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

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Stefano Brivio

15 May 2025 15 May '25

6:05 p.m.

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 --- 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 */ } /** -- 2.43.0

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David Gibson

16 May 16 May

9:25 a.m.

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

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

Stefano Brivio

6:26 p.m.

On Fri, 16 May 2025 17:25:21 +1000 David Gibson 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

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

David Gibson

17 May 17 May

12:29 p.m.

On Fri, May 16, 2025 at 06:26:23PM +0200, Stefano Brivio wrote:

...

On Fri, 16 May 2025 17:25:21 +1000 David Gibson 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

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

Stefano Brivio

19 May 19 May

9:27 a.m.

On Sat, 17 May 2025 20:29:20 +1000 David Gibson 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 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

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

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