| Issue |
208669
|
| Summary |
[Flang] -flto silently truncates COMMON block size past 4 GB
|
| Labels |
|
| Assignees |
|
| Reporter |
ejose02
|
With -flto, flang silently miscompiles programs whose Fortran COMMON block exceeds 2³² bytes (~4 GB).
Expected behavior: The full COMMON size is preserved through link, and in-bounds stores complete without faulting.
Actual behavior: The COMMON symbol's ELF size is truncated to the low 32 bits of the true size, so less memory is reserved than declared. Stores past that point segfault at runtime, with no compile-time or link-time diagnostic. Without -flto, the full size is retained and the program runs correctly.
Reproducer:
```Fortran
program repro
implicit none
integer, parameter :: idim = 1501000
integer, parameter :: idim2 = idim + 1
integer, parameter :: nbig = 400 * idim2
integer, parameter :: nmed = nbig / 10
integer, parameter :: nlist = idim
integer :: iamawk(nbig), ijvarcomp(nbig)
integer :: ivarawk(nmed), jvarawk(nmed)
integer :: ivarawkcomp(nmed), iamindex(nmed)
integer :: j_offset(idim+1)
integer :: icompactlist(nlist)
integer :: jvarawkcomp(nlist), icclist(nlist), irealcomp(nlist)
common /big/ iamawk, ijvarcomp, ivarawk, jvarawk, ivarawkcomp, iamindex, &
j_offset, icompactlist, jvarawkcomp, icclist, irealcomp
integer :: ipart
iamawk(1) = 1
iamawk(nbig) = 2
ijvarcomp(1) = 3
ipart = 750457
call touch_past_4gb(ipart)
print *, 'TEST PASSED'
contains
subroutine touch_past_4gb(ipart)
integer, intent(in) :: ipart
icompactlist(ipart) = 3
end subroutine
end program
```
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