https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83649
--- Comment #2 from Janne Blomqvist <jb at gcc dot gnu.org> --- Author: jb Date: Tue Jan 2 13:25:10 2018 New Revision: 256074 URL: https://gcc.gnu.org/viewcvs?rev=256074&root=gcc&view=rev Log: PR libgfortran/83649 Chunk large reads and writes It turns out that Linux never reads or writes more than 2147479552 bytes in a single syscall. For writes this is not a problem as libgfortran already contains a loop around write() to handle short writes. But for reads we cannot do this, since then read will hang if we have a short read when reading from the terminal. Also, there are reports that macOS fails I/O's larger than 2 GB. Thus, to work around these issues do large reads/writes in chunks. The testcase from the PR program largewr integer(kind=1) :: a(2_8**31+1) a = 0 a(size(a, kind=8)) = 1 open(10, file="largewr.dat", access="stream", form="unformatted") write (10) a close(10) a(size(a, kind=8)) = 2 open(10, file="largewr.dat", access="stream", form="unformatted") read (10) a if (a(size(a, kind=8)) == 1) then print *, "All is well" else print *, "Oh no" end if end program largewr fails on trunk but works with the patch. Regtested on x86_64-pc-linux-gnu, committed to trunk. libgfortran/ChangeLog: 2018-01-02 Janne Blomqvist <j...@gcc.gnu.org> PR libgfortran/83649 * io/unix.c (MAX_CHUNK): New define. (raw_read): For reads larger than MAX_CHUNK, loop. (raw_write): Write no more than MAX_CHUNK bytes per iteration. Modified: trunk/libgfortran/ChangeLog trunk/libgfortran/io/unix.c
