[llvm-dev] Using TSAN along with custom llvm IR pass

[Nischai Vinesh via llvm-dev]

Oh ok. 
But is there any dependency when I change to this method, other than the 
way the pass is registered? Because when I used clang along with -Xclang to 
run the pass on the program, it is crashing!




On Monday, July 10, 2017 at 1:09:43 PM UTC+2, Dmitry Vyukov wrote:
>
> On Mon, Jul 10, 2017 at 1:06 PM, Nischai Vinesh 
> <nischai... at gmail.com <javascript:>> wrote: 
> > I think the code is not getting instrumented with tsan at all. In the 
> 'step 
> > 3', when I instrument it using 'opt -tsan ...', it gives a warning 
> "WARNING: 
> > You're attempting to print out a bitcode file." I guess this method 
> doesn't 
> > instrument the code. 
> > 
> > Is there any other way I can instrument the code with tsan? 
>
>
> One option is to add your pass to llvm and execute clang with 
> -fsanitize=thread. 
>
>
> > On Monday, July 10, 2017 at 7:21:28 AM UTC+2, Dmitry Vyukov wrote: 
> >> 
> >> On Sun, Jul 9, 2017 at 3:50 PM, Nischai Vinesh <nischai... at gmail.com> 
> >> wrote: 
> >> > Hello, 
> >> > 
> >> > I tried that as well but there are no tsan warnings thrown at run 
> time, 
> >> > even 
> >> > though there are data race error! 
> >> > 
> >> > The steps I followed: 
> >> > 1. Generate bitcode using 'clang -emit-llvm' command 
> >> > 2. Using the 'opt -load ..' command, I instrumented the bitcode file 
> >> > with my 
> >> > custom pass 
> >> > 3. Using the command 'opt -tsan ..', instrumented the output bitcode 
> >> > file 
> >> > from step 2 
> >> > 4. Using the llvm backend compiler, 'llc', compiled the program to 
> >> > native 
> >> > assembly 
> >> > 5. The output from step 4 is compiled again with 'clang 
> >> > -fsanitize=thread' 
> >> > (linking tsan here) for the final object file. 
> >> > 
> >> > Executing this final output file works fine, except that it doesn't 
> >> > throws 
> >> > any TSAN warnings! 
> >> 
> >> 
> >> Hi Nischai, 
> >> 
> >> I see 3 possibilities: 
> >> 1. Either the code is somehow ends up being non-instrumented, or 
> >> 2. tsan does not consider what it sees a data race, or 
> >> 3. the data race is masked by unrelated synchronization. 
> >> 
> >> For 1 you can check that the resulting code in fact contains __tsan_* 
> >> callbacks. 
> >> For 2 and 3 you can rebuilt tsan runtime with TSAN_DEBUG_OUTPUT=2 
> >> define, then it will print everything it sees (memory accesses and 
> >> synchronization). This output will allow us to figure out why it does 
> >> not report a race. 
> > 
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