[sdcc-devel] [ sdcc-Bugs-840381 ] bad pointer difference computing and one sigsegv as bonus

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Bugs item #840381, was opened at 2003-11-12 01:09
Message generated for change (Tracker Item Submitted) made by Item Submitter
You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=100599&aid=840381&group_id=599

Category: None
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: Josef Pavlik (jetset)
Assigned to: Nobody/Anonymous (nobody)
Summary: bad pointer difference computing and one sigsegv as bonus

Initial Comment:
Hi guys,
I found that the computing pointer difference  in the following 
example is  incorrect . The result is divided by two, but either FLASH 
array and fp pointer are pointers to unsigned char.

Creating this simple example I found a nice SIGSEGV :-)
Try uncomment the define :-)
The sigsegv can be verified only with --model-small. With 
--model-large the linker reports undefined variable, that is not too 
clear to understand. Uninitialized variable warning can be better, if 
possible.

sdcc -v
SDCC : 
mcs51/gbz80/z80/avr/ds390/pic14/pic16/TININative/xa51/ds400/hc
08 2.3.6 (Nov 11 2003) (UNIX)

------------------------------------------------------------------
//#define I_WANT_SEE_A_NICE_SIGSEGV // with --model-small
xdata unsigned char FLASH[0x6000];         
	
int main()
{
  unsigned int l, l2;
  xdata unsigned char *fp;

#ifndef I_WANT_SEE_A_NICE_SIGSEGV   
  fp=&FLASH[0x4000];
#endif  
  l=&FLASH[0x6000]-fp; // this line is compiled incorrectly
  l2=(unsigned int)&FLASH[0x6000]-(unsigned int)fp; // this is ok
  return l+l2;
}

/* incorrect result:
	
;bug_array1.c:9: fp=&FLASH[0x4000];
;bug_array1.c:10: l=&FLASH[0x6000]-fp;
;     genMinus
        mov     a,#(_FLASH + 0x6000)
        clr     c
        subb    a,#(_FLASH + 0x4000)
        mov     r2,a
        mov     a,#((_FLASH + 0x6000) >> 8)
        subb    a,#((_FLASH + 0x4000) >> 8)
        mov     r3,a
;     genAssign
        clr     a
        mov     (__divsint_PARM_2 + 1),a
        mov     __divsint_PARM_2,#0x02
;     genCall
        mov     dpl,r2
        mov     dph,r3
        lcall   __divsint
        mov     r2,dpl
        mov     r3,dph

*/		



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