false positives after rte_panic

[Paul Aitken]

cppcheck doesn't understand that rte_panic terminates execution, so given code like below, "cppcheck --enable=warning" warns:

"Either the condition '!ptr' is redundant or there is possible null pointer dereference: ptr."

This is not reported if a "return" is added under the rte_panic.

    ptr = fn();
    if (!ptr) {
        rte_panic("couldn't get ptr");
    }

    dostuff(ptr->member, foo, bar);

[Daniel Marjamäki]

you can fix that with a configuration file. a start (untested):

<?xml version="1.0"?>
<def format="2">
  <function name="rte_panic">
      <noreturn/>
       <arg nr="1">
           <not-uninit/>
       </arg>
    </function>
</def>

[Paul Aitken]

Thanks Daniel.

• <noreturn/> segfaulted.
• <noreturn>true</noreturn> is parsed, but produces the same output as before: "Either the condition is redundant or there is possible null pointer dereference".
• <noreturn>false</noreturn> also produces the same output (as expected).

"--check-library" shows that it's definitely picking up the rte_panic def from the config file.

(Using cppcheck @ a7707a457)

[Paul Aitken]

Any more thoughts on this, @danielmarjamaki ?

[Daniel Marjamäki]

could you give an example code that reproduce the problem

danielm@debian:~/cppcheck$ ./cppcheck --enable=style 1.c
Checking 1.c ...
1.c:2:5: error: syntax error: keyword 'if' is not allowed in global scope [syntaxError]
    if (!ptr) {
    ^
danielm@debian:~/cppcheck$ cat 1.c
    ptr = fn();
    if (!ptr) {
        rte_panic("couldn't get ptr");
    }

    dostuff(ptr->member, foo, bar);

[Daniel Marjamäki]

.. and when I try to fill in some code I don't get the false positive.

[Paul Aitken]

@danielmarjamaki, use "cppcheck --enable=warning".

For example:

void example(void)
{
    struct passwd *pw = getpwuid(dataplane_uid);

    if (!pw)
        rte_panic("could not getpwuid: %s\n", strerror(errno));

    getgrouplist(pw->pw_name, dataplane_gid, NULL, &ngroups);
}

$ cppcheck --enable=warning 1.c
Checking 1.c ...
1.c:8:15: warning: Either the condition '!pw' is redundant or there is possible null pointer dereference: pw. [nullPointerRedundantCheck]
 getgrouplist(pw->pw_name, dataplane_gid, NULL, &ngroups);
              ^
1.c:5:9: note: Assuming that condition '!pw' is not redundant
    if (!pw) {
        ^
1.c:8:15: note: Null pointer dereference
 getgrouplist(pw->pw_name, dataplane_gid, NULL, &ngroups);
              ^

Since rte_panic doesn't return, a null pointer can never be dereferenced.

[Paul Aitken]

This works:

   <function name="rte_panic">
     <noreturn>true</noreturn>
     <arg nr="variadic"/>
   </function>

<arg nr="all"/> doesn't work.
<noreturn/> segfaults.

[Daniel Marjamäki]

it looks like rte_panic takes a format string..

<?xml version="1.0"?>
<def format="2">
  <function name="rte_panic">
      <noreturn>true</noreturn>
      <formatstr/>
      <arg nr="1" direction="in">
          <not-uninit/>
          <formatstr/>
      </arg>
    </function>
</def>

That solves the false positive for me.

[Paul Aitken]

That's even better, thanks @danielmarjamaki.

Would you add that to one of the existing cfg files, or start a new one for DPDK APIs?

[Daniel Marjamäki]

I would probably create a new dpdk.cfg file.. if you create that and share it with me I will add it in Cppcheck.

[Paul Aitken]

Thanks @danielmarjamaki.

See https://github.com/danmar/cppcheck/pull/3313