#342 PIC backend: pointer passing arg smash

[Linas Vepstas]

In certain rare cases, the stack is smashed. Sorry, no simple test
case. The bug occured when

1) the virtual stack addres was set to 0x38
2) the C program was large enough to have data above 0x38
3) a void func (const char *) routine was called.

The const char * pointer was passed in W (high addres bits) and
in s0x38 (low adress bits). Unfortuantely, it was received with
a r0x38 instead of the correct s0x38. Don't know why.

Setting the virtual stack address above any real RAM on the PIC
fixes the problem.

The following patch does the trick:

Index: pcode.c

RCS file: /cvsroot/sdcc/sdcc/src/pic/pcode.c,v
retrieving revision 1.27
diff -r1.27 pcode.c
1088c1088,1096
< initStack(0x38, 8);
---
> /* Note:
> * The virtual stack is placed higher than any real memory in the PIC.
> * If it is placed in low memory, then there are certain cases (pointer
> * passing) where it gets smashed (due to a bug elsewhere??). The bug
> * I saw was during function entry with a const char * pointer, and then
> * popRegFromIdx generated an r0x reference instead of the * correct
> * s0x reference.
> */
> initStack(0x888, 8);