When running gfortran on a 64-bit AMD Athlon64 Linux machine, the
Fortran ALLOCATE statement does not align pointers on 16-byte boundaries.
This means that allocated memory cannot be passed to assembly language
routines that rely on 16-byte alignment (e.g. assembly language using
SSE instructions like "movaps").
The demonstration below involves two files, the first one
a Fortran program name try.f which allocates an array x.
It calls a C function, shown in file sub.c, which returns the
address of x, and prints a message saying whether or not the
array is 16-byte aligned.
% gfortran -v
Using built-in specs.
Target: x86_64-unknown-linux-gnu
Configured with: ../gcc/configure --prefix=/var/tmp/gfortran-20050916/irun
--enable-languages=c,f95
Thread model: posix
gcc version 4.1.0 20050916 (experimental)
% cat try.f
real, allocatable :: x(:)
integer*8 address, p, sixteen
external address
sixteen = 16
allocate (x(300000))
p = address(x)
write (*,99) 'Address of x = ', p
99 format (1x,a,'0x',z16.16)
if (mod(p,sixteen) .eq. 0) then
write (*,*) 'x is aligned on a 16-byte boundary'
else
write (*,*) 'x is not aligned on a 16-byte boundary'
end if
end
% cat sub.c
unsigned long address_(void *x)
{
return (unsigned long)x;
}
% gfortran try.f sub.c
% ./a.out
Address of x = 0x00002AAAAB1CB028
x is not aligned on a 16-byte boundary
--
Summary: gfortran ALLOCATE statement does not align objects on
16-byte boundary
Product: gcc
Version: 4.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: fortran
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: mick at nag dot co dot uk
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24261
