[Sdcc-user] cast to (void *) differs from cast to (u8_t *)

[Anthony A. <ant...@gm...>]

Hello SDCC-users,

   While working on the contiki OS, I found a strange behavior in SDCC.  
I noticed when a variable was cast as (void *) the generated code 
differed than if cast as (u8_t*).

Here is the example demonstrating the issue:



memset((*void **)(&nd6_opt_llao->addr) + UIP_LLADDR_LEN, 0, 
UIP_ND6_OPT_LLAO_LEN - 2 - UIP_LLADDR_LEN);

vs

memset((*u8_t **)(&nd6_opt_llao->addr) + UIP_LLADDR_LEN, 0, 
UIP_ND6_OPT_LLAO_LEN - 2 - UIP_LLADDR_LEN);





                            1600 ;       
../../core/net/uip-nd6-io.c:344: memset((void *)(&nd6_opt_llao->addr) + 
UIP_LLADDR_LEN, 0, UIP_ND6_OPT_LLAO_LEN - 2 - UIP_LLADDR_LEN);

The problem/differences comes at 1610 when indexing into nd6_opt_llao to 
reach addr.  In the (void *) version 0x02 is added, ignoring the 
addition of UIP_LLADDR_LEN.

    05A9 90s00r01           1601         mov     dptr,#_nd6_opt_llao
    05AC E0                 1602         movx    a,@dptr
    05AD FA                 1603         mov     r2,a
    05AE A3                 1604         inc     dptr
    05AF E0                 1605         movx    a,@dptr
    05B0 FB                 1606         mov     r3,a
    05B1 A3                 1607         inc     dptr
    05B2 E0                 1608         movx    a,@dptr
    05B3 FC                 1609         mov     r4,a
    05B4 74 02              1610         mov     a,#0x02
    05B6 2A                 1611         add     a,r2
    05B7 FA                 1612         mov     r2,a
    05B8 E4                 1613         clr     a
    05B9 3B                 1614         addc    a,r3
    05BA FB                 1615         mov     r3,a
    05BB 74 06              1616         mov     a,#0x06
    05BD C0 E0              1617         push    acc
    05BF E4                 1618         clr     a
    05C0 C0 E0              1619         push    acc
    05C2 E4                 1620         clr     a
    05C3 C0 E0              1621         push    acc
    05C5 8A 82              1622         mov     dpl,r2
    05C7 8B 83              1623         mov     dph,r3
    05C9 8C F0              1624         mov     b,r4
    05CB 12s00r00           1625         lcall   _memset

In the (u8_t *) version the correct offset for addr of 10 is used:

                            1600 ;       
../../core/net/uip-nd6-io.c:344: memset((void *)(&nd6_opt_llao->addr) + 
UIP_LLADDR_LEN, 0, UIP_ND6_OPT_LLAO_LEN - 2 - UIP_LLADDR_LEN);
    05A9 90s00r01           1601         mov     dptr,#_nd6_opt_llao
    05AC E0                 1602         movx    a,@dptr
    05AD FA                 1603         mov     r2,a
    05AE A3                 1604         inc     dptr
    05AF E0                 1605         movx    a,@dptr
    05B0 FB                 1606         mov     r3,a
    05B1 A3                 1607         inc     dptr
    05B2 E0                 1608         movx    a,@dptr
    05B3 FC                 1609         mov     r4,a
    05B4 74 0A              1610         mov     a,#0x0A
    05B6 2A                 1611         add     a,r2
    05B7 FA                 1612         mov     r2,a
    05B8 E4                 1613         clr     a
    05B9 3B                 1614         addc    a,r3
    05BA FB                 1615         mov     r3,a
    05BB 74 06              1616         mov     a,#0x06
    05BD C0 E0              1617         push    acc
    05BF E4                 1618         clr     a
    05C0 C0 E0              1619         push    acc
    05C2 E4                 1620         clr     a
    05C3 C0 E0              1621         push    acc
    05C5 8A 82              1622         mov     dpl,r2
    05C7 8B 83              1623         mov     dph,r3
    05C9 8C F0              1624         mov     b,r4
    05CB 12s00r00           1625         lcall   _memset



I submitted a bug tracker report with the following example program:

#include <string.h>
#define UIP_LLADDR_LEN 8

struct uip_802154_longaddr {
   unsigned char addr[8];
};
typedef struct uip_802154_longaddr uip_lladdr_t;

struct uip_nd6_opt_llao {
   unsigned char type;
   unsigned char len;
   uip_lladdr_t addr;
};

static struct uip_nd6_opt_llao *nd6_opt_llao;


void main (void)
{
   unsigned char buf[300];
   nd6_opt_llao = (struct uip_nd6_opt_llao *)buf;
   memset((unsigned char *)(&nd6_opt_llao->addr) + UIP_LLADDR_LEN, 0, 6);
}