Re: Bogus (intptr_t) casts

[Chet Ramey]

On 8/1/24 4:12 AM, Martin D Kealey wrote:


> It follows that the following assertions are allowed to fail:
>
>    intptr_t i = 0;
>    assert(*(void*)i == (void*)0*);
>    void *p = 0;
>    assert(*(intptr_t)p == 0*);
>
> Accordingly I provide the following patch:

I'm wondering why you chose these two cases, since there are other very
similar uses of intptr_t casts.

> diff --git a/*subst.c* b/subst.c
> index 37e0bfa7..140a3a92 100644
> --- a/subst.c
> +++ b/subst.c
> @@ -6875,7 +6875,7 @@ uw_restore_pipeline (void *discard)
>   static void
>   uw_restore_errexit (void *eflag)
>   {
>
> *-  change_flag ('e', (intptr_t) eflag ? FLAG_ON : FLAG_OFF);+  change_flag
> ('e', eflag ? FLAG_ON : FLAG_OFF);*
>     set_shellopts ();
>   }
>
> diff --git a/*variables.c* b/variables.c
> index cd336c85..d44453fe 100644
> --- a/variables.c
> +++ b/variables.c
> @@ -5444,7 +5444,7 @@ pop_scope (void *is_special)
>     FREE (vcxt->name);
>     if (vcxt->table)
>       {
>
> *-      if ((intptr_t) is_special)+      if (is_special)*
>          hash_flush (vcxt->table, push_builtin_var);
>         else
>          hash_flush (vcxt->table, push_exported_var);

You might want to look at the unwind-protect implementation, which doesn't
use assignments. It uses byte copies, so instead of using an assignment of,
say, 0, where the compiler can assign whatever it wants to denote a NULL
pointer, it copies 4-8 bytes, depending on the size of an integer. The cast
of that memory back to an intptr_t should be transparent on all reasonably
common systems.

Of course, if you can provide an example where it fails, I'll look at it
and fix it.

--
``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU    chet@case.edu    http://tiswww.cwru.edu/~chet/

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