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Re: Initial draft proposal: "Safe arrays and pointers for C"

From Jens Gustedt <jens.gustedt@loria.fr>
Newsgroups comp.std.c
Subject Re: Initial draft proposal: "Safe arrays and pointers for C"
Date 2012-08-16 20:28 +0200
Organization A noiseless patient Spider
Message-ID <502D3BBA.1060807@loria.fr> (permalink)
References (6 earlier) <502ACC52.1060808@verizon.net> <MPG.2a94dc129cb7ed389896ba@news.eternal-september.org> <a922mmFctpU1@mid.dfncis.de> <MPG.2a961b2dcde5d55e9896bc@news.eternal-september.org> <a94o4dFjbgU1@mid.dfncis.de>

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Am 16.08.2012 19:14, schrieb Hans-Bernhard Bröker:
> On 16.08.2012 06:47, Philip Lantz wrote:
>> Hans-Bernhard Bröker wrote:
> 
>>> Given the fact you're talking about trashing every single ABI in
>>> existence, that's a pretty big "just".
> 
>> That's not what I'm talking about.
> 
>> I'm talking about an operator that will give the array size of a
>> parameter where the size is known, such as:
>>
>> void f1(int a[5])
>> void f2(int n, char b[n])
> 
> The implementor of f1 and f2 doesn't need any new operator to get at at
> _that_ information.  He can just write `5' or `n', respectively.
> 
> But that's OK, actually, because that is not the information needed to
> avoid buffer overflows, in the first place.  What you need is the size
> of the _actual_ argument, and that cannot possibly be known to any other
> party but the calling function.  Not in the general case, anyway.
> 
> So for that information to be available in the called function, it has
> to be passed to it some way.  This means the size of the actual array
> has to become a hidden argument to be passed to the function (a bit like
> the `this' pointer in C++ methods), and that's the change of ABI that
> you believe you're not talking about.

But there is just no need this information in the called function. As
far as I see, nowhere in C there is an obligation of the called
function to check for the validity of a parameter. It is always the
obligation for the calling side to provide the correct
arguments. (Think of printf, e.g)

And C has a construct for the first case (f1 above) that lets us name
an expectation about the size of the array that is to be passed to the
function, at least for the first case.

void f1(int a[static 5])

*makes* a difference to

void f1(int *a)

it tells the caller that at least 5 elements are expected. The ABI is
the same, but the semantic for the calling side has changed.

If the argument is indeed an array this is trivial to check:

int B[4] = { 0 };
f1(B);

This is UB. But it is easy to check even at compile time, so one could
constrain this without difficulties.

Nobody seems to have implemented this (at least I didn't receive an
answer for my question upthread.)

For

int C[n];  // n a variable
f1(C);

this can easily be checked at runtime and the bounds checking
interface of C11 could give a tool to handle this.

For

void f2(int n, char b[n])

the situation is a bit more complicated since, as you say, a
previously "meaningless" syntactic sugar all of a sudden receives a
meaning. (well only for the innermost dimenson, it well has one for
other dimensions.)

Here comes John's "strict mode". Don't change the meaning of the above
in normal compilation, but when in "strict mode" require that all
declarations and definitions agree on the expressions inside []. Then,
take these expressions for the check at the calling side. No need at
all to change the ABI, to transfer information to the called side or
anything like that.

