gnupic: Re: Segmentation fault ... other locations of problem and different types of fixes
Subject:
Re: Segmentation fault ... other locations of problem and different types of fixes
From:
####@####.#### (Linas Vepstas)
Date:
30 May 2002 22:18:55 -0000
Message-Id: <20020530220840.GB8318@backlot.linas.org>
A few weeks ago, when I said that SDCC was usable by "the adeventerous",
if they didn't miond working around odd bugs ... below is exactly what
I meant.
These types of bugs aren't acceptable for a production compiler used
by beginning programmers, but its very typical of new system bringup.
(Its even more fun when your cpu chip is brand new too, and hasn't been
debugged yet either).
--linas
On Wed, May 29, 2002 at 05:54:58PM -0400, Robert Warner was heard to remark:
> This may or may not help. There were 2 additional locations. However each
> required a different type of fix to solve it. Here they are
> (btw, I do this at night ... so I don't get your mails 'til the next day)
> Not to lecture (please do not take offense) ... from my days of teaching
> ANSI/ISO C for embedded systems ... variables whether initaialized or not can
> be used as indices for arrays. C does not check bounds on array access.
> (Unlike Ada).
>
>
> Example of problem #2
> //BOOL get_hexbyte(BYTE *val)
> BOOL get_hexbyte( BYTE *val, int *prxout)
> {
> BYTE b;
> BOOL ok=0;
>
> *val = 0;
> // while (isxdigit(rxbuff[rxout]) && get_byte(&b)) //Segmentation Fault
> // while (isxdigit(rxbuff[*prxout]) && get_byte(&b)) //no help
> //Fixed with pointer arithmatic
> while ( isxdigit( *((BYTE *)(rxbuff) + *prxout)) && get_byte(&b))
> {
> ok = 1;
> *val <<= 4;
> if (b <= '9')
> *val += b - '0';
> else
> *val += (b-'A'+10) & 0xf;
> }
> return(ok);
> }
>
> Example of problem #3
> //BYTE getch_slip(void)
> BYTE getch_slip( int *prxout)
> {
> BYTE b=0;
>
> slipend = rxout>=rxcount;
> if (!slipend)
> {
> // b = rxbuff[rxout++]; //Segmentation Fault
> b = *(((BYTE *)rxbuff) + *prxout++); //Fixed with pointer arithmatic
> *prxout++;
> check_byte(b);
> }
> return(b);
> }
>
>
> Hopefully this additional information helps
> Thanks
> Bob
>
>
>
> On Wednesday 29 May 2002 09:30, Scott Dattalo wrote:
> > On Tue, 28 May 2002, Robert Warner wrote:
> > > Ok, after several compile/edit sequences I've come up with the
> > > following. It appears an array indexed with a variable causes a problem.
> >
> > And this is undoubtedly a bug in SDCC. I'll look into this right now...
> >
> > Thanks for the report,
> > Scott
> >
> >
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