https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83649
Bug ID: 83649
Summary: Large reads fail
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libfortran
Assignee: unassigned at gcc dot gnu.org
Reporter: jb at gcc dot gnu.org
Target Milestone: ---
Consider the testcase
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
This fails on x86_64-pc-linux-gnu with
./a.out
At line 10 of file largewr.f90 (unit = 10, file = 'largewr.dat')
Fortran runtime error: End of file
[snip]
The reason is that Linux never reads or writes more than 2,147,479,552 bytes in
a single syscall. For write libgfortran does the writing in a loop, and it's
handled correctly, but for read we cannot do that loop since then it will hang
when reading from the terminal where short reads are perfectly Ok.
