llvm callgraphscc pass causes core dump - llvm

Question

I wrote an llvm callgraphscc pass, it's very simple as following:
bool MyCallGraphSCCPass::runOnSCC(CallGraphSCC& SCC) {
for (CallGraphSCC::iterator it = SCC.begin(); it != SCC.end(); it++) {
CallGraphNode* node = *it;
Function* func = node->getFunction();
}
return false;
}
This just works fine. However, if I want to print the name of each function as following:
bool MyCallGraphSCCPass::runOnSCC(CallGraphSCC& SCC) {
for (CallGraphSCC::iterator it = SCC.begin(); it != SCC.end(); it++) {
CallGraphNode* node = *it;
Function* func = node->getFunction();
func->getName();
}
return false;
}
Then it can compile (obviously), but when I use opt to run this, there appears an error as following:
0 opt 0x0000000001603412 llvm::sys::PrintStackTrace(_IO_FILE*) + 34
1 opt 0x0000000001602cb4
2 libpthread.so.0 0x00007fd3155f8cb0
3 opt 0x00000000014a86e0 llvm::AttributeSet::getAttributes(unsigned int) const + 0
4 opt 0x00000000014a8748 llvm::AttributeSet::hasAttribute(unsigned int, llvm::Attribute::AttrKind) const + 8
5 call_graph_scc_pass.so 0x00007fd3146062ad test::MyCallGraphSCCPass::runOnSCC(llvm::CallGraphSCC&) + 61
6 opt 0x00000000012aa9aa
7 opt 0x0000000001591188 llvm::legacy::PassManagerImpl::run(llvm::Module&) + 904
8 opt 0x000000000059387b main + 2811
9 libc.so.6 0x00007fd31482976d __libc_start_main + 237
10 opt 0x00000000005b700d
Stack dump:
0. Program arguments: opt -load call_graph_scc_pass.so -scc
1. Running pass 'CallGraph Pass Manager' on module '<stdin>'.
Segmentation fault (core dumped)
Can some one help me with this?

Answer 1

You should check whether the function in the CallGraph is isDeclaration() or not.

Answer 2

This is because node->getFunction() may return a null-pointer and you're not checking for this before dereferencing it.
A CallGraphNode is added to the call graph for all functions in the module without internal linkage. This is because there is a possibility that it could be called from another module. Of course, this is not reachable from the current module, so the caller function is null.
A CallGraphNode is also added if a function address is used for something other than a direct call (such as being stored into memory). It may be called later in a way that the caller can't be tracked statically, so the function field is null here too.