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

[Stephen Kitt <steve@sk2.org>]

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On Sat, 8 Jan 2022 11:30:41 +0100, Jakub Wilk <jwilk@jwilk.net> wrote:
> 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.

Agreed, the example is just trying to pass an int into the function given to
pthread_create. AFAICT the only requirement for correctness is that the type
used is at most the size of void *.

It’s probably not worth bothering about the compiler warning...

Regards,

Stephen

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