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Compiler Pragmas and Inline Stubs

Overview

AmigaOS library calls use register-based calling conventions (arguments in D0–D7/A0–A6). C compilers need pragmas or inline stubs to generate the correct register assignments instead of stack-based calls.

Three Mechanisms

Method	Compiler	How it works
Pragmas	SAS/C	`#pragma libcall` directive
Inline headers	GCC	Inline asm functions in `<inline/lib.h>`
Proto headers	All	`<proto/lib.h>` — auto-selects pragma or inline

Pragma Example (SAS/C)

#pragma libcall DOSBase Open 1e 2102
/* Translates to: LVO = -0x1E = -30
   Args: D1 = arg1 (name), D2 = arg2 (mode)
   Result: D0 */

Inline Example (GCC)

/* inline/exec.h */
static __inline APTR
AllocMem(ULONG byteSize, ULONG requirements)
{
    register APTR _res __asm("d0");
    register ULONG _byteSize __asm("d0") = byteSize;
    register ULONG _requirements __asm("d1") = requirements;
    register struct ExecBase *_SysBase __asm("a6") = SysBase;
    __asm volatile (
        "jsr -198(%%a6)"
        : "=r"(_res)
        : "r"(_byteSize), "r"(_requirements), "r"(_SysBase)
        : "d1","a0","a1","cc","memory"
    );
    return _res;
}

Generating Pragmas/Inlines from FD Files

# fd2pragma (Aminet: dev/misc/fd2pragma.lha):
fd2pragma exec_lib.fd exec_lib.sfd TO pragmas/exec_pragmas.h SPECIAL 6
fd2pragma exec_lib.fd exec_lib.sfd TO inline/exec.h SPECIAL 70

Proto Headers

/* proto/exec.h — portable wrapper: */
#ifdef __SASC
#include <pragmas/exec_pragmas.h>
#elif defined(__GNUC__)
#include <inline/exec.h>
#endif

extern struct ExecBase *SysBase;

References

NDK39: pragmas/, inline/, proto/ directories
fd_files.md — FD file format

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