------- Comment #30 from tkoenig at gcc dot gnu dot org 2007-12-02 20:11
-------
(In reply to comment #25)
> Created an attachment (id=14682)
--> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=14682&action=view) [edit]
> New patch, clean fix.
Yes, this looks clean and self-contained (and something we can safely
incorporate into 4.3).
Although not strictly a regression-fix, I think this should also
be considered for 4.2.
This is now regtesting on my machine.
> Answer to comment #18, Thomas, the flush is needed for streamio_12.f90 where
> we
> use a write(10, pos=1) to reposition the file somewhere far from the current
> buffer contents.
I understand that. What I meant to ask is: Why do we
still flush for formatted stream I/O?
> Status since comment#24. Two regressions have led me to back away and take a
> different approach. I would still like to revisit the unix.c internals later.
Probably not in time for 4.3, but this should be on the list for 4.4
(unless we stumble across a bug). I'll try some stress-tests :-)
In general: Your patch does the right thing for both reading and
writing, as evidenced by the strace log:
$ cat readwrite.f90
program main
implicit none
integer :: i
integer(kind=1) r
open(95,form="unformatted",access="stream")
do i=0,10
write(95) int(i,kind=1)
end do
close (95)
open(95,form="unformatted",access="stream")
do i=0,10
read(95) r
end do
end program main
$ gfortran readwrite.f90
$ strace -e write,read,_llseek ./a.out
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0`\311\0"..., 512) = 512
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0`4\0\000"..., 512) =
512
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0\360\30"..., 512) = 512
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0\260a\1"..., 512) = 512
_llseek(0, 0, 0xbff954a0, SEEK_CUR) = -1 ESPIPE (Illegal seek)
_llseek(1, 0, 0xbff95490, SEEK_CUR) = -1 ESPIPE (Illegal seek)
_llseek(2, 0, 0xbff95490, SEEK_CUR) = -1 ESPIPE (Illegal seek)
_llseek(3, 0, [0], SEEK_CUR) = 0
write(3, "\0\1\2\3\4\5\6\7\10\t\n", 11) = 11
_llseek(3, 0, [0], SEEK_CUR) = 0
read(3, "\0\1\2\3\4\5\6\7\10\t\n", 8192) = 11
read(3, "", 8181) = 0
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33985
