Re: mingw lseek bug

[Bruno Haible]

Eric Blake wrote:
> > It should be possible to write a real test.
> > ...
> > I still don't see a proof that lseek is incorrect on mingw.
> 
> I tested by writing test-lseek.c first, and using
> 
> echo hi | test-lseek && echo failed
> 
> then repeating that test with the benefit of the lseek module, and seeing
> the difference in output on mingw.  If test-lseek succeeds when stdin is a
> pipe, then it is an indication of a bug in lseek.
> ...
> How? Mingw doesn't provide pipe(), socket() is a bear to get right in a
> configure test, and I don't know how to coerce autoconf into guaranteeing
> that conftest's stdin is either a file or a pipe.

Thanks for the explanations. I added this test. The trick is to realize
that inside AC_LINK_IFELSE, you can use the compiled conftest program. And
even if that was not possible you could use this idiom:

cat > conftest.$ac_ext <<EOF
...
EOF
AC_TRY_EVAL([ac_link])
if test -s conftest$ac_exeext; then
  ... ./conftest$ac_exeext ...
else
  failed
fi

2007-05-28  Bruno Haible  <address@hidden>

        * m4/lseek.m4 (gl_FUNC_LSEEK): When not cross-compiling, perform a real
        runtime test.

*** m4/lseek.m4 24 May 2007 16:59:21 -0000      1.1
--- m4/lseek.m4 28 May 2007 12:33:02 -0000
***************
*** 1,4 ****
! # lseek.m4 serial 1
  dnl Copyright (C) 2007 Free Software Foundation, Inc.
  dnl This file is free software; the Free Software Foundation
  dnl gives unlimited permission to copy and/or distribute it,
--- 1,4 ----
! # lseek.m4 serial 2
  dnl Copyright (C) 2007 Free Software Foundation, Inc.
  dnl This file is free software; the Free Software Foundation
  dnl gives unlimited permission to copy and/or distribute it,
***************
*** 9,20 ****
    AC_REQUIRE([gl_UNISTD_H_DEFAULTS])
    AC_REQUIRE([AC_PROG_CC])
    AC_CACHE_CHECK([whether lseek detects pipes], [gl_cv_func_lseek_pipe],
!     [AC_COMPILE_IFELSE([AC_LANG_PROGRAM([#include <unistd.h>],
! [#if (defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__
  /* mingw mistakenly returns 0 when trying to seek on pipes.  */
    Choke me.
! #endif])],
!       [gl_cv_func_lseek_pipe=yes], [gl_cv_func_lseek_pipe=no])])
    if test $gl_cv_func_lseek_pipe = no; then
      gl_REPLACE_LSEEK
    fi
--- 9,40 ----
    AC_REQUIRE([gl_UNISTD_H_DEFAULTS])
    AC_REQUIRE([AC_PROG_CC])
    AC_CACHE_CHECK([whether lseek detects pipes], [gl_cv_func_lseek_pipe],
!     [if test $cross_compiling = no; then
!        AC_LINK_IFELSE([
! #include <sys/types.h> /* for off_t */
! #include <stdio.h> /* for SEEK_CUR */
! #include <unistd.h>
! int main ()
! {
!   /* Exit with success only if stdin is seekable.  */
!   return lseek (0, (off_t)0, SEEK_CUR) < 0;
! }],
!          [if test -s conftest$ac_exeext \
!              && ./conftest$ac_exeext < conftest.$ac_ext \
!              && { echo hi | ./conftest$ac_exeext; test $? = 1; }; then
!             gl_cv_func_lseek_pipe=yes
!           else
!             gl_cv_func_lseek_pipe=no
!           fi],
!          [gl_cv_func_lseek_pipe=no])
!      else
!        AC_LINK_IFELSE([
! #if (defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__
  /* mingw mistakenly returns 0 when trying to seek on pipes.  */
    Choke me.
! #endif],
!          [gl_cv_func_lseek_pipe=yes], [gl_cv_func_lseek_pipe=no])
!      fi])
    if test $gl_cv_func_lseek_pipe = no; then
      gl_REPLACE_LSEEK
    fi