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);
}
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