Re: seekable stdin test failure on OS X

[Gary V. Vaughan]

Hi Eric,

On 2 Apr 2007, at 13:20, Eric Blake wrote:
> According to Gary V. Vaughan on 3/28/2007 10:47 AM:
> > $ make check TESTSUITEFLAGS='-v 68'
> > 68. others.at:458: testing ...
> > ../../tests/others.at:467: m4 -b -d  < in.m4
> > --- -   2007-03-28 17:36:35.000000000 +0100
> > +++
> > /Users/gary/Devo/Source/m4--devo--0/+build/tests/testsuite.dir/at- 
> > stdout
> > 2007-03-28 17:36:35.000000000 +0100
> > @@ -1,2 +1 @@
> > -m4exit(15)
> > ../../tests/others.at:467: exit code was 15, expected 0
> > 68. others.at:458:  FAILED (others.at:467)
>
> > I don't know what is being tested here, so I can't debug any further.
>
> Yuck.  I think this means that on your platform, fflush(stdin) is
> neglecting to reset the underlying fd position when stdin is seekable,
> which is a bug in your libc.  To confirm, do you have anything like  
> strace
> or truss that you could run to see what syscalls took place?

Yes, there is ktrace which outputs the following when running test 68:

  6760 m4       GIO   fd 0 read 24 bytes
       "syscmd(`cat')m4exit(15)
       "
  6760 m4       RET   read 24/0x18
  6760 m4       CALL  lseek(0,0,0x1)
  6760 m4       RET   lseek 24/0x18
  6760 m4       CALL  sigaction(0x2,0xbfffece0,0xbfffed3c)
  6760 m4       RET   sigaction 0
  6760 m4       CALL  sigaction(0x3,0xbfffece0,0xbfffed30)
  6760 m4       RET   sigaction 0
  6760 m4       CALL  sigprocmask(0x1,0xbfffed58,0xbfffed54)
  6760 m4       RET   sigprocmask 0
  6760 m4       CALL  fork
  6760 m4       RET   fork 6777/0x1a79
  6760 m4       CALL  wait4(0x1a79,0xbfffed5c,0,0)
  6760 m4       RET   wait4 6777/0x1a79
  6760 m4       CALL  sigaction(0x2,0xbfffece0,0)
  6760 m4       RET   sigaction 0
  6760 m4       CALL  sigaction(0x3,0xbfffece0,0)
  6760 m4       RET   sigaction 0
  6760 m4       CALL  sigprocmask(0x3,0xbfffed54,0)
  6760 m4       RET   sigprocmask 0
  6760 m4       CALL  fstat(0x1,0xbfffecc0)
  6760 m4       RET   fstat 0
  6760 m4       CALL  fstat(0x2,0xbfffec60)
  6760 m4       RET   fstat 0
  6760 m4       CALL  lseek(0,0,0x1)
  6760 m4       RET   lseek 24/0x18
  6760 m4       CALL  close(0x1)
  6760 m4       RET   close 0
  6760 m4       CALL  close(0x2)
  6760 m4       RET   close 0
  6760 m4       CALL  exit(0xf)

The fork and wait must be the syscmd, and the lseek(0,0,0x1) that  
returns
24 is the seek on stdin from fflush.  What does that mean though?

> We may end up having to write an autoconf test that can detect this
> brokenness in libc, and based on that test, add additional calls to  
> fseek
> if using fflush alone is inadequate for m4 to follow the POSIX  
> rules of
> how to handle seekable input streams.

Bleh!

Cheers,
        Gary
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