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struct NODE{ struct NODE Succ; struct NODE Prev; }; struct LIST{ struct NODE *Head; struct NODE *Tail; int count; }; struct LIST *List; struct NODE *N; ...... for(N = List->Head;N;N = N->Succ) { ...... }
I tried two different settings (using optimization level 0 and 8)under Large Memory Model,When using level 8,N and List were located in the same memory address,but when level 0,they weren't. Level 8:
SYMBOL TABLE OF MODULE: test (MAIN) VALUE REP CLASS TYPE SYMBOL NAME ==================================================== --- MODULE --- --- MAIN 0200000EH PUBLIC XDATA --- SecondNode 02000006H PUBLIC XDATA --- MyList 02000000H PUBLIC XDATA --- FirstNode 01000003H PUBLIC CODE --- main 01000003H BLOCK CODE --- LVL=0 00000001H SYMBOL DATA --- List 00000001H SYMBOL DATA --- N --- BLOCKEND --- --- LVL=0
SYMBOL TABLE OF MODULE: test (MAIN) VALUE REP CLASS TYPE SYMBOL NAME ==================================================== --- MODULE --- --- MAIN 0200000EH PUBLIC XDATA --- SecondNode 02000006H PUBLIC XDATA --- MyList 02000000H PUBLIC XDATA --- FirstNode 01000003H PUBLIC CODE --- main 01000003H BLOCK CODE --- LVL=0 02000014H SYMBOL XDATA --- List 02000017H SYMBOL XDATA --- N --- BLOCKEND --- --- LVL=0
Ok, I stripped down the code: optimization level 8, large (code/data), generic 8051 device
struct NODE{ struct NODE *Succ; struct NODE *Prev; }; struct LIST{ struct NODE *Head; struct NODE *Tail; int count; }; main() { struct LIST *List; struct NODE *N; // loop over all nodes for(N = List->Head;N;N = N->Succ) { } }
VALUE REP CLASS TYPE SYMBOL NAME ==================================================== --- MODULE --- --- MAIN 0100004AH PUBLIC CODE --- main 0100004AH BLOCK CODE --- LVL=0 0100004AH BLOCK CODE NEAR LAB LVL=1 02000000H SYMBOL XDATA --- List 00000001H SYMBOL DATA --- N --- BLOCKEND --- --- LVL=1 --- BLOCKEND --- --- LVL=0
I'm baffled as to why "List" seems to be being placed in xdata in your map file. If I compile this code in the small memory model, all variables are placed in DATA. List and N are placed at the same address, however I think this is because N is never used in the code hence it doesn't matter where it is placed: struct NODE{ struct NODE *Succ; struct NODE *Prev; }; struct LIST{ struct NODE *Head; struct NODE *Tail; int count; }; struct LIST MyList; struct NODE FirstNode; struct NODE SecondNode; main() { struct LIST *List; struct NODE *N; // init nodes and list FirstNode.Succ = &SecondNode; FirstNode.Prev = 0; SecondNode.Succ = 0; SecondNode.Prev = &FirstNode; MyList.Head = &FirstNode; MyList.Tail = &SecondNode; MyList.count = 2; List = &MyList; // loop over all nodes for(N = List->Head;N;N = N->Succ) { } } VALUE REP CLASS TYPE SYMBOL NAME ==================================================== --- MODULE --- --- JUNK 00000016H PUBLIC DATA --- SecondNode 00000010H PUBLIC DATA --- FirstNode 00000008H PUBLIC DATA --- MyList 01000003H PUBLIC CODE --- main 01000003H BLOCK CODE --- LVL=0 00000001H SYMBOL DATA --- List 00000001H SYMBOL DATA --- N 01000003H LINE CODE --- #44 01000003H LINE CODE --- #45 01000003H LINE CODE --- #50 0100000CH LINE CODE --- #51 01000015H LINE CODE --- #52 0100001EH LINE CODE --- #53 01000027H LINE CODE --- #54 01000030H LINE CODE --- #55 01000039H LINE CODE --- #56 0100003FH LINE CODE --- #58 01000045H LINE CODE --- #61 0100004BH LINE CODE --- #62 0100004BH LINE CODE --- #63 0100004FH LINE CODE --- #65 --- BLOCKEND --- --- LVL=0 However, if I initialise N: struct NODE{ struct NODE *Succ; struct NODE *Prev; }; struct LIST{ struct NODE *Head; struct NODE *Tail; int count; }; struct LIST MyList; struct NODE FirstNode; struct NODE SecondNode; main() { struct LIST *List; struct NODE *N; // init nodes and list FirstNode.Succ = &SecondNode; FirstNode.Prev = 0; SecondNode.Succ = 0; SecondNode.Prev = &FirstNode; MyList.Head = &FirstNode; MyList.Tail = &SecondNode; MyList.count = 2; List = &MyList; N=&FirstNode; // loop over all nodes for(N = List->Head;N;N = N->Succ) { } } VALUE REP CLASS TYPE SYMBOL NAME ==================================================== --- MODULE --- --- JUNK 00000016H PUBLIC DATA --- SecondNode 00000010H PUBLIC DATA --- FirstNode 00000008H PUBLIC DATA --- MyList 01000003H PUBLIC CODE --- main 01000003H BLOCK CODE --- LVL=0 0000001CH SYMBOL DATA --- List 00000001H SYMBOL DATA --- N 01000003H LINE CODE --- #44 01000003H LINE CODE --- #45 01000003H LINE CODE --- #50 0100000CH LINE CODE --- #51 01000015H LINE CODE --- #52 0100001EH LINE CODE --- #53 01000027H LINE CODE --- #54 01000030H LINE CODE --- #55 01000039H LINE CODE --- #56 0100003FH LINE CODE --- #58 01000048H LINE CODE --- #59 01000048H LINE CODE --- #61 01000054H LINE CODE --- #62 01000054H LINE CODE --- #63 01000058H LINE CODE --- #65 --- BLOCKEND --- --- LVL=0 Stefan
List is placed in XDATA because I use the large memory model (see message)... "N is never used in the code hence it doesn't matter where it is placed: " N is used in code: "N = List->Head" and "N = N->Succ" in the for-loop. In small model I get the following map-file:
VALUE REP CLASS TYPE SYMBOL NAME ==================================================== --- MODULE --- --- MAIN 01000003H PUBLIC CODE --- main 01000003H BLOCK CODE --- LVL=0 01000003H BLOCK CODE NEAR LAB LVL=1 00000008H SYMBOL DATA --- List 00000001H SYMBOL DATA --- N --- BLOCKEND --- --- LVL=1 --- BLOCKEND --- --- LVL=0
"List is placed in XDATA because I use the large memory model" Ok, but shouldn't N therefore be placed in xdata as well? Quoting from your map file above: 02000000H SYMBOL XDATA --- List 00000001H SYMBOL DATA --- N "N is used in code: "N = List->Head" and "N = N->Succ" in the for-loop" Yes, I must have been sleeping. Again. I think Hans is right, the optimisation is legitimately causing this. The order of events is (pseudocode): List=An address; N=List->Head; LABEL: N=N->Succ; if(N) goto LABEL So, List and N can occupy the same location without anything going wrong. Stefan