16-bit C compiler generate wrong code for direct call to absolute address (constant)

[jmalak]

It was reported by @sqpat on Discord server.

Below is sample code which exhibit a issue

typedef short __far fx(unsigned char);

fx *funcloc  = (fx *)0x6EA90034L;

int t1( void )
{
    short p1;
    short p2;
    p1 = (funcloc)(2);
    p2 = ((fx *)0x6EA90034L)(2);
    return( p1 + p2 );
}

and disassembled code

GROUP: 'DGROUP' CONST,CONST2,_DATA

Segment: _TEXT BYTE USE16 00000013 bytes
0000                            t1_:
0000  52                                push            dx
0001  B8 02 00                          mov             ax,0x0002
0004  FF 1E 00 00                       call            dword ptr _funcloc
0008  89 C2                             mov             dx,ax
000A  B8 02 00                          mov             ax,0x0002
000D  FF 10                             call            word ptr [bx+si]             ; <<-- wrong generated code
000F  01 D0                             add             ax,dx
0011  5A                                pop             dx
0012  C3                                ret

Routine Size: 19 bytes,    Routine Base: _TEXT + 0000

No disassembly errors

Segment: CONST WORD USE16 00000000 bytes

Segment: CONST2 WORD USE16 00000000 bytes

Segment: _DATA WORD USE16 00000004 bytes
0000                            _funcloc:
0000  34 00 A9 6E                                     4..n

It looks like it is code generator bug and it is related to absolute address (constant) for call. I checked it with far address operator (0x6EA9 :> 0x0034) which create far pointer explicitly with same result. For now it is necessary assign such address to variable, you cannot use directly constant address for call, only for initialization.