From: Rob Pike <robpike@gmail.com>
To: John Cowan <cowan@ccil.org>
Cc: The Eunuchs Hysterical Society <tuhs@tuhs.org>
Subject: Re: [TUHS] reviving a bit of WWB
Date: Tue, 22 Sep 2020 07:22:08 +1000 [thread overview]
Message-ID: <CAKzdPgwD2s9SbKQgRa46S_kVCVXC7-_bqEn9UMHGb9Zve1=x2g@mail.gmail.com> (raw)
In-Reply-To: <CAD2gp_T=RjQkrFeaeu-e4b4qvQFa-uZWTgg6mBiOJhF5fJh9qw@mail.gmail.com>
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Back when we were running v5 at the University of Toronto, we had a
graphics device that we accessed, on our split I&D space 11/45, using 0,
something like this:
struct x {
int reg0, reg1, ...;
};
0->reg1 = 0234;
Several old details of old C made this possible as well: Struct tags were
global, -> worked on any pointer, and ints and pointers were
interchangeable.
-rob
On Tue, Sep 22, 2020 at 6:51 AM John Cowan <cowan@ccil.org> wrote:
>
>
> On Mon, Sep 21, 2020 at 1:55 AM Steve Nickolas <usotsuki@buric.co> wrote:
>
>
>> I've never written anything that uses varargs, so I've never run into
>> that. But I've actually done quite a bit of work with an environment
>> where this isn't true: MS-DOS using the large or huge model. In this
>> environment, sizeof(int)=2, and sizeof(void*) is 4. Of course, it's not
>> conformant to pass an int variable as an argument where a pointer variable
>> is expected.
>>
>
> If the compiler was ISO-conformant (which it almost certainly was not),
> that would not matter. 0 in int context would be a 2-byte int with all
> bits zero, and 0 in pointer context would be a 4-byte null pointer,
> probably with all bits zero.
>
> C doesn't require that the address represented by the null pointer
> (whether or not it is all-bits-zero) is inaccessible, merely that there is
> no C object or function there. A simple shim of the appropriate size (1,
> 2, 4, 8 bytes depending on the CPU's alignment rules) will suffice.
>
>
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next prev parent reply other threads:[~2020-09-21 21:23 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-20 23:00 Norman Wilson
2020-09-20 23:53 ` Clem Cole
2020-09-21 0:00 ` Clem Cole
2020-09-21 2:24 ` John Cowan
2020-09-21 0:09 ` Warner Losh
2020-09-21 1:05 ` Clem Cole
2020-09-21 5:55 ` Steve Nickolas
2020-09-21 5:59 ` Warner Losh
2020-09-21 18:40 ` Paul Winalski
2020-09-21 19:56 ` Dan Cross
2020-09-21 20:50 ` John Cowan
2020-09-21 21:22 ` Rob Pike [this message]
2020-09-21 21:57 ` Clem Cole
2020-09-21 23:56 ` John Cowan
2020-09-22 0:54 ` Richard Salz
2020-09-21 21:39 ` Steve Nickolas
-- strict thread matches above, loose matches on Subject: below --
2020-09-25 14:19 Doug McIlroy
2020-09-28 17:35 ` Angelo Papenhoff
2020-09-20 22:51 Norman Wilson
2020-09-19 1:51 Doug McIlroy
2020-09-20 18:42 ` arnold
2020-09-20 19:28 ` Will Senn
2020-09-20 20:12 ` Steve Nickolas
2020-09-20 20:26 ` Doug McIlroy
2020-09-20 20:57 ` Doug McIlroy
2020-09-20 22:13 ` Clem Cole
2020-09-21 20:43 ` Steffen Nurpmeso
2020-09-20 20:58 ` Steve Nickolas
2020-09-20 21:33 ` Brantley Coile
2020-10-07 5:43 ` scj
2020-09-20 21:35 ` John Cowan
2021-02-02 23:08 ` Greg A. Woods
2021-02-02 23:47 ` Larry McVoy
2021-02-03 0:11 ` Dave Horsfall
2021-02-03 0:19 ` Larry McVoy
2021-02-03 2:04 ` Richard Salz
2021-02-03 3:32 ` Dave Horsfall
2021-02-03 4:32 ` M Douglas McIlroy
2021-02-03 11:27 ` Peter Jeremy via TUHS
2021-02-03 20:09 ` Dave Horsfall
2021-02-03 20:13 ` Niklas Karlsson
2021-02-03 23:46 ` Tom Lyon
2021-02-03 22:19 ` Dave Horsfall
2021-02-03 22:55 ` M Douglas McIlroy
2020-09-20 22:15 ` Clem Cole
2020-09-20 22:47 ` John Cowan
2020-09-21 20:48 ` Steffen Nurpmeso
2020-09-21 20:46 ` Steffen Nurpmeso
2020-09-24 2:25 ` Dave Horsfall
2020-09-24 2:33 ` Clem Cole
2020-09-27 5:54 ` Dave Horsfall
2020-09-24 17:19 ` Paul Winalski
2020-09-24 18:17 ` John Cowan
2020-10-07 5:47 ` scj
2020-10-07 9:20 ` arnold
2020-10-08 0:27 ` Dave Horsfall
2020-10-08 3:08 ` John Cowan
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