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GCC GSOC 2019


Hi,

I am Shubham Narlawar. Currently, I am a Computer Engineering undergrad
student at Pune University, India. I am interested in contributing to GCC
for GSOC 2019.

We have done a project from GCC GSOC 2018 idea list which is implementing
Csmith fuzzer leveraging GCC C Extensions under the guidance of Andi Kleen.

Csmith is a C fuzzer which generates standard C code but no extensions. We
implemented few of GCC C extensions in Csmith (which now we call it as
"Extended Csmith"). Extended Csmith is now able to fuzz extensions along
with standard C code.

Following GCC C Extensions are implemented in Csmith currently -
1. Labels as Values (Computed Goto)
2. Local Labels
3. Typeof
4. __int128 - Signed and unsigned integer of size 128 bits.
5. Cast to Union
6. Label attributes - hot cold
7. Variable attributes - a) aligned
                                    b) unused
                                    c) section
8. Binary constants
9. Statement Expression

10. Transactional memory relaxed - tm_relaxed (not a GCC C extension)

Note - Different Combinations of these extensions can be used while
generating random C code using extended csmith.

Here is the github link of the project.
https://github.com/Sameeranjoshi/csmith/tree/gcc-extensions

Currently, We are running extended csmith on gcc10 of GCC Compile Farm
Project and found following bugs -
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89135
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89153
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87118
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89223

We expect to find more bugs in GCC as the gcc compiler is being stress
tested now.

Code coverage - Csmith vs Extended Csmith

 Csmith i.e. [without gcc extn ]
  line - 35.2
  function - 43.2
  branch - 25.7

  Extended Csmith [with gcc extn]
  line - 35.7
  function - 43.9
  branch - 26.1

  %gain
  line - 0.5%
  function - 0.7%
  branch - 0.4%

For GSOC 2019, I am proposing below project idea -

Implementation of following extensions in the Csmith -
1. Function attributes - aligned, alloc_align, always_inline, hot, cold,
deprecated, nothrow, used, etc
2. Vector extensions
3. Transactional Memory extensions
4. Type attributes
and remaining GCC C extensions.

Benefits to GCC -
1. Increased code coverage.
2. There is a possibility of finding more bugs after adding the above
extensions.

Thanks and Regards.
Shubham Narlawar


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