Re: [tor-dev] building from source in a 64-bit windows environment..

[not me <anemenja@xxxxxxxxx>]

> There's nothing wrong with sizeof(long) == sizeof(int),

Agreed.

> but I assure you that C89 does require sizeof(long) >= sizeof(void *)

Really? where? It doesn't seem to be in the C89 standard I just flipped through.
I flipped through it because this sounded horribly wrong. Here's what I found:

"7.18.1.4 Integer types capable of holding object pointers

1 The following type designates a signed integer type with the
property that any valid
pointer to void can be converted to this type, then converted back to
pointer to void,
and the result will compare equal to the original pointer:

intptr_t

The following type designates an unsigned integer type with the
property that any valid
pointer to void can be converted to this type, then converted back to
pointer to void,
and the result will compare equal to the original pointer:

uintptr_t

These types are optional."

Moreover, there is a warning in annex I relating to truncation when
converting long/int/etc to a pointer of anything other than char* and
vice versa.

In other words, I think you've imagined this requirement.

> [more precisely, that a valid value of type 'void*' can be cast to 'unsigned long' and back without loss of information]

The phrase 'void*' doesnt appear in C89, all references to 'pointer to
void', or 'void *'. Furthermore of the 44 references to unsigned long
in C89, not a single one even references pointers to void, much less
this absolutely absurd notion you have that converting pointers to
integer types is safe and good programming practice.

> It is not itself a spelled-out requirement in
> the standard, [....]

so our absolute guarantee that its in the standard is actually you
reading between the lines?

> but it follows from two requirements which are explicitly stated. First, 'size_t' is required to be able to represent the size of any object;

Indeed, why do we even need a size_t, we have an unsigned long!


> Second, 'size_t' is required to be no larger than 'unsigned long'.

Not sure if you're saying that this is in the standard or if MSFT used
its evil tentacles to have its removed, but no, the standard says its
size is implementation defined. I *think* what you're referencing is
possible this:

"The types used for size_t and ptrdiff_t should not have an integer
conversion rank
greater than that of signed long int unless the implementation supports objects
large enough to make this necessary."

"supports objects large enough to make this necessary" AKA 64-bit.

>  and you still can't use %zu in printf.

You can't use %n either

> Yes, I am still bitter.

Wrong people usually are.


On Sat, May 18, 2013 at 11:55 AM, Zack Weinberg <zackw@xxxxxxxxx> wrote:
> On Sat, May 18, 2013 at 11:19 AM, Anthony Martin <ality@xxxxxxxxxx> wrote:
>> Zack Weinberg <zackw@xxxxxxxxx> once said:
>>> * Win64 is the *only* flat-memory-space ABI ever promulgated in
>>>   which pointers cannot safely be converted to 'unsigned long'
>>>   and back without loss of information.  This is a willful
>>>   violation of requirements in C89 and is IMNSHO sufficient
>>>   justification to refuse to port to this platform, all by itself.
>>
>> This is just wrong. There's nothing wrong with having long
>> be the same size as int. And Windows isn't the only 64-bit
>> platform that does it. Plan 9 works the same way.
>
> There's nothing wrong with sizeof(long) == sizeof(int), but I assure
> you that C89 does require sizeof(long) >= sizeof(void *) [more
> precisely, that a valid value of type 'void*' can be cast to 'unsigned
> long' and back without loss of information] provided also that the
> memory space is flat.  It is not itself a spelled-out requirement in
> the standard, but it follows from two requirements which are
> explicitly stated. First, 'size_t' is required to be able to represent
> the size of any object; when the memory space is flat, this entails
> that 'void*' can be cast to 'size_t' and back without loss of
> information.  Second, 'size_t' is required to be no larger than
> 'unsigned long'.
>
> For further exposition, please see comp.std.c archives in the time
> period leading up to C99.  This was argued over in great detail
> because Microsoft forced the C committee to remove the second of the
> above two requirements from C99, over basically everyone else's
> objections, precisely so they could say the Win64 ABI wasn't a C
> conformance violation, *and then didn't implement any of the C99
> features that would have made this less of a catastrophe for people
> trying to write portable code*.  <stdint.h> was only added to MSVC in
> the 2010 edition (and only because C++ picked it up); there's still no
> <inttypes.h> and you still can't use %zu in printf.
>
> Yes, I am still bitter.
> zw
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