[llvm-dev] Using TSAN along with custom llvm IR pass
Nischai Vinesh via llvm-dev
llvm-dev at lists.llvm.org
Mon Jul 10 06:00:17 PDT 2017
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
> > I think the code is not getting instrumented with tsan at all. In the
> > 3', when I instrument it using 'opt -tsan ...', it gives a warning
> > You're attempting to print out a bitcode file." I guess this method
> > 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
> > 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
> >> > 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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