Jens

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Thread

Initial draft proposal: "Safe arrays and pointers for C" John Nagle <nagle@animats.com> - 2012-08-13 11:39 -0700
  Re: Initial draft proposal: "Safe arrays and pointers for C" Jens Gustedt <jens.gustedt@loria.fr> - 2012-08-13 23:23 +0200
    Re: Initial draft proposal: "Safe arrays and pointers for C" Keith Thompson <kst-u@mib.org> - 2012-08-13 17:04 -0700
    Re: Initial draft proposal: "Safe arrays and pointers for C" John Nagle <nagle@animats.com> - 2012-08-13 20:08 -0700
      Re: Initial draft proposal: "Safe arrays and pointers for C" Keith Thompson <kst-u@mib.org> - 2012-08-13 22:23 -0700
        Re: Initial draft proposal: "Safe arrays and pointers for C" John Nagle <nagle@animats.com> - 2012-08-14 11:20 -0700
          Re: Initial draft proposal: "Safe arrays and pointers for C" James Kuyper <jameskuyper@verizon.net> - 2012-08-14 14:54 -0400
            Re: Initial draft proposal: "Safe arrays and pointers for C" Jens Gustedt <jens.gustedt@loria.fr> - 2012-08-14 21:09 +0200
              Re: Initial draft proposal: "Safe arrays and pointers for C" James Kuyper <jameskuyper@verizon.net> - 2012-08-14 16:00 -0400
            Re: Initial draft proposal: "Safe arrays and pointers for C" James Kuyper <jameskuyper@verizon.net> - 2012-08-14 18:08 -0400
              Re: Initial draft proposal: "Safe arrays and pointers for C" Philip Lantz <prl@canterey.us> - 2012-08-14 23:05 -0700
                Re: Initial draft proposal: "Safe arrays and pointers for C" James Kuyper <jameskuyper@verizon.net> - 2012-08-15 06:48 -0400
                Re: Initial draft proposal: "Safe arrays and pointers for C" John Nagle <nagle@animats.com> - 2012-08-15 11:22 -0700
                Re: Initial draft proposal: "Safe arrays and pointers for C" James Kuyper <jameskuyper@verizon.net> - 2012-08-15 15:13 -0400
                Re: Initial draft proposal: "Safe arrays and pointers for C" John Nagle <nagle@animats.com> - 2012-08-15 13:00 -0700
                Re: Initial draft proposal: "Safe arrays and pointers for C" Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2012-08-15 22:52 +0200
                Re: Initial draft proposal: "Safe arrays and pointers for C" James Kuyper <jameskuyper@verizon.net> - 2012-08-15 17:18 -0400
                Re: Initial draft proposal: "Safe arrays and pointers for C" Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2012-08-16 19:20 +0200
                Re: Initial draft proposal: "Safe arrays and pointers for C" James Kuyper <jameskuyper@verizon.net> - 2012-08-16 13:40 -0400
                Re: Initial draft proposal: "Safe arrays and pointers for C" Keith Thompson <kst-u@mib.org> - 2012-08-16 11:04 -0700
                Re: Initial draft proposal: "Safe arrays and pointers for C" James Kuyper <jameskuyper@verizon.net> - 2012-08-16 14:35 -0400
                Re: Initial draft proposal: "Safe arrays and pointers for C" Keith Thompson <kst-u@mib.org> - 2012-08-16 11:47 -0700
                Re: Initial draft proposal: "Safe arrays and pointers for C" James Kuyper <jameskuyper@verizon.net> - 2012-08-16 14:52 -0400
                Re: Initial draft proposal: "Safe arrays and pointers for C" Keith Thompson <kst-u@mib.org> - 2012-08-15 14:41 -0700
                Re: Initial draft proposal: "Safe arrays and pointers for C" "Derek M. Jones" <derek@_NOSPAM_knosof.co.uk> - 2012-08-16 12:39 +0100
                Re: Initial draft proposal: "Safe arrays and pointers for C" John Nagle <nagle@animats.com> - 2012-08-16 09:57 -0700
