nortond@mosys.UUCP (Daniel A. Norton) (12/22/87)
Copyright (c) 1987, Daniel A. Norton. All Rights Reserved.
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PRODUCT:
MSC 5.0 OPTIMIZING COMPILER
SYMPTOMS:
Use of intrinsic function strlen() in large data model
(/AH, /AL or /AC) results in data loss. If the intrinsic
function strlen() is called to return the length of a
string represented by an auto-storage or static-storage
pointer, and the result is returned into an external or
public variable, incorrect code is generated, resulting
in loss of data.
The error does not appear in the small or medium model.
The error does not appear if the variable holding the
returned value is in static or auto storage. The error
does not appear if the string is a static array (as
opposed to a static pointer). The error does not appear
if the string is an external or public array or is is
accessed through an external or public pointer.
WORKAROUND:
In source code which has the described characteristics,
insert the line:
#pragma function(strlen)
This statement suppresses the intrinsic and forces the
library function _strlen to be invoked instead.
REPRODUCING THE PROBLEM:
EXAMPLE SOURCE:
#include <string.h>
extern int extvar;
void dummyproc(arg)
char *arg;
{
extvar = strlen(arg);
}
COMPILER INVOCATION:
cl -c -AL -Oi -Fa bug2.c
ASSEMBLY OUTPUT:
; Static Name Aliases
;
TITLE bug2.c
NAME bug2
.8087
BUG2_TEXT SEGMENT WORD PUBLIC 'CODE'
BUG2_TEXT ENDS
_DATA SEGMENT WORD PUBLIC 'DATA'
_DATA ENDS
CONST SEGMENT WORD PUBLIC 'CONST'
CONST ENDS
_BSS SEGMENT WORD PUBLIC 'BSS'
_BSS ENDS
DGROUP GROUP CONST, _BSS, _DATA
ASSUME CS: BUG2_TEXT, DS: DGROUP, SS: DGROUP
EXTRN __acrtused:ABS
EXTRN __chkstk:FAR
COMM FAR _extvar: BYTE: 2
CONST SEGMENT
$T20001 DW SEG _extvar
CONST ENDS
BUG2_TEXT SEGMENT
ASSUME CS: BUG2_TEXT
; Line 6
PUBLIC _dummyproc
_dummyproc PROC FAR
push bp
mov bp,sp
xor ax,ax
call FAR PTR __chkstk
push di
; Line 7
; arg = 6
; Line 8
mov es,$T20001 ; *** DISCARDED
les di,DWORD PTR [bp+6] ;arg
mov cx,-1
xor ax,ax
repnz scasb
not cx
dec cx
mov WORD PTR es:_extvar,cx ; *** INVALID
; Line 9
pop di
pop bp
ret
_dummyproc ENDP
BUG2_TEXT ENDS
END
--
Daniel A. Norton nortond@mosys.UUCP
c/o Momentum Systems Corporation ...uunet!mosys!nortond
2 Keystone Avenue
Cherry Hill, NJ 08003 609/424-0734swh@hpsmtc1.HP.COM (Steve Harrold) (12/23/87)
Re: Copyright on bug report A copyright???!!! Is this a joke?? If so please explain what's so funny. --------------------- Steve Harrold ...hplabs!hpsmtc1!swh HPG200/13 (408) 447-5580 ---------------------
robf2@pyuxf.UUCP (robert fair) (12/23/87)
In article <211@mosys.UUCP>, nortond@mosys.UUCP (Daniel A. Norton) writes: > Copyright (c) 1987, Daniel A. Norton. All Rights Reserved. decribes a bug in the intrinsic strlen() for MSC 5.0 using large model. Every intrinsic I have tried (strlen,strcpy,strncpy,memcpy...) has the same bug in large model (-AL -AH, -AC). Since these tend to produce horrible, subtle problems in the code I would suggest avoid using intrinsic functions *at all* in large model [Speaking from a very frustrating weekend tracking down such `bugs'] and once again flame Microsoft for sending out a product which must be almost totally untested ! The loop optimization is also very buggy in large model, producing `hidden' bad code in inappropriate places. In short, the `optimizing' compiler really is: "An optimizing compiler for small & medium models and a joke for large model" A very pissed off MSC 5.0 user (and I LIKED MSC 3.0 & 4.0...) Rob Fair Currently at: Bellcore/CHC ihnp4!pyuxww!pyuxf!robf2