Hello,
I think I have run into an inconsistency between the documented behaviour of LAPACK subroutine ZHEEVR and the observed behaviour.
According to the documentation here:
https://software.intel.com/en-us/mkl-developer-reference-fortran-heevr
the input array "isuppz" is "[r]eferenced only if eigenvectors are needed (jobz = 'V') and all eigenvalues are needed."
However, it appears that the array is accessed even if
1. the "jobz" parameter is 'N' (that is, only the eigenvalues are requested, while the eigenvectors are not); or
2. the "jobz" parameter is 'V', and only a proper subset of eigenvalue/vectors is requested, as specified by the "il" and "iu" parameters.
The uploaded files "demos1.f" and "demos2.f" demonstrate these problems respectively. In each demo, the subroutine zheevr() is called on the 6x6 identity matrix. Before the call, the input "isuppz" array is filled with an integer pattern. If the implementation matches the documentation, these initial values should not change upon return from zheevr(). But here, the output shows that the isuppz array did get overwritten by zheevr().
That is, the expected output, for both demo programmes, should be:
m: 3
isuppz:
111111 222222 333333 444444 555555 666666 777777 888888 999999 101010 101101 102102
but the actual output was:
m: 3
isuppz:
0 0 0 0 0 0 777777 888888 999999 101010 101101 102102
This means that the array may get overwritten when it is not expected to be. In the case when the caller expects isuppz to be not referenced, and therefore passes a small array (maybe to save memory space), the call to zheevr may cause a memory error or buffer overflow.
I wish to bring this observation to the attention of the Intel staff here. Thanks!
Zoë
- Operating system and version
-- macOS 10.15.3
- Library version
-- MKL 2020.0 (distributed with miniconda)
- Compiler version
-- gfortran 9.3.0
- Steps to reproduce the error
-- The Fortran77 code (attached) was compiled and linked with "-lmkl_rt"