                Re: Initial draft proposal: "Safe arrays and pointers for C" James Kuyper <jameskuyper@verizon.net> - 2012-08-16 13:28 -0400
                Re: Initial draft proposal: "Safe arrays and pointers for C" "Derek M. Jones" <derek@_NOSPAM_knosof.co.uk> - 2012-08-16 23:52 +0100
                Re: Initial draft proposal: "Safe arrays and pointers for C" Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2012-08-15 18:56 +0200
                Re: Initial draft proposal: "Safe arrays and pointers for C" jacob navia <jacob@spamsink.net> - 2012-08-15 19:23 +0200
                Re: Initial draft proposal: "Safe arrays and pointers for C" Philip Lantz <prl@canterey.us> - 2012-08-15 21:47 -0700
                Re: Initial draft proposal: "Safe arrays and pointers for C" Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2012-08-16 19:14 +0200
                Re: Initial draft proposal: "Safe arrays and pointers for C" Jens Gustedt <jens.gustedt@loria.fr> - 2012-08-16 20:28 +0200
          Re: Initial draft proposal: "Safe arrays and pointers for C" James Kuyper <jameskuyper@verizon.net> - 2012-08-14 15:05 -0400
          Re: Initial draft proposal: "Safe arrays and pointers for C" Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2012-08-14 21:09 +0200
            Re: Initial draft proposal: "Safe arrays and pointers for C" John Nagle <nagle@animats.com> - 2012-08-14 13:24 -0700
              Re: Initial draft proposal: "Safe arrays and pointers for C" James Kuyper <jameskuyper@verizon.net> - 2012-08-14 16:39 -0400
              Re: Initial draft proposal: "Safe arrays and pointers for C" Keith Thompson <kst-u@mib.org> - 2012-08-14 15:23 -0700
                Re: Initial draft proposal: "Safe arrays and pointers for C" Philip Lantz <prl@canterey.us> - 2012-08-14 22:58 -0700
              Re: Initial draft proposal: "Safe arrays and pointers for C" Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2012-08-15 00:37 +0200
                Re: Initial draft proposal: "Safe arrays and pointers for C" Keith Thompson <kst-u@mib.org> - 2012-08-14 16:42 -0700
                Re: Initial draft proposal: "Safe arrays and pointers for C" Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2012-08-15 22:57 +0200
                Re: Initial draft proposal: "Safe arrays and pointers for C" Keith Thompson <kst-u@mib.org> - 2012-08-15 17:02 -0700
          Re: Initial draft proposal: "Safe arrays and pointers for C" Keith Thompson <kst-u@mib.org> - 2012-08-14 14:59 -0700
            Re: Initial draft proposal: "Safe arrays and pointers for C" John Nagle <nagle@animats.com> - 2012-08-14 15:35 -0700
              Re: Initial draft proposal: "Safe arrays and pointers for C" Jens Gustedt <jens.gustedt@loria.fr> - 2012-08-15 00:51 +0200
                Re: Initial draft proposal: "Safe arrays and pointers for C" jacob navia <jacob@spamsink.net> - 2012-08-15 06:43 +0200
                Re: Initial draft proposal: "Safe arrays and pointers for C" Jens Gustedt <jens.gustedt@loria.fr> - 2012-08-15 08:31 +0200
                Re: Initial draft proposal: "Safe arrays and pointers for C" jacob navia <jacob@spamsink.net> - 2012-08-15 09:14 +0200
              Re: Initial draft proposal: "Safe arrays and pointers for C" James Kuyper <jameskuyper@verizon.net> - 2012-08-14 18:58 -0400
                Re: Initial draft proposal: "Safe arrays and pointers for C" jacob navia <jacob@spamsink.net> - 2012-08-15 06:45 +0200
                Re: Initial draft proposal: "Safe arrays and pointers for C" Philip Lantz <prl@canterey.us> - 2012-08-14 22:51 -0700
