((noreturn)) so with any luck cppcheck
will then be able to figure out what's going on.  Although, I'm
slightly surprised it can't do so already: I thought I put the
((noreturn)) in there to avoid warnings exactly like this.

> ---
>  tap.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/tap.c b/tap.c
> index d630f6d..6db5d88 100644
> --- a/tap.c
> +++ b/tap.c
> @@ -118,6 +118,8 @@ unsigned long tap_l2_max_len(const struct ctx *c)
>  	}
>  	/* NOLINTEND(bugprone-branch-clone) */
>  	ASSERT(0);
> +
> +	return 0; /* Unreachable, for cppcheck's sake */
>  }
>  
>  /**

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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Re: [PATCH] tap: Avoid bogus missingReturn cppcheck warning in tap_l2_max_len()

[Stefano Brivio]

On Fri, 16 May 2025 17:25:21 +1000
David Gibson <david@gibson.dropbear.id.au> wrote:

> On Thu, May 15, 2025 at 06:05:01PM +0200, Stefano Brivio wrote:
> > Cppcheck 2.14.2 on Alpine Linux (musl) says that:
> > 
> > tap.c:111:19: error: Found an exit path from function with non-void return type that has missing return statement [missingReturn]
> >  switch (c->mode) {
> >                   ^
> > 
> > This exit path is not reachable because we ASSERT(0) after the switch,
> > but for some reason cppcheck doesn't see this with musl headers. Hide
> > the warning with a redundant return statement.
> > 
> > Signed-off-by: Stefano Brivio <sbrivio@redhat.com>  
> 
> Hm.  Alternatively you could change this to call abort_with_msg()
> directly.  That's marked as ((noreturn)) so with any luck cppcheck
> will then be able to figure out what's going on.  Although, I'm
> slightly surprised it can't do so already: I thought I put the
> ((noreturn)) in there to avoid warnings exactly like this.

So, I checked, and abort_with_msg(""); works. ASSERT() ultimately
expands to abort_with_msg(), but for some reason cppcheck together with
Clang can't "follow" that, I suppose it's something related to the
pre-processor.

But in any case, abort_with_msg("") doesn't look as descriptive and
as obviously redundant as a return statement with a comment, so I don't
quite see the benefit changing it (also considering that I need to test
other versions, which takes time).

-- 
Stefano

Re: [PATCH] tap: Avoid bogus missingReturn cppcheck warning in tap_l2_max_len()

[David Gibson]

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On Fri, May 16, 2025 at 06:26:23PM +0200, Stefano Brivio wrote:
> On Fri, 16 May 2025 17:25:21 +1000
> David Gibson <david@gibson.dropbear.id.au> wrote:
> 
> > On Thu, May 15, 2025 at 06:05:01PM +0200, Stefano Brivio wrote:
> > > Cppcheck 2.14.2 on Alpine Linux (musl) says that:
> > > 
> > > tap.c:111:19: error: Found an exit path from function with non-void return type that has missing return statement [missingReturn]
> > >  switch (c->mode) {
> > >                   ^
> > > 
> > > This exit path is not reachable because we ASSERT(0) after the switch,
> > > but for some reason cppcheck doesn't see this with musl headers. Hide
> > > the warning with a redundant return statement.
> > > 
> > > Signed-off-by: Stefano Brivio <sbrivio@redhat.com>  
> > 
> > Hm.  Alternatively you could change this to call abort_with_msg()
> > directly.  That's marked as ((noreturn)) so with any luck cppcheck
> > will then be able to figure out what's going on.  Although, I'm
> > slightly surprised it can't do so already: I thought I put the
> > ((noreturn)) in there to avoid warnings exactly like this.
> 
> So, I checked, and abort_with_msg(""); works. ASSERT() ultimately
> expands to abort_with_msg(), but for some reason cppcheck together with
> Clang can't "follow" that, I suppose it's something related to the
> pre-processor.
> 
> But in any case, abort_with_msg("") doesn't look as descriptive and
> as obviously redundant as a return statement with a comment, so I don't
> quite see the benefit changing it (also considering that I need to test
> other versions, which takes time).

Well, kind of the whole point of abort_with_msg() is that you can give
it a meaningful message, which might change the picture.  It would
also be trivial to write an unreachable() wrapper around that.

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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Re: [PATCH] tap: Avoid bogus missingReturn cppcheck warning in tap_l2_max_len()

[Stefano Brivio]

On Sat, 17 May 2025 20:29:20 +1000
David Gibson <david@gibson.dropbear.id.au> wrote:

> On Fri, May 16, 2025 at 06:26:23PM +0200, Stefano Brivio wrote:
> > On Fri, 16 May 2025 17:25:21 +1000
> > David Gibson <david@gibson.dropbear.id.au> wrote:
> >   
> > > On Thu, May 15, 2025 at 06:05:01PM +0200, Stefano Brivio wrote:  
> > > > Cppcheck 2.14.2 on Alpine Linux (musl) says that:
> > > > 
> > > > tap.c:111:19: error: Found an exit path from function with non-void return type that has missing return statement [missingReturn]
> > > >  switch (c->mode) {
> > > >                   ^
> > > > 
> > > > This exit path is not reachable because we ASSERT(0) after the switch,
> > > > but for some reason cppcheck doesn't see this with musl headers. Hide
> > > > the warning with a redundant return statement.
> > > > 
> > > > Signed-off-by: Stefano Brivio <sbrivio@redhat.com>    
> > > 
> > > Hm.  Alternatively you could change this to call abort_with_msg()
> > > directly.  That's marked as ((noreturn)) so with any luck cppcheck
> > > will then be able to figure out what's going on.  Although, I'm
> > > slightly surprised it can't do so already: I thought I put the
> > > ((noreturn)) in there to avoid warnings exactly like this.  
> > 
> > So, I checked, and abort_with_msg(""); works. ASSERT() ultimately
> > expands to abort_with_msg(), but for some reason cppcheck together with
> > Clang can't "follow" that, I suppose it's something related to the
> > pre-processor.
> > 
> > But in any case, abort_with_msg("") doesn't look as descriptive and
> > as obviously redundant as a return statement with a comment, so I don't
> > quite see the benefit changing it (also considering that I need to test
> > other versions, which takes time).  
> 
> Well, kind of the whole point of abort_with_msg() is that you can give
> it a meaningful message, which might change the picture.

Right, but I was struggling with making it meaningful: "dodged cppcheck
warning, you'll never see this"? I much prefer a return with a comment.

> It would
> also be trivial to write an unreachable() wrapper around that.

Ah, that would be nice, yes. I would consider writing one after 2-3
more cases like this.

-- 
Stefano