http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55916
Bug #: 55916
Summary: Alignment issues with real(16) on i686
Classification: Unclassified
Product: gcc
Version: 4.8.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: fortran
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: ja...@gcc.gnu.org
The following testcase with -m32 -msse4 -g -O3 -fno-inline may segfault
(depending on whether malloc returns just 8-byte or 16-byte aligned pointer).
real(16), allocatable :: aaaa(:)
real(16) :: x(10)
integer :: i,n=10
allocate(aaaa(n))
do i = 1,n
aaaa(i) = 8.0
enddo
call foo (aaaa)
deallocate(aaaa)
contains
subroutine foo (aaaa)
real(16), allocatable :: aaaa(:)
aaaa(1) = aaaa(1) + 1
end subroutine
end
The problem is that __float128 aka real(16) has alignment 128 bits, but on
i686-linux malloc only guarantees 64 bit alignment (2 * sizeof (void *) byte
alignment). As __float128 is outside of the scope of C/C++, this is not a bug
on the C library side.
Guess for real(16) allocatables or any allocatables that require alignment
bigger than that of standard types Fortran should use posix_memalign (or
perhaps some libgfortran wrapper) that will be passed not just the size to
allocate, but also required alignment.
