[PATCH] malloc: Deprecate more hook-related functionality

[Carlos O'Donell]

On 7/10/20 8:56 AM, Florian Weimer via Libc-alpha wrote:

OK for 2.32 with commit message fixed.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>

> __morecore, __after_morecore_hook and __after_morecore_hook had not

Suggest:

__morecore, __after_morecore_hook, and __default_morecore had not ...

> been deprecated in commit 7d17596c198f11fa85cbcf9587443f262e63b616
> ("Mark malloc hook variables as deprecated"), probably by accident.

In my original patch to remove the malloc hooks:
https://sourceware.org/pipermail/libc-alpha/2018-June/095230.html

I note the following:
~~~
The functionality which is no longer supported is that provided by
__morecore, and __after_morecore_hook. The morecore related hooking is
entirely removed, and __default_morecore is always called with no
interposition possible (now named __glibc_morecore).
...
	__morecore@GLIBC_2.2.5 (unused)
	__default_morecore@GLIBC_2.2.5 (default)
	__after_morecore_hook@GLIBC_2.2.5 (unused)
~~~

Your deprecation matches my expectations for additional functions
which would need deprecation, and matches my comments in the 2018 patch.

I appreciate your help here moving this interface towards removal.

> Tested on i686-linux-gnu.
> 
> ---
>  NEWS            | 7 +++++++
>  malloc/malloc.h | 7 ++++---
>  2 files changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/NEWS b/NEWS
> index 0b25b4fde9..8fb1dac36d 100644
> --- a/NEWS
> +++ b/NEWS
> @@ -131,6 +131,13 @@ Deprecated and removed features, and other changes affecting compatibility:
>    storing RPC keys only supported the obsolete and insecure AUTH_DES
>    flavor of secure RPC.)
>  
> +* The __morecore and __after_morecore_hook malloc hooks and the default
> +  implementation __default_morecore have been deprecated.  Applications
> +  should use malloc interposition to change malloc behavior, and mmap to
> +  allocate anonymous memory.  A future version of glibc may require that
> +  applications which use the malloc hooks must preload a special shared
> +  object, to enable the hooks.

OK.

> +
>  Changes to build and runtime requirements:
>  
>  * powerpc64le requires GCC 7.4 or newer.  This is required for supporting
> diff --git a/malloc/malloc.h b/malloc/malloc.h
> index a6903fdd54..e0e91a9331 100644
> --- a/malloc/malloc.h
> +++ b/malloc/malloc.h
> @@ -75,11 +75,11 @@ extern void *pvalloc (size_t __size) __THROW __attribute_malloc__ __wur;
>  
>  /* Underlying allocation function; successive calls should return
>     contiguous pieces of memory.  */
> -extern void *(*__morecore) (ptrdiff_t __size);
> +extern void *(*__morecore) (ptrdiff_t __size) __MALLOC_DEPRECATED;

OK.

>  
>  /* Default value of `__morecore'.  */
>  extern void *__default_morecore (ptrdiff_t __size)
> -__THROW __attribute_malloc__;
> +__THROW __attribute_malloc__  __MALLOC_DEPRECATED;

OK.

>  
>  /* SVID2/XPG mallinfo structure */
>  
> @@ -156,7 +156,8 @@ extern void *(*__MALLOC_HOOK_VOLATILE __memalign_hook)(size_t __alignment,
>                                                         size_t __size,
>                                                         const void *)
>  __MALLOC_DEPRECATED;
> -extern void (*__MALLOC_HOOK_VOLATILE __after_morecore_hook) (void);
> +extern void (*__MALLOC_HOOK_VOLATILE __after_morecore_hook) (void)
> +  __MALLOC_DEPRECATED;

OK.

>  
>  
>  __END_DECLS
> 


-- 
Cheers,
Carlos.