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(C) 2007 guidod
Download the M4 Source.


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Guido U. Draheim <>


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guidod's C Support (released)


The libtool 1.4.x processing (and patched 1.3.5) uses a little "impgen" tool to turn a "*.dll" into an import "*.lib" as it is needed for win32 targets. However, this little tool is not shipped by binutils, it is not even a command option of dlltool or dllwrap. It happens to be a C source snippet implanted into the libtool sources - it gets written to ".libs", compiled into a binary on-the-fly, and executed right away on the "dll" file to create the import-lib (dll.a files in gcc-speak).

This mode works fine for a native build within mingw or cygwin, but it does not work in cross-compile mode since CC is a crosscompiler

  • - it will create an .exe file on a non-win32 system, and as a

result an impgen.exe is created on-the-fly that can not be executed on-the-fly. Luckily, the actual libtool snippet uses HOST_CC to compile the sources which has a fallback to CC when the HOST_CC variable was not set.

this ac-macro is trying to detect a valid HOST_CC which is not a cross-compiler. This is done by looking into the $PATH for a "cc" and the result is patched into libtool a HOST_CC, iow it adds another configured variable at the top of the libtool script.

In discussions on the libtool mailinglist it occurred that later gcc/binutils generations are able to link with dlls directly, i.e. there is no import-lib needed anymore. The import-table is created within the linker itself (in-memory) and bound to the .exe/.dll currently in the making. The whole stuff of impgen exe and compiling it on-the-fly, well, it is superflouos then.

Since mingw crosscompilers tend to be quite a fresh development it was agreed to remove the impgen stuff completly from libtool sources. Still however, this macro does not hurt since it does not patch impgen cmds but it just adds HOST_CC which might be useful in other cross-compiling cases as well. Therefore, you can leave it in for maximum compatibility and portability.

M4 Source Code
[# patch libtool to add HOST_CC sometimes needed in crosscompiling a win32 dll
if grep "HOST_CC" libtool &gt;/dev/null; then
  if test "$build" != "$host" ; then
    if test "_$HOST_CC" = "_" ; then
      for i in `echo $PATH | sed 's,:, ,g'` ; do
      test -x $i/cc &amp;&amp; HOST_CC=$i/cc
AC_MSG_RESULT(patching libtool to add HOST_CC=$HOST_CC)
    test -f libtool.old || (mv libtool libtool.old &amp;&amp; cp libtool.old libtool)
    sed -e "/BEGIN.*LIBTOOL.*CONFIG/a\\
HOST_CC=$HOST_CC" libtool &gt;
    (test -s || rm 2&gt;/dev/null
    test -f &amp;&amp; mv libtool # not 2&gt;/dev/null !!
    test -f libtool     || mv libtool.old libtool