Re: [PATCH 9/9] malloc_info.3: Use intptr_t to store pointers

[Jakub Wilk <jwilk@jwilk.net>]

For the record, this is what you get when you compile the original code 
on a 64-bit architecture:

    $ gcc -Wall -pthread malloc_info-example.c
    malloc_info-example.c: In function 'thread_func':
    malloc_info-example.c:16:14: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
       16 |     int tn = (int) arg;
          |              ^
    malloc_info-example.c: In function 'main':
    malloc_info-example.c:57:32: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
       57 |                                (void *) tn);
          |                                ^

* Alejandro Colomar <alx.manpages@gmail.com>, 2022-01-08, 03:25:
>On 1/7/22 17:46, Stephen Kitt wrote:
>>int isn't large enough to store pointers on all platforms, use 
>>intptr_t instead.
>
>Well, since the pointer came from a previous 'int', there should be no 
>problem.  But since the C language (or even POSIX) is very permissive 
>about what a conforming implementation can do with pointers, and it 
>only guarantees conversions to/from [u]intptr_t, I'd take this patch 
>for correctness.  However...

The standards guarantee that void* → intptr_t → void* round-trips, 
but that's not what this code does.

The example converts int → void* → int. Changing int to intptr_t makes 
the compiler warnings go away, but I don't think it improves correctness 
in any way.

-- 
Jakub Wilk