Will this work?
struct x{ /* struct of type x defined */
int a,b,c,d;
};
struct x *v[2]; /* array of 2 pointers to structures of type x -
somewhere initialized, OK ?*/
/* swap pointers, this means after call to swap(), v[0] holds the
pointer to v[1] and viceversa */
void swap(void) {
struct x *tmp; /* this declaraction should be struct x *tmp , and
not the variable tmp of type struct x !!! */
*tmp = *v[0];
*v[0]= *v[1];
*v[1]= *tmp;
}
Garst
>
Luke Hoffmann wrote:
>
> Sorry, I'll repost this with HTML off ;-)
>
> Hi,
>
> I think Oleg has identified a real problem.
> Lets leave the question of "is this the best way to do it" aside and realise
> that "this is the best way to reproduce the problem"!
>
> The swap() function is not swapping pointers it is swapping the contents of
> structures.
> This is a valid operation and it produces some interesting code!
> Clearly the code attached is wrong.
>
> Regards
> Luke
>
>
> -----Original Message-----
> From: Roberto G. Berner [mailto:[email protected]]
> Sent: Thursday, 23 January 2003 4:36 AM
> To: [email protected]
> Subject: RE: [Mspgcc-users] Struct assignment BUG...
>
> Dear Oleg:
>
> Accept my apologies, but I think you should check this. If I am wrong, please
> excuse me.
>
>
> struct x{ /* struct of type x defined */
> int a,b,c,d;
> };
>
> struct x *v[2]; /* array of 2 pointers to structures of type x - somewhere
> initialized, OK ?*/
>
> /* swap pointers, this means after call to swap(), v[0] holds the pointer to
> v[1] and viceversa */
> void swap(void) {
> struct x tmp; /* this declaraction should be struct x *tmp , and not the
> variable tmp of type struct x !!! */
> tmp=*v[0]; /* tmp should be a pointer in order to hold pointers
> properly */
> *v[0]=*v[1];
> *v[1]=tmp;
> }
>
> Kind regards,
>
> Roberto G. Berner
> [email protected]
> [email protected]
> 4308 3500 tel
> 4308 3700 fax
> 15 5122 6095 cel
> ----- Original Message -----
> From: Oleg Skydan
> To: [email protected]
> Sent: Wednesday, January 22, 2003 4:27 PM
> Subject: Re: [Mspgcc-users] Struct assignment BUG...
>
> Dear Roberto,
>
> The swap function exchanges the contents of the two structs,
> pointed by elements of the array v, so there a significant BUG.
>
> I have omitted the initialization section for simplicity (I have found this
> BUG in
> a real program, which is very large).
>
> Anyway the stack pointer should point to the same location at the function
> exit and entry (unless it is explicitly changed, using asm statement for
> example).
>
> Thanks,
> Oleg.
> ----- Original Message -----
> From: Roberto G. Berner
> To: [email protected]
> Sent: Wednesday, January 22, 2003 6:25 PM
> Subject: RE: [Mspgcc-users] Struct assignment BUG...
>
> Dear Oleg:
>
> I think that there is no bug. Should I suggest trying ...
>
> struct x *tmp;
>
> Kind regards,
>
> Roberto G. Berner
> [email protected]
> [email protected]
> 4308 3500 tel
> 4308 3700 fax
> 15 5122 6095 cel
> ----- Original Message -----
> From: Oleg Skydan
> To: MSP430 GCC
> Sent: Wednesday, January 22, 2003 12:12 PM
> Subject: [Mspgcc-users] Struct assignment BUG...
>
> Hello, All !
>
> I found a significant BUG when using struct assignment.
>
> Here is the sample:
>
> struct x{
> int a,b,c,d;
> };
>
> struct x *v[2];
>
> void swap(void)
> {
> struct x tmp;
> tmp=*v[0];
> *v[0]=*v[1];
> *v[1]=tmp;
> }
>
> And here is GCC's listing (with -O option):
>
> /***********************
> * Function `swap'
> ***********************/
> swap:
> /* prologue: frame size = 8 */
> .L__FrameSize_swap=0x8
> .L__FrameOffset_swap=0x8
> sub #8, r1 ; 8, fpn 0
> /* prologue end (size=1) */
> mov &v, r15
> mov @r15+, @r1
> mov @r15+, 2(r1)
> mov @r15+, 4(r1)
> mov @r15+, 6(r1)
> mov &v+2, r14
> mov @r14+, 0(r15)
> mov @r14+, 2(r15)
> mov @r14+, 4(r15)
> mov @r14+, 6(r15)
> mov &v+2, r15
> mov @r1+, 0(r15) ;We should not change the stack pointer here !
> mov @r1+, 2(r15)
> mov @r1+, 4(r15)
> mov @r1+, 6(r15)
> /* epilogue: frame size=8 */
> add #8, r1 ;After this command the stack pointer points
> to the illegal location !
> ret
> /* epilogue end (size=2) */
> /* function swap size 33 (30) */
>
> I use win32 version (from 10.12.2002).
> Thanks, Oleg.
>
>
>
