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From: Felix Krause <fordprefect86@googlemail.com>
Newsgroups: comp.lang.ada
Subject: Re: StdCall and pragma Import_Function
Date: Fri, 19 Aug 2011 12:23:49 -0700 (PDT)
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Date: 2011-08-19T12:23:49-07:00
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>From the header file:

extern CL_API_ENTRY cl_int CL_API_CALL
clGetDeviceIDs(cl_platform_id   /* platform */,
               cl_device_type   /* device_type */,
               cl_uint          /* num_entries */,
               cl_device_id *   /* devices */,
               cl_uint *        /* num_devices */) CL_API_SUFFIX__VERSION_1_0;

Those macros are defined as:

#if defined(_WIN32) || defined(__CYGWIN__)
#define CL_API_ENTRY
#define CL_API_CALL __stdcall
    #define CL_CALLBACK     __stdcall
#else
#define CL_API_ENTRY
#define CL_API_CALL
    #define CL_CALLBACK
#endif

So it indeed uses StdCall convention. The corresponding output of dumpbin is:

  Version      : 0
  Machine      : 14C (x86)
  TimeDateStamp: 4E03B987 Fri Jun 24 00:09:11 2011
  SizeOfData   : 0000001E
  DLL name     : OpenCL.dll
  Symbol name  : _clGetDeviceIDs@24
  Type         : code
  Name type    : undecorate
  Hint         : 44
  Name         : clGetDeviceIDs

(I don't have a def file, but this shows the fully qualified name too.)

cl_device_type is the bitvector from my example, and GNAT searches for "clGetDeviceIDs@20".