[sdcc-devel] [ sdcc-Bugs-3604563 ] [MCS51] Certain variables overlap in the XRAM

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Bugs item #3604563, was opened at 2013-02-13 11:14
Message generated for change (Tracker Item Submitted) made by molnarkaroly
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Category: None
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Molnár Károly (molnarkaroly)
Assigned to: Nobody/Anonymous (nobody)
Summary: [MCS51] Certain variables overlap in the XRAM

Initial Comment:
Example:

__xdata __at (0x0000) unsigned char bf0[256];
__xdata unsigned char var0;
__xdata unsigned char var1;
__xdata unsigned char var2;
__xdata unsigned char var3;

void main(void)
{
  bf0[0] = '0';
  var0   = '1';
  var1   = '2';
  var2   = '3';
  var3   = '4';
}

Excerpt from the disassembled list (mcs51-disasm.pl):

_main:

0x0064: 90 00 00	mov	DPTR, #0x0000				; DPTR = 0x0000
0x0067: 74 30		mov	A, #0x30				; ACC = 0x30 {'0'}
0x0069: F0		movx	@DPTR, A				; XRAM[DPTR] = ACC
0x006A: 90 00 00	mov	DPTR, #0x0000				; DPTR = 0x0000
0x006D: 74 31		mov	A, #0x31				; ACC = 0x31 {'1'}
0x006F: F0		movx	@DPTR, A				; XRAM[DPTR] = ACC
0x0070: 90 00 01	mov	DPTR, #0x0001				; DPTR = 0x0001
0x0073: 74 32		mov	A, #0x32				; ACC = 0x32 {'2'}
0x0075: F0		movx	@DPTR, A				; XRAM[DPTR] = ACC
0x0076: 90 00 02	mov	DPTR, #0x0002				; DPTR = 0x0002
0x0079: 74 33		mov	A, #0x33				; ACC = 0x33 {'3'}
0x007B: F0		movx	@DPTR, A				; XRAM[DPTR] = ACC
0x007C: 90 00 03	mov	DPTR, #0x0003				; DPTR = 0x0003
0x007F: 74 34		mov	A, #0x34				; ACC = 0x34 {'4'}
0x0081: F0		movx	@DPTR, A				; XRAM[DPTR] = ACC
0x0082: 22		ret						; PCH = [SP--], PCL = [SP--]


I have included a simple example program.

SDCC : mcs51/gbz80/z80/z180/r2k/r3ka/ds390/pic16/pic14/TININative/ds400/hc08/s08 3.2.1 #8384 (Jan 13 2013) (Linux)

Károly

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