My is the order of parameters reversed for functions that are dynamically loaded from shared C libraries?

David Nies via Digitalmars-d-learn digitalmars-d-learn at puremagic.com
Sun Nov 15 09:54:24 PST 2015


Apparantly, the order in which parameters are passed to a 
dynamically loaded C function is reversed. See the following 
minimal example:

----------------
%> cat dll.c
#include "stdio.h"

int dll2(const char* first, const char* second) {
     printf("dll2() - first: '%s', second: '%s'\n", first, second);
     return 0;
}

int dll3(const char* first, const char* second, const char* 
third) {
     printf("dll3() - first: '%s', second: '%s', third: '%s'\n",
            first,
            second,
            third);
     return 0;
}
----------------

I compiled it with the following commands:

%> gcc -c dll.c -fpic
%> gcc -shared -o libdll.dyld dll.o
%> file libdll.dyld
libdll.dyld: Mach-O 64-bit dynamically linked shared library 
x86_64

Now, I'm using it with a very simple D program and see very 
unexpected results:

----------------
%> cat main.d
import std.stdio, std.string, core.sys.posix.dlfcn;

// extern functions
alias nothrow int function(const char*, const char*) dll2_fn;
alias nothrow int function(const char*, const char*, const char*) 
dll3_fn;

void main() {
     string sdlLibPath = "libdll.dyld";
     auto libraryHandle = dlopen(sdlLibPath.toStringz(), 
RTLD_LAZY);
     scope(exit) dlclose(libraryHandle);

     dll2_fn dll2 = cast(dll2_fn)dlsym(libraryHandle, "dll2");
     dll2("one", "two");

     dll3_fn dll3 = cast(dll3_fn)dlsym(libraryHandle, "dll3");
     dll3("one", "two", "three");
}

%> rdmd main.d
dll2() - first: 'two', second: 'one'
dll3() - first: 'three', second: 'two', third: 'one'
----------------

The order in which the C functions get the parameters is exactly 
the reverse order in which I supply them in D.

What is happening there? I also tried to export a function that 
has two different types from the C library. Calling it the same 
way from the client D program causes a segfault - which I'd 
expect when the parameters are really reversed.

How can I make sure the order is correct?


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