[petsc-dev] clang --analyze messages on PETSc

Barry Smith bsmith at mcs.anl.gov
Tue Apr 14 17:11:25 CDT 2015

  Jed suggested just passing requests for zero length malloc to malloc() and free() (claim is standards require them to behave properly  now a days) and remove all zero length checking from the macros. Will this resolve everything? Note that we need to pass a flag to --analyze telling it that zero length mallocs are ok otherwise it will generate some messages about them.


> On Apr 14, 2015, at 3:33 AM, Lisandro Dalcin <dalcinl at gmail.com> wrote:
> On 14 April 2015 at 02:46, Matthew Knepley <knepley at gmail.com> wrote:
>> On Mon, Apr 13, 2015 at 5:48 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
>>> When I run clang --analyze on PETSc on getting warnings of the type below,
>>> any idea how to deal with them? Clearly these things are usually not null
>>> pointers or PETSc would crash everywhere.
>> Lisandro brought this up.
>> This is a problem with the analyzer. Anything that uses PetscMallocK() will
>> be wrong since it can
>> possibly be NULL. The limitations of static analysis are stark.
> There is a way to silent many of these false positives:
> 1) First we need to solve the differences between PetscMalloc() and
> PetscMallocK() regarding zero-size allocations.
> 2) PetscMalloc1() is by far the most used of all the PetscMallocK()
> routines. So we should make PetscMalloc1() a direct call to
> PetscMalloc() (no checks for zero-sized allocs) and modify
> PetscMalloc() to handle zero-sized allocations by setting the pointer
> to NULL.
> These simple changes will remove tons of "null pointer dereference"
> false positives, and also fix the inconsistent behavior between
> PetscMalloc() and PetscMallocK().
> -- 
> Lisandro Dalcin
> ============
> Research Scientist
> Computer, Electrical and Mathematical Sciences & Engineering (CEMSE)
> Numerical Porous Media Center (NumPor)
> King Abdullah University of Science and Technology (KAUST)
> http://numpor.kaust.edu.sa/
> 4700 King Abdullah University of Science and Technology
> al-Khawarizmi Bldg (Bldg 1), Office # 4332
> Thuwal 23955-6900, Kingdom of Saudi Arabia
> http://www.kaust.edu.sa
> Office Phone: +966 12 808-0459

More information about the petsc-dev mailing list