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Date: Sat, 02 Aug 2008 09:46:08 -0700
From: Brian Dessent <brian AT dessent DOT net>
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To: r <r DOT trev_ AT inwind DOT it>
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Subject: Re: Compile
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r wrote:

> I'm trying to compile a wonderful program ( command line ) to grab
> videoes from youtube. It needs newt, a little utility. But when I try to
> compile this utility I have the follewing errors :
> ...
> snackmodule.c:126: error: initializer element is not constant
> snackmodule.c:126: error: (near initialization for `snackGridType.ob_type')
> snackmodule.c:168: error: initializer element is not constant
> snackmodule.c:168: error: (near initialization for `snackFormType.ob_type')
> snackmodule.c:255: error: initializer element is not constant
> snackmodule.c:255: error: (near initialization for `snackWidgetType.ob_type')
> make: *** [_snackmodule_la-snackmodule.lo] Error 1
> 
> Do you know if it is an unrecoverable error ( a limitation of cygwin )
> that will not permit to install this utility ?

In the future, you could save a lot of time on the part of people that
might wish to help you by either pasting the contents of the above
mentioned lines or providing a link to the source tarball.  Or at the
very least specify the version you're trying to build.  Also, a proper
subject usually helps.

The offending construct is this:

static PyTypeObject snackFormType = {
        PyObject_HEAD_INIT(&PyType_Type)

PyType_Type is an object declared dllimport in Python.h as it's provided
by the main python DLL.  This is one of those differences between ELF
and PE, the address of a symbol from a shared library cannot be used as
a constant initializer in PE.  The testcase boils down to this:

$ cat >tc.c <<EOF
extern __attribute__((dllimport)) int fromdll;

typedef struct { int *foo; } foo_t;

static foo_t foo = { &fromdll };
EOF

$ gcc -c tc.c
tc.c:5: error: initializer element is not constant
tc.c:5: error: (near initialization for `foo.foo')

A little googling shows that apparently you can supply 0 to this
HEAD_INIT macro and the field will be initialized with the proper value
at runtime.  Google code search shows some instances where they define a
macro for this for documentation purposes:

#define DEFERRED_ADDRESS(ADDR) 0
...
static PyTypeObject foo = {
	PyObject_HEAD_INIT(DEFERRED_ADDRESS(&PyType_Type))

So, that would probably be the first workaround I'd try for porting this
library to PE.

Brian

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