When should ralloc.c be used? (WAS: bug#24358)

[npostavs]

Eli Zaretskii <address@hidden> writes:
>>     Thread 1 "emacs" hit Hardware watchpoint 4: current_buffer->text->beg
>> 
>>     Old value = (unsigned char *) 0x18351b8 ""
>>     New value = (unsigned char *) 0x188a1b8 ""
>>     r_alloc_sbrk (size=290816) at ralloc.c:818
>
> r_alloc_sbrk?  What OS is this?  We only use ralloc.c on a handful of
> them, as of Emacs 25.

Should ralloc.c be used on GNU/Linux systems that have GNU libc?

I found this in my config.log (I think it's related to ralloc use,
though I'm finding the configure code a bit confusing):

    configure:11440: checking whether malloc is Doug Lea style
    configure:11461: gcc -o conftest -O0 -g3 -march=native     conftest.c  >&5 
    conftest.c: In function 'main':
    conftest.c:107:6: error: '__malloc_initialize_hook' undeclared (first use 
in this function)
          __malloc_initialize_hook = hook;
          ^~~~~~~~~~~~~~~~~~~~~~~~

It seems that my malloc.h does not declare __malloc_initialize_hook,
even though 'man 3 malloc_hook' says

       #include <malloc.h>

       void *(*__malloc_hook)(size_t size, const void *caller);

       void *(*__realloc_hook)(void *ptr, size_t size, const void *caller);

       void *(*__memalign_hook)(size_t alignment, size_t size,
                                const void *caller);

       void (*__free_hook)(void *ptr, const void *caller);

       void (*__malloc_initialize_hook)(void);

       void (*__after_morecore_hook)(void);

Perhaps this is because the recommended way to set this hook (which is
different from what the configure test is using) doesn't require a
declaration?

       The variable __malloc_initialize_hook points at a function that is 
called once when the  mal‐
       loc  implementation  is initialized.  This is a weak variable, so it can 
be overridden in the
       application with a definition like the following:

           void (*__malloc_initialize_hook)(void) = my_init_hook;