                Re: Initial draft proposal: "Safe arrays and pointers for C" James Kuyper <jameskuyper@verizon.net> - 2012-08-15 07:18 -0400
                Re: Initial draft proposal: "Safe arrays and pointers for C" Jens Gustedt <jens.gustedt@loria.fr> - 2012-08-15 14:15 +0200
                Re: Initial draft proposal: "Safe arrays and pointers for C" jacob navia <jacob@spamsink.net> - 2012-08-15 14:28 +0200
                Re: Initial draft proposal: "Safe arrays and pointers for C" Jens Gustedt <jens.gustedt@loria.fr> - 2012-08-15 14:36 +0200
                Re: Initial draft proposal: "Safe arrays and pointers for C" jacob navia <jacob@spamsink.net> - 2012-08-15 14:54 +0200
                Re: Initial draft proposal: "Safe arrays and pointers for C" Jens Gustedt <jens.gustedt@loria.fr> - 2012-08-15 15:08 +0200
                Re: Initial draft proposal: "Safe arrays and pointers for C" Keith Thompson <kst-u@mib.org> - 2012-08-15 12:50 -0700
                Re: Initial draft proposal: "Safe arrays and pointers for C" Jens Gustedt <jens.gustedt@loria.fr> - 2012-08-15 23:22 +0200
                Re: Initial draft proposal: "Safe arrays and pointers for C" John Nagle <nagle@animats.com> - 2012-08-15 14:38 -0700
                Re: Initial draft proposal: "Safe arrays and pointers for C" Jens Gustedt <jens.gustedt@loria.fr> - 2012-08-16 00:51 +0200
                Re: Initial draft proposal: "Safe arrays and pointers for C" John Nagle <nagle@animats.com> - 2012-08-15 16:32 -0700
                Re: Initial draft proposal: "Safe arrays and pointers for C" Jens Gustedt <jens.gustedt@loria.fr> - 2012-08-16 09:05 +0200
                Re: Initial draft proposal: "Safe arrays and pointers for C" Keith Thompson <kst-u@mib.org> - 2012-08-15 17:22 -0700
                Re: Initial draft proposal: "Safe arrays and pointers for C" John Nagle <nagle@animats.com> - 2012-08-15 20:29 -0700
                Re: Initial draft proposal: "Safe arrays and pointers for C" Keith Thompson <kst-u@mib.org> - 2012-08-15 12:36 -0700
                Re: Initial draft proposal: "Safe arrays and pointers for C" James Kuyper <jameskuyper@verizon.net> - 2012-08-15 16:09 -0400
                Re: Initial draft proposal: "Safe arrays and pointers for C" Jens Gustedt <jens.gustedt@loria.fr> - 2012-08-15 08:47 +0200
              Re: Initial draft proposal: "Safe arrays and pointers for C" Keith Thompson <kst-u@mib.org> - 2012-08-14 16:33 -0700
                Re: Initial draft proposal: "Safe arrays and pointers for C" Keith Thompson <kst-u@mib.org> - 2012-08-14 16:38 -0700
                Re: Initial draft proposal: "Safe arrays and pointers for C" jacob navia <jacob@spamsink.net> - 2012-08-15 06:46 +0200
                Re: Initial draft proposal: "Safe arrays and pointers for C" Keith Thompson <kst-u@mib.org> - 2012-08-14 22:28 -0700
                Re: Initial draft proposal: "Safe arrays and pointers for C" Jens Gustedt <jens.gustedt@loria.fr> - 2012-08-15 08:34 +0200
                Re: Initial draft proposal: "Safe arrays and pointers for C" jacob navia <jacob@spamsink.net> - 2012-08-15 09:12 +0200
          Re: Initial draft proposal: "Safe arrays and pointers for C" John Nagle <nagle@animats.com> - 2012-08-16 13:09 -0700
            Re: Initial draft proposal: "Safe arrays and pointers for C" Wojtek Lerch <wojtek_l@yahoo.ca> - 2012-08-16 16:21 -0400
              Re: Initial draft proposal: "Safe arrays and pointers for C" John Nagle <nagle@animats.com> - 2012-08-16 14:22 -0700
