Re: wordcopy.c segfault on external function call

[Ian Lance Taylor <iant at google dot com>]

David Mebane <mebane@gatech.edu> writes:

> The following code extest.cpp:
>
> extern "C" { int ilaenv_( int *ispec, const char *name, const char
> *uplo, int *N, int *N2, int *N3, int *N4 ); }
>
> int main ()
> {
>   int ispec = 1;
>   const char* name = 'DSYTRD';
>   const char uplo = 'U';
>   int N = 4;
>   int N2 = -1;
>   int N3 = -1;
>   int N4 = -1;
>   int NB;
>
>   NB = ilaenv_( &ispec, name, &uplo, &N, &N2, &N3, &N4 );
>
>   return 0;
>
> }
>
> compiled with:
>
> g++ -ggdb -L/.../lapack/ extest.cpp -llapack -lblas -lgfortran
>
> using g++ 4.4.1, when run under gdb, segfaults at the external
> function call, giving:
>
> Program received signal SIGSEGV, Segmentation fault.
> _wordcopy_bwd_aligned (dstp=140737353957304, srcp=-130065848,
> len=2305843009196895680) at wordcopy.c:282
>
> the backtrace yields:
>
> #0  _wordcopy_bwd_aligned (dstp=140737353957304, srcp=-130065848,
> len=2305843009196895680) at wordcopy.c:282
> #1  0x00007ffff709ccaa in memmove (dest=0x7fffffffd1f0, src=<value
> optimized out>, len=18446744073575165448) at memmove.c:99
> #2  0x000000000040f7c1 in ilaenv_ ()
> #3  0x00007fffffffda90 in ?? ()
> #4  0x00007fffffffdbf0 in ?? ()
> #5  0x0000000000000002 in ?? ()
> #6  0x00007fffffffdbf0 in ?? ()
> #7  0x00007fffffffd25f in ?? ()
> #8  0x00007fffffffda60 in ?? ()
> #9  0x0000000000000000 in ?? ()
>
> I have only a faint idea of what wordcopy.c does, but I'm guessing
> that the length parameter here is perhaps a bit large.  I thought I'd
> post here in case there's a known issue with wordcopy.c.

Forget wordcopy.c.  It's just a subroutine of memmove, which is a
standard function.  The problem here is that memmove is being called
with a very very large length.  It's impossible for us to tell you
anything about why that is happening, because you haven't shown us the
source code for ilaenv_, which is the function that is calling memmove.

Ian