[Bug driver/34280] New: using -o with -MM produces truncated output with multiple input files

["vapier at gentoo dot org" <gcc-bugzilla at gcc dot gnu dot org>]

trying to do something simple like:
$ gcc -MM one.c two.c three.c -o .depend

results in .depend only containing the information from the last file processed
as each file processed causes the output to be opened/closed with O_TRUNC

$ cat .depend
three.o: three.c

$ strace -f -eopen gcc -MM one.c two.c three.c -o .depend 2>&1 | grep
'\.depend'
28900 open(".depend", O_WRONLY|O_CREAT|O_TRUNC, 0666) = 3
28901 open(".depend", O_WRONLY|O_CREAT|O_TRUNC, 0666) = 3
28902 open(".depend", O_WRONLY|O_CREAT|O_TRUNC, 0666) = 3

a quick compare shows 3.3.6 - 4.3.0 all behaving this way


-- 
           Summary: using -o with -MM produces truncated output with
                    multiple input files
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: driver
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: vapier at gentoo dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34280