Re: [PATCH 01/28] elf: Do not search HWCAP subdirectories in statically linked binaries

[Adhemerval Zanella <adhemerval.zanella@linaro.org>]

On 01/10/2020 13:31, Florian Weimer via Libc-alpha wrote:
> This functionality does not seem to be useful since static dlopen
> is mostly used for iconv/character set conversion and NSS support.
> gconv modules are loaded with full paths anyway, so that the
> HWCAP subdirectory logic does not apply.

This change looks reasonable, although it makes the semantic of 
statically linked programs slight different than dynamic one regarding
dlopen.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

> ---
>  NEWS          |  4 ++++
>  elf/Makefile  |  4 ++--
>  elf/dl-load.c | 14 ++++++++++++++
>  3 files changed, 20 insertions(+), 2 deletions(-)
> 
> diff --git a/NEWS b/NEWS
> index ce05d05b16..902fa3a7f8 100644
> --- a/NEWS
> +++ b/NEWS
> @@ -33,6 +33,10 @@ Deprecated and removed features, and other changes affecting compatibility:
>  * The mallinfo function is marked deprecated.  Callers should call
>    mallinfo2 instead.
>  
> +* When dlopen is used in statically linked programs, alternative library
> +  implementations from HWCAP subdirectories are no longer loaded.
> +  Instead, the default implementation is used.
> +
>  Changes to build and runtime requirements:
>  
>    [Add changes to build and runtime requirements here]

Ok.

> diff --git a/elf/Makefile b/elf/Makefile
> index c587e9f06e..e0a8bf2998 100644
> --- a/elf/Makefile
> +++ b/elf/Makefile
> @@ -29,7 +29,7 @@ routines	= $(all-dl-routines) dl-support dl-iteratephdr \
>  
>  # The core dynamic linking functions are in libc for the static and
>  # profiled libraries.
> -dl-routines	= $(addprefix dl-,load lookup object reloc deps hwcaps \
> +dl-routines	= $(addprefix dl-,load lookup object reloc deps \
>  				  runtime init fini debug misc \
>  				  version profile tls origin scope \
>  				  execstack open close trampoline \

Ok.

> @@ -59,7 +59,7 @@ elide-routines.os = $(all-dl-routines) dl-support enbl-secure dl-origin \
>  # ld.so uses those routines, plus some special stuff for being the program
>  # interpreter and operating independent of libc.
>  rtld-routines	= rtld $(all-dl-routines) dl-sysdep dl-environ dl-minimal \
> -  dl-error-minimal dl-conflict
> +  dl-error-minimal dl-conflict dl-hwcaps
>  all-rtld-routines = $(rtld-routines) $(sysdep-rtld-routines)
>  
>  CFLAGS-dl-runtime.c += -fexceptions -fasynchronous-unwind-tables

Ok.

> diff --git a/elf/dl-load.c b/elf/dl-load.c
> index 646c5dca40..5ba117d597 100644
> --- a/elf/dl-load.c
> +++ b/elf/dl-load.c
> @@ -101,9 +101,13 @@ int __stack_prot attribute_hidden attribute_relro
>  static struct r_search_path_struct env_path_list attribute_relro;
>  
>  /* List of the hardware capabilities we might end up using.  */
> +#ifdef SHARED
>  static const struct r_strlenpair *capstr attribute_relro;
>  static size_t ncapstr attribute_relro;
>  static size_t max_capstrlen attribute_relro;
> +#else
> +enum { ncapstr = 1, max_capstrlen = 0 };
> +#endif
>  
>  
>  /* Get the generated information about the trusted directories.  Use

Ok.

> @@ -691,9 +695,11 @@ _dl_init_paths (const char *llp)
>    /* Fill in the information about the application's RPATH and the
>       directories addressed by the LD_LIBRARY_PATH environment variable.  */
>  
> +#ifdef SHARED
>    /* Get the capabilities.  */
>    capstr = _dl_important_hwcaps (GLRO(dl_platform), GLRO(dl_platformlen),
>  				 &ncapstr, &max_capstrlen);
> +#endif
>  
>    /* First set up the rest of the default search directory entries.  */
>    aelem = rtld_search_dirs.dirs = (struct r_search_path_elem **)
> @@ -1521,11 +1527,15 @@ print_search_path (struct r_search_path_elem **list,
>        for (cnt = 0; cnt < ncapstr; ++cnt)
>  	if ((*list)->status[cnt] != nonexisting)
>  	  {
> +#ifdef SHARED
>  	    char *cp = __mempcpy (endp, capstr[cnt].str, capstr[cnt].len);
>  	    if (cp == buf || (cp == buf + 1 && buf[0] == '/'))
>  	      cp[0] = '\0';
>  	    else
>  	      cp[-1] = '\0';
> +#else
> +	    *endp = '\0';
> +#endif
>  
>  	    _dl_debug_printf_c (first ? "%s" : ":%s", buf);
>  	    first = 0;
> @@ -1886,11 +1896,15 @@ open_path (const char *name, size_t namelen, int mode,
>  	  if (this_dir->status[cnt] == nonexisting)
>  	    continue;
>  
> +#ifdef SHARED
>  	  buflen =
>  	    ((char *) __mempcpy (__mempcpy (edp, capstr[cnt].str,
>  					    capstr[cnt].len),
>  				 name, namelen)
>  	     - buf);
> +#else
> +	  buflen = (char *) __mempcpy (edp, name, namelen) - buf;
> +#endif
>  
>  	  /* Print name we try if this is wanted.  */
>  	  if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_LIBS))
> 

Ok.