[llvm-dev] Writing a test for gcov style coverage crashing after dlclose

[Benoit Belley via llvm-dev]

Excellent! Thanks for the guidance. I’ll follow your suggestion.


Cheers,
Benoit

On 16-04-07 20:03, "vsk at apple.com on behalf of Vedant Kumar"
<vsk at apple.com> wrote:

>Hi Benoit,
>
>> Now, I¹d like to include a test program to demonstrate the fix. AFAICT,
>> there seems to be a single test for
>> "-fprofile­arcs/-ftest-coverage/-femit-coverage-data", namely:
>> tools/clang/test/CodeGen/code-coverage.c. (To be fair, there are some
>> tests related to the testing of the command line options themselves.)
>> There seems to be no tests that actually execute the instrumented
>> executables to gather coverage data.
>> 
>> - Is that a fair assessment of the current situation ?
>
>Yes, I think that's fair.
>
>
>> - Should I create a new test directory such as
>> llvm/projects/compiler-rt/test/gcov (or gcda) to put my test case ?
>
>I think such a test could live in, e.g,
>compiler-rt/test/profile/gcda-$foo.
>
>The integration tests for profiling instrumentation and code coverage also
>live in this directory.
>
>thanks
>vedant
>
>
>> 
>> Guidance would be appreciated.
>> Benoit
>> 
>> ‹‹‹‹‹‹‹‹‹‹‹‹‹‹‹‹‹‹‹‹
>> 
>> See: https://llvm.org/bugs/show_bug.cgi?id=27224
>> 
>> 
>> Bug 27224 <https://llvm.org/bugs/show_bug.cgi?id=27224> - gcov /
>> gcda-based profiling crashes when shared libraries are unloaded
>>(dlclose())
>> 
>> 
>> I believe that GCDA profiling functions should be declared as hidden,
>>i.e.
>> symbols that are not exported by shared libraries. This would allow the
>> GCDA based profiling to work correctly with code using dlopen/dlclose to
>> load and unload shared libraries.
>> 
>> Each shared library must have its own copy of the following GCDA
>>functions:
>> 
>>     - __gcov_flush
>>     - llvm_delete_flush_function_list
>>     - llvm_delete_writeout_function_list
>>     - llvm_gcda_emit_arcs
>>     - llvm_gcda_emit_function
>>     - llvm_gcda_end_file
>>     - llvm_gcda_increment_indirect_counter
>>     - llvm_gcda_start_file
>>     - llvm_gcda_summary_info
>>     - llvm_gcov_init
>>     - llvm_register_flush_function
>>     - llvm_register_writeout_function
>>     - llvm_writeout_files
>> 
>> Defining these function as "hidden" prevents a shared library from
>> exporting them in its interface. The end-result is that each profiled
>> shared library will be guaranteed to get its own set of the GCDA
>>functions
>> extracted from libclang_rt.profile.a.
>> 
>> These GCDA functions are referencing the static writeout_fn and flush_fn
>> lists. These lists are traversed when a shared library is unloaded or
>>the
>> program exits through an atexit() function. It is important that each
>> shared library gets its own set of these lists so that the proper .gcda
>> files are updated when a library is unloaded.
>> 
>> Furthermore, if a shared library doesn't get its own set of GCDA
>> functions and associated lists, it will leave dangling pointers to its
>>own
>> "writeout" and "flush" functions in the static writeout_fn and flush_fn
>> lists of another shared library. These dangling pointers lead to crashes
>> when the other shared library is unloaded or when the program exits.
>> 
>> 
>> 
>> ‹‹‹‹‹‹‹‹‹‹‹‹‹‹
>> 
>> 
>> Benoit Belley
>> Sr Principal Developer
>> M&E-Product Development Group
>> Autodesk, Inc.
>> 10 Duke Street
>> Montreal, Quebec, Canada H3C 2L7
>> www.autodesk.com <http://www.autodesk.com/>
>> 
>> 
>> 
>> 
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