                Re: Initial draft proposal: "Safe arrays and pointers for C" Keith Thompson <kst-u@mib.org> - 2012-08-16 15:28 -0700
                Re: Initial draft proposal: "Safe arrays and pointers for C" Wojtek Lerch <wojtek_l@yahoo.ca> - 2012-08-16 19:49 -0400
      Re: Initial draft proposal: "Safe arrays and pointers for C" Jens Gustedt <jens.gustedt@loria.fr> - 2012-08-14 08:56 +0200
      Re: Initial draft proposal: "Safe arrays and pointers for C" James Kuyper <jameskuyper@verizon.net> - 2012-08-14 06:18 -0400
        Re: Initial draft proposal: "Safe arrays and pointers for C" Jens Gustedt <jens.gustedt@loria.fr> - 2012-08-14 12:42 +0200
          Re: Initial draft proposal: "Safe arrays and pointers for C" John Nagle <nagle@animats.com> - 2012-08-14 09:43 -0700
            Re: Initial draft proposal: "Safe arrays and pointers for C" Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2012-08-14 19:52 +0200
              Re: Initial draft proposal: "Safe arrays and pointers for C" jacob navia <jacob@spamsink.net> - 2012-08-14 21:03 +0200
            Re: Initial draft proposal: "Safe arrays and pointers for C" Jens Gustedt <jens.gustedt@loria.fr> - 2012-08-14 21:39 +0200
      Re: Initial draft proposal: "Safe arrays and pointers for C" Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-08-14 08:26 -0400
  Re: Initial draft proposal: "Safe arrays and pointers for C" Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-08-13 22:44 +0100
    Re: Initial draft proposal: "Safe arrays and pointers for C" John Nagle <nagle@animats.com> - 2012-08-13 18:05 -0700
  Re: Initial draft proposal: "Safe arrays and pointers for C" jacob navia <jacob@spamsink.net> - 2012-08-14 21:00 +0200
    Re: Initial draft proposal: "Safe arrays and pointers for C" Marc <marc.glisse@gmail.com> - 2012-08-14 21:18 +0000
      Re: Initial draft proposal: "Safe arrays and pointers for C" jacob navia <jacob@spamsink.net> - 2012-08-14 23:51 +0200
  Re: Initial draft proposal: "Safe arrays and pointers for C" John Nagle <nagle@animats.com> - 2012-08-17 09:40 -0700
    Re: Initial draft proposal: "Safe arrays and pointers for C" Jens Gustedt <jens.gustedt@loria.fr> - 2012-08-17 21:00 +0200
      Re: Initial draft proposal: "Safe arrays and pointers for C" John Nagle <nagle@animats.com> - 2012-08-17 13:30 -0700
        Re: Initial draft proposal: "Safe arrays and pointers for C" jacob navia <jacob@spamsink.net> - 2012-08-17 23:14 +0200
        Re: Initial draft proposal: "Safe arrays and pointers for C" Jens Gustedt <jens.gustedt@loria.fr> - 2012-08-18 01:07 +0200
          Re: Initial draft proposal: "Safe arrays and pointers for C" John Nagle <nagle@animats.com> - 2012-08-19 23:14 -0700
            Re: Initial draft proposal: "Safe arrays and pointers for C" Ike Naar <ike@sverige.freeshell.org> - 2012-08-20 07:16 +0000
              Re: Initial draft proposal: "Safe arrays and pointers for C" John Nagle <nagle@animats.com> - 2012-08-20 00:25 -0700
            Re: Initial draft proposal: "Safe arrays and pointers for C" Jens Gustedt <jens.gustedt@loria.fr> - 2012-08-20 11:49 +0200
            Re: Initial draft proposal: "Safe arrays and pointers for C" Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2012-08-20 22:40 +0200
              Re: Initial draft proposal: "Safe arrays and pointers for C" jacob navia <jacob@spamsink.net> - 2012-08-20 23:08 +0200
    Re: Initial draft proposal: "Safe arrays and pointers for C" Keith Thompson <kst-u@mib.org> - 2012-08-17 15:33 -0700

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