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 <mailto:[email protected]> 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 <mailto:[email protected]> 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 <mailto:[email protected]> To: MSP430 GCC <mailto:[email protected]> 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. ____ This communication contains information which is confidential and the copyright of Nautronix. If you are not the intended recipient of this communication please delete and destroy all copies and advise Nautronix immediately. If you are the intended recipient of this communication you should not copy, disclose or distribute this communication without the prior authority of Nautronix. Any views expressed in this Communication are those of the individual sender, except where the sender specifically states them to be the views of Nautronix. Except as required at law, Nautronix does not represent, warrant and/or guarantee that the integrity of this communication has been maintained nor that the communication is free of errors, virus, interception or interference.
