[llvm-dev] Why getFunction() of CallGraphNode return NULL function?

[Qiuping Yi via llvm-dev]

So, I won't know the called function statically, Right?


--------------------------------------------
Qiuping Yi
Institute Of Software
Chinese Academy of Sciences

On Wed, Jan 20, 2016 at 2:24 PM, Nema, Ashutosh <Ashutosh.Nema at amd.com>
wrote:

> Typically for C++ virtual function you will see an indirect callSite
> (unless not de-virtualized).
>
>
>
> Regards,
>
> Ashutosh
>
>
>
> *From:* Qiuping Yi [mailto:yiqiuping at gmail.com]
> *Sent:* Wednesday, January 20, 2016 9:10 AM
> *To:* Nema, Ashutosh
> *Cc:* llvm-dev
> *Subject:* Re: [llvm-dev] Why getFunction() of CallGraphNode return NULL
> function?
>
>
>
> Dear Ashutosh,
>
>
>
> Thank you, I can handle some indirect callSites by getFunction() of
> InvokInst and CallInst.
>
>
>
> However, when I am handling C++ programs, I found the calls of member
> functions are converted
>
> to some strange  indirect calls. For example:
>
>
>
> table->truncate(sysTransaction);   // from mysql
>
>
>
> are translated to the next complex llvm IR:
>
>
>
> _ZN8Database20getSystemTransactionEv.exit:        ; preds = %bb33
>
>   call void @llvm.dbg.value(metadata %class.Transaction.553* %tmp36, i64
> 0, metadata !7310, metadata !53545), !dbg !69981
>
>   %tmp37 = bitcast %class.Table.543* %table to void (%class.Table.543*,
> %class.Transaction.553*)***, !dbg !69982
>
>   %tmp38 = load void (%class.Table.543*, %class.Transaction.553*)***
> %tmp37, align 8, !dbg !69982, !tbaa !53550
>
>   %tmp39 = getelementptr inbounds void (%class.Table.543*,
> %class.Transaction.553*)** %tmp38, i64 5, !dbg !69982
>
>   %tmp40 = load void (%class.Table.543*, %class.Transaction.553*)**
> %tmp39, align 8, !dbg !69982
>
>   invoke void %tmp40(%class.Table.543* %table, %class.Transaction.553*
> %tmp36)
>
>           to label %bb41 unwind label %bb72, !dbg !69982
>
>
>
> and thus I cannot find the called function "truncate" from "invoke void
> %tmp40(...)", what should I do?
>
> I didn't analysis C++ code with llvm, does all the function calls through
> objects are translated to such complex indirect calls?
>
> If so, how can I dereference such functions? Thanks!
>
>
>
>
>
> --------------------------------------------
> Qiuping Yi
> Institute Of Software
> Chinese Academy of Sciences
>
>
>
> On Tue, Jan 19, 2016 at 8:23 PM, Nema, Ashutosh <Ashutosh.Nema at amd.com>
> wrote:
>
> You will see NULL for indirect callSite.
>
> May need to add additional checks for this possibility.
>
>
>
> Regards,
>
> Ashutosh
>
>
>
> *From:* llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] *On Behalf Of *Qiuping
> Yi via llvm-dev
> *Sent:* Tuesday, January 19, 2016 5:35 PM
> *To:* llvm-dev at lists.llvm.org
> *Subject:* [llvm-dev] Why getFunction() of CallGraphNode return NULL
> function?
>
>
>
> Hi all,
>
>
>
> I want to find all the called functions in each function, thus I iterate
> the calledFunctions of each CallGraphNode in CallGraph as follow:
>
>
>
> for (CallGraph::iterator it = CG->begin(); it != CG->end(); ++it) {
>
>    CallGraphNode* node = it->second;
>
>    for (CallGraphNode::iterator it2 = node->begin(); it2 != node->end();
> ++it2) {
>
>       Function* calledFunc = it2->second=>getFunction();
>
>       cerr << ”function: “ << calledFunc->getName().str() <<"\n";  *//
> crash some times*
>
>       ... ...
>
>       ... ...
>
>     }
>
> }
>
>
>
> I found that some time "calledFunc" is NULL function and thus the output
> crash. I don't known why? If the before code is wrong, so what is the
> correct method for get all the called functions?
>
>
>
> I use LLVM 3.6. Thank you all in advance.
>
>
> --------------------------------------------
> Qiuping Yi
> Institute Of Software
> Chinese Academy of Sciences
>
>
>
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