From: Clem Cole <clemc@ccc.com>
To: Rob Pike <robpike@gmail.com>
Cc: The Eunuchs Hysterical Society <tuhs@tuhs.org>
Subject: Re: [TUHS] reviving a bit of WWB
Date: Mon, 21 Sep 2020 17:57:00 -0400 [thread overview]
Message-ID: <CAC20D2Nmrrt-Hnd6M+BF+pX-su5rfZ1m31xtWUjymUDBDnsV+g@mail.gmail.com> (raw)
In-Reply-To: <CAKzdPgwD2s9SbKQgRa46S_kVCVXC7-_bqEn9UMHGb9Zve1=x2g@mail.gmail.com>
[-- Attachment #1: Type: text/plain, Size: 2342 bytes --]
Right .. I remember running into/using that idiom in a couple of places in
a few other drivers in the early years. I also remember working one of the
CAD tools (it may have been one of the UCB CAD editors) which were very
graphics centric and running into it there.
I always looked at this as part of the original C heritage from simpler
times *i.e.* from ESPOL/BCPL/B and the like, when it was still considered a
'low level' language that mapped well to the HW at hand. As the more and
more features got added, the focus of the language changed ... ney
Chisnall's 2018 screed: C is not a low level language
<https://queue.acm.org/detail.cfm?id=3212479> Not nearly as bad as the
pile we got with 'modern' C++ [which I'm loath to use].
Clem
On Mon, Sep 21, 2020 at 5:23 PM Rob Pike <robpike@gmail.com> wrote:
> 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 21:58 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
2020-09-21 21:57 ` Clem Cole [this message]
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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