compiled C function for postgresql fails (64-bit only)

I have a function that I've used since early postgres-7.x days. Now migrating to a 64-bit
(i7) machine - running 2.6.30/'squeeze' with postgresql-8.4.1-1. This function is a simple
one that takes a string representation of a number as its sole argument (engineering
notation), and returns the number. The floating point value that it returns is the same
value {6.94822224692498e-310} with every call, even when the string changes.
The same function works perfectly on a separate 2.6.30/'squeeze' system, PG-8.4.1-1,
that is a 32-bit system - just like it has on previous postgres versions.
If I enable a diagnostic mid-functon dump-to-a-file, I can see that the function
is receiving its input and computing the output properly - it's "just" a matter of
getting the output translated into sql-land. This is with the "Version 0" calling
conventions, with a return type of float8* . Attempting "Version 1" calling conventions
on the 64-bit system has not yet been successful - I haven't yet been able to avoid a client
segfault, whether I use a stack variable for the float8 result, or use palloc().

In case it would help, the key parts of the function are:

float8 *sick_fct(const char *strng)
float8 *result;
char stack_string_buffer[BIG_STRING_SPACE];

// string copy operation : strng -> stack_string_buffer

result= (float8*)palloc(sizeof(float8));
*result= inner_conversion_function(stack_string_buffer);
// printing this *result to a file shows that the conversion is correct
// the mysteriously wrong part seems to be:
return result;

I'm compiling it as:
g++-4.3 -c -I/usr/include -I/usr/lib/gcc/x86_64-linux-gnu/4.3/include -Wall -Wshadow -Wpointer-arith -Wcast-align -I/usr/include/postgresql -I(yet more includes) -fPIC -x c sick_fct.c -o sick_fct.o

and building the library as:
g++-4.3 -shared -Wl,-soname, -o *.o

and "creating" the function within PG as:
AS '/lib-path/lib_sickfct', 'sick_fct' LANGUAGE C STRICT;

Note that changing the "float" on the last line to "double precision" changes nothing.

Odds are that I'm doing something stupid, but so far I haven't figured out
what it is. Thanks for any insights you might have!


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