elf: Remove LD_USE_LOAD_BIAS

It is solely for prelink with PIE executables [1].

[1] https://sourceware.org/legacy-ml/libc-hacker/2003-11/msg00127.html

Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

NEWS

@@ -197,6 +197,9 @@ Deprecated and removed features, and other changes affecting compatibility:
   functionality to obtain the program mapping address can be achieved by
   using LD_TRACE_LOADED_OBJECTS to value of 2.
 
+* The LD_USE_LOAD_BIAS has been removed.  The variable was mainly used to
+  support prelink PIE binaries.
+
 Changes to build and runtime requirements:
 
 * The audit module interface version LAV_CURRENT is increased to enable

elf/dl-map-segments.h

@@ -94,8 +94,7 @@ _dl_map_segments (struct link_map *l, int fd,
          prefer to map such objects at; but this is only a preference,
          the OS can do whatever it likes. */
       ElfW(Addr) mappref
-        = (ELF_PREFERRED_ADDRESS (loader, maplength,
+        = (ELF_PREFERRED_ADDRESS (loader, maplength, c->mapstart)
-                                  c->mapstart & GLRO(dl_use_load_bias))
            - MAP_BASE_ADDR (l));
 
       /* Remember which part of the address space this object uses.  */

elf/dl-support.c

@@ -54,7 +54,6 @@ size_t _dl_platformlen;
 
 int _dl_debug_mask;
 int _dl_lazy;
-ElfW(Addr) _dl_use_load_bias = -2;
 int _dl_dynamic_weak;
 
 /* If nonzero print warnings about problematic situations.  */

elf/rtld.c

@@ -365,7 +365,6 @@ struct rtld_global_ro _rtld_global_ro attribute_relro =
     ._dl_sysinfo = DL_SYSINFO_DEFAULT,
 #endif
     ._dl_debug_fd = STDERR_FILENO,
-    ._dl_use_load_bias = -2,
     ._dl_correct_cache_id = _DL_CACHE_DEFAULT_ID,
 #if !HAVE_TUNABLES
     ._dl_hwcap_mask = HWCAP_IMPORTANT,
@@ -1742,12 +1741,6 @@ dl_main (const ElfW(Phdr) *phdr,
   ++GL(dl_ns)[LM_ID_BASE]._ns_nloaded;
   ++GL(dl_load_adds);
 
-  /* If LD_USE_LOAD_BIAS env variable has not been seen, default
-     to not using bias for non-prelinked PIEs and libraries
-     and using it for executables or prelinked PIEs or libraries.  */
-  if (GLRO(dl_use_load_bias) == (ElfW(Addr)) -2)
-    GLRO(dl_use_load_bias) = main_map->l_addr == 0 ? -1 : 0;
-
   /* Starting from binutils-2.23, the linker will define the magic symbol
      __ehdr_start to point to our own ELF header if it is visible in a
      segment that also includes the phdrs.  If that's not available, we use
@@ -2657,12 +2650,6 @@ process_envvars (struct dl_main_state *state)
 #ifdef EXTRA_LD_ENVVARS_13
 	  EXTRA_LD_ENVVARS_13
 #endif
-	  if (!__libc_enable_secure
-	      && memcmp (envline, "USE_LOAD_BIAS", 13) == 0)
-	    {
-	      GLRO(dl_use_load_bias) = envline[14] == '1' ? -1 : 0;
-	      break;
-	    }
 	  break;
 
 	case 14:

sysdeps/generic/ldsodefs.h

@@ -628,11 +628,6 @@ struct rtld_global_ro
   /* Location of the binary.  */
   EXTERN const char *_dl_origin_path;
 
-  /* -1 if the dynamic linker should honor library load bias,
-     0 if not, -2 use the default (honor biases for normal
-     binaries, don't honor for PIEs).  */
-  EXTERN ElfW(Addr) _dl_use_load_bias;
-
   /* Size of the static TLS block.  */
   EXTERN size_t _dl_tls_static_size;
 

sysdeps/generic/unsecvars.h

@@ -22,7 +22,6 @@
   "LD_PRELOAD\0"							      \
   "LD_PROFILE\0"							      \
   "LD_SHOW_AUXV\0"							      \
-  "LD_USE_LOAD_BIAS\0"							      \
   "LOCALDOMAIN\0"							      \
   "LOCPATH\0"								      \
   "MALLOC_TRACE\0"							      \