ping //Re: [PATCH v2] elf: Sort only uninitialized objects in _dl_map_object_deps()

[Xiaoming Ni]

ping

On 2020/8/17 20:09, Xiaoming Ni wrote:
> TIS ELF Version 1.2
> Initialization and Termination Functions:
> 	1. Before the initialization code for any object A is called, the
> 	   initialization code for any other objects that object A depends
> 	   on are called.
> 	2. The order in which the dynamic linker calls termination functions
> 	   is the exact reverse order of their corresponding initialization
> 	   functions.
> 	3. The dynamic linker ensures that it will not execute any
> 	   initialization or termination functions more than once.
> 
> According to 1 and 2: _dl_sort_maps() is used for sorting when dlopen/dlclose.
> According to 3: At dlopen, only the uninitialized objects need to be sorted.
> 
> v1: https://public-inbox.org/libc-alpha/20200725105205.103328-1-nixiaoming@huawei.com/
> The new function _dl_sort_uninit_maps():
>   sorts the linked list based on whether the object has been initialized,
> 
> v2:
> the Chung-Lin Tang patch has optimized the sorting algorithm complexity to
> linear:
> 	https://patchwork.sourceware.org/project/glibc/patch/1427b370-7400-afd0-16e8-55c1072db20e@mentor.com/
> 	https://patchwork.sourceware.org/project/glibc/patch/5de3ab61-3dca-b400-15c6-92ff5ae80877@mentor.com/
> When the algorithm complexity of _dl_sort_maps() has been optimized, the benefits brought by
> _dl_sort_uninit_maps() are not obvious.
> 	https://public-inbox.org/libc-alpha/accfd786-0d1e-bb27-d950-76ab30633767@mentor.com/
> so _dl_sort_uninit_maps() is deleted from v2.
> Avoid unnecessary sorting only when the entire linked list has been initialized.
> ---
>   elf/dl-deps.c | 15 ++++++++++++++-
>   1 file changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/elf/dl-deps.c b/elf/dl-deps.c
> index b5a43232a7..8f377302bf 100644
> --- a/elf/dl-deps.c
> +++ b/elf/dl-deps.c
> @@ -611,7 +611,20 @@ Filters not supported with LD_TRACE_PRELINKING"));
>       memcpy (l_initfini, map->l_searchlist.r_list,
>   	    nlist * sizeof (struct link_map *));
>   
> -  _dl_sort_maps (&l_initfini[1], nlist - 1, NULL, false);
> +  /* TIS  ELF Version 1.2
> +   * Initialization and Termination Functions:
> +   * 1. Before the initialization code for any object A is called, the
> +   *  initialization code for any other objects that object A depends on are called.
> +   * 2. The order in which the dynamic linker calls termination functions is the
> +   *  exact reverse order of their corresponding initialization functions.
> +   * 3. The dynamic linker ensures that it will not execute any initialization
> +   *  or termination functions more than once.
> +   *
> +   * According to 1 and 2, _dl_sort_maps() is used for sorting when dlopen/dlclose.
> +   * According to 3, we only need to sort the uninitialized objects.
> +   */
> +  if (map->l_init_called == 0)
> +    _dl_sort_maps (&l_initfini[1], nlist - 1, NULL, false);
>   
>     /* Terminate the list of dependencies.  */
>     l_initfini[nlist] = NULL;
>