[LLVMbugs] [Bug 9797] New: False positive: fourth argument can't be null when getaddrinfo() succeeds

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=9797

           Summary: False positive: fourth argument can't be null when
                    getaddrinfo() succeeds
           Product: clang
           Version: 2.9
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Static Analyzer
        AssignedTo: kremenek at apple.com
        ReportedBy: bugs+llvm+org at sebastianhahn.net
                CC: llvmbugs at cs.uiuc.edu


When using getaddrinfo (signature: int getaddrinfo(const char *hostname, const
char *servname, const struct addrinfo *hints, struct addrinfo **res) ), res
can't be null if the call succeeds. The following code triggers a "Loop
condition is false. " message during analysis:

if (!getaddrinfo(name, NULL, &hints, &res))
  for (res_p = res; res_p; res_p = res_p->ai_next) {
    ...
  }

tho clearly, for at least one iteration, the loop must be executed. This
triggers a dereference of null pointer warning further below, when res -
without being modified since the getaddrinfo call - is dereferenced.

I suspect what's going on here is that the analyzer sees the explicit null
check inside the for condition, and decides that the original value might
already have been null. I can work around this warning by adding an assert, but
I suspect the analyzer could be smarter here.

Thanks for your consideration!

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