[llvm-dev] function call replacement

Tue Jun 21 03:51:06 PDT 2016

Hi again,

that's weird... I continued the implementation of the replaced function
(not touched the FunctionPass, just the runtime function) and I have no
more the "*** Error in `lli': corrupted double-linked list: 0xaddress ***"
error message when I run the linked bitcode file...

Anyway the issue of the null pointer iterator still is here but now I
assume it doesn't imply the error in lli?

Hope you have any lead on that point,
Pierre

On 21 June 2016 at 09:10, Pierre Gagelin <Pierre.Gagelin at myport.ac.uk>
wrote:

> Hi,
>
> Thanks both of you for the help. I just missed that Create function had
> many optional arguments... sorry for that. However my problem wasn't coming
> from here (IRBuilder CreateCall function still return a pointer to CallInst
> so I just added 2 times the call?). I didn't wanted to detail the all issue
> previously because I knew I had a problem with my syntax. So here's my
> problem:
>
> I am doing this replacement operation in a FunctionPass (this is no
> restriction, I could do it on a ModulePass if that's a solution). On each
> Function given I do an iteration over the instructions and replace (if it's
> a call to the right function) the call. It's like this:
>
> bool FDPFunction::runOnFunction(Function &F) {
>   bool res = false;
>   TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
>
>   for (inst_iterator i = inst_begin(F), e = inst_end(F); i != e; ++i) {
>     Instruction *I = &*i;
>
>     if (!I) {
>       errs() << "error: null pointer instruction\n";
>       break;
>     } else if (isMyFunctionCall(I, TLI)) {
>       errs() << "found a call to the function to replace\n";
>       res = true;
>       replacement_function(I);
>     } else {
>       errs() << "default: trash instruction\n";
>     }
>   }
>
>   return res;
> }
>
> The problem is that after the first replacement, the iterator becomes a
> null pointer. With the break instruction the program is correctly
> instrumented for the first call (about that: what is the use of
> replaceAllUsesWith function? I thought it would replace all uses of the
> function... but just one is done). I can then link it and execute with lli
> (I still get a: "*** Error in `lli': corrupted double-linked list:
> 0xaddress ***" but after the whole execution is done).
>
> But if I remove the break and the if condition associated, well I get a
> null pointer exception : Assertion `Val && "isa<> used on a null pointer"'
> failed
>
> I tried to clone the current instruction to not modify the iterator but
> the ReplaceInstWithInst will cause troubles (probably because a copied
> instruction has no parents):
>
> #0 0x0000000002a95b5c llvm::sys::PrintStackTrace(llvm::raw_ostream&)
> /home/pierre/Desktop/llvm/lib/Support/Unix/Signals.inc:400:0
> #1 0x0000000002a95edf PrintStaI tried to clone the current instruction to
> not modify the iterator but the ReplaceInstWithInst will cause
> troublesckTraceSignalHandler(void*)
> /home/pierre/Desktop/llvm/lib/Support/Unix/Signals.inc:468:0
> #2 0x0000000002a94145 llvm::sys::RunSignalHandlers()
> /home/pierre/Desktop/llvm/lib/Support/Signals.cpp:44:0
> #3 0x0000000002a953a8 SignalHandler(int)
> /home/pierre/Desktop/llvm/lib/Support/Unix/Signals.inc:254:0
> #4 0x00007fe358d3dd10 __restore_rt
> (/lib/x86_64-linux-gnu/libpthread.so.0+0x10d10)
> #5 0x00000000011fe489 llvm::iplist<llvm::Instruction,
> llvm::SymbolTableListTraits<llvm::Instruction>
> >::insert(llvm::ilist_iterator<llvm::Instruction>, llvm::Instruction*)
> /home/pierre/Desktop/llvm/include/llvm/ADT/ilist.h:415:0
> #6 0x0000000002abc20d llvm::ReI tried to clone the current instruction to
> not modify the iterator but the ReplaceInstWithInst will cause
> troublesplaceInstWithInst(llvm::SymbolTableList<llvm::Instruction>&,
> llvm::ilist_iterator<llvm::Instruction>&, llvm::Instruction*)
> /home/pierre/Desktop/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp:198:0
> #7 0x0000000002abc2a5 llvm::ReplaceInstWithInst(llvm::Instruction*,
> llvm::Instruction*)
> /home/pierre/Desktop/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp:210:0
>
> Any idea on what could be the cause of the null pointer and how to avoid
> it?
>
> Thanks a lot for your time!
> Pierre
>
>
> On 20 June 2016 at 15:45, John Criswell <jtcriswel at gmail.com> wrote:
>
>> On 6/20/16 6:17 AM, Pierre Gagelin via llvm-dev wrote:
>>
>> Hi everyone,
>>
>> I am trying to replace the call of a certain function with a call to
>> another function. It would for example replace the following:
>>
>> %call = tail call noalias i8* @func(i64 10)
>> by
>> %call = tail call noalias i8* @other_func(i64 10)
>>
>> I managed to declare other_func correctly but I am having troubles to
>> understand how I should proceed to do the replacement.
>>
>> I tried to use ReplaceInstWithInst function as follows:
>>
>> CallInst *call_to_other_func_inst =
>> IRBuilder.CreateCall(ptr_to_other_func, args);
>> ReplaceInstWithInst(call_to_func_inst, newI);
>>
>> LLVM builds correctly but the instrumentation crashes at optimization
>> time. I know this isn't the correct way to do it because IRBuilder
>> generates IR and I just want to have an instance of a CallInst. But I don't
>> see how it is supposed to be done?
>>
>>
>> Do you have assertions enabled?  If so, is the crash an assertion failure
>> and, if so, which assertion is failing?  It's nearly impossible to tell
>> what the problem is just by knowing that it is crashing.
>>
>>
>> There are methods to create CallInst in the Instruction.h file but those
>> needs to give an inserting point. Shoud I insert the call to other_func
>> before the one to func and just remove the call instruction to func?
>>
>>
>> Yes.  You need to place the new call instruction within the same basic
>> block as the old call instruction.  Placing it right before the old call
>> instruction is a good place.
>>
>> The code that Ashutosh provided is what I'd use to do what you're doing.
>>
>> Regards,
>>
>> John Criswell
>>
>>
>> Thanks for your help,
>> Pierre
>>
>>
>> _______________________________________________
>> LLVM Developers mailing listllvm-dev at lists.llvm.orghttp://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>>
>>
>> --
>> John Criswell
>> Assistant Professor
>> Department of Computer Science, University of Rochesterhttp://www.cs.rochester.edu/u/criswell
>>
>>
>
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