test: fix printf formating

[alfredh]

extracted from this patch:

#758

[alfredh]

hi @maximilianfridrich

Could you please run your LLVM vararg tool after this, and see if it can find any issues ?

[maximilianfridrich]

It did not find an issue. The tool is quite simple: It checks if the last non-variable argument to a variadic function is a non-constant string. If that is the case, it prints a warning.

So some of these warning are actually okay to ignore, but the origin of such a non-constant argument needs to be carefully checked by hand if it can be (partially) controlled by an external user. E.g. that was the case in the multipart sdp decoding function, because the boundary string is controlled externally and was then passed to the re_regex function.

Here is the core of the LLVM function pass:

void visitor(Function &F) {
  for (auto &BB : F) {
    for (auto &Ins : BB) {

      auto *CB = dyn_cast<CallBase>(&Ins);
      if (nullptr == CB) {
        continue;
      }
      // If CB is a direct function call then DirectInvoc will be not null.
      auto *DirectInvoc = CB->getCalledFunction();
      if (nullptr == DirectInvoc) {
        continue;
      }
      if (DirectInvoc->isVarArg()) {
        int LastIndex = DirectInvoc->arg_size() - 1;
        Value *LastArg = CB->getArgOperand(LastIndex);

        if (!isa<Constant>(LastArg) && !isa<ConstantDataSequential>(LastArg)) {
          errs()
              << "Warning: In function " << F.getName() << " calling function "
              << DirectInvoc->getName()
              << " where the last non-variable argument is not a constant "
                 "string\n";
        }
      }
    }
  }
}