[glibc/nsz/bug27072] csu: Move static pie self relocation later [BZ #27072]

[Szabolcs Nagy <nsz@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=6b468d65b6c580acd82218b88b4150729c8921b2

commit 6b468d65b6c580acd82218b88b4150729c8921b2
Author: Szabolcs Nagy <szabolcs.nagy@arm.com>
Date:   Wed Jan 6 14:28:02 2021 +0000

    csu: Move static pie self relocation later [BZ #27072]
    
    IFUNC resolvers may depend on tunables and cpu feature setup so
    move static pie self relocation after those.
    
    It is hard to guarantee that the ealy startup code does not rely
    on relocations so this is a bit fragile. It would be more robust
    to handle RELATIVE relocs early and only IRELATIVE relocs later,
    but the current relocation processing code cannot do that.
    
    The early startup code up to relocation processing includes
    
      _dl_aux_init (auxvec);
      __libc_init_secure ();
      __tunables_init (__environ);
      ARCH_INIT_CPU_FEATURES ();
      _dl_relocate_static_pie ();
    
    These are simple enough that RELATIVE relocs can be avoided.
    
    The following steps include
    
      ARCH_SETUP_IREL ();
      ARCH_SETUP_TLS ();
      ARCH_APPLY_IREL ();
    
    __ehdr_start may require RELATIVE relocation so it was moved
    after relocation processing but before tls setup which needs
    the program headers. This also means that targets that need
    ifunc resolution to be after tls setup cannot support static
    pie without splitting RELATIVE and IRELATIVE processing (or
    removing some of the dependencies between these steps).
    
    Fixes bug 27072.

Diff:
---
 csu/libc-start.c | 30 ++++++++++++++++++------------
 1 file changed, 18 insertions(+), 12 deletions(-)

diff --git a/csu/libc-start.c b/csu/libc-start.c
index 1e90dcb0a7..3239125202 100644
--- a/csu/libc-start.c
+++ b/csu/libc-start.c
@@ -146,8 +146,6 @@ LIBC_START_MAIN (int (*main) (int, char **, char ** MAIN_AUXVEC_DECL),
   int result;
 
 #ifndef SHARED
-  _dl_relocate_static_pie ();
-
   char **ev = &argv[argc + 1];
 
   __environ = ev;
@@ -169,6 +167,24 @@ LIBC_START_MAIN (int (*main) (int, char **, char ** MAIN_AUXVEC_DECL),
   }
 #  endif
   _dl_aux_init (auxvec);
+# endif
+
+  /* Initialize very early so that tunables can use it.  */
+  __libc_init_secure ();
+
+  __tunables_init (__environ);
+
+  ARCH_INIT_CPU_FEATURES ();
+
+  /* Do static pie self relocation after tunables and cpu features
+     are setup for ifunc resolvers. Before this point relocations
+     must be avoided.  */
+  _dl_relocate_static_pie ();
+
+  /* Perform IREL{,A} relocations.  */
+  ARCH_SETUP_IREL ();
+
+# ifdef HAVE_AUX_VECTOR
   if (GL(dl_phdr) == NULL)
 # endif
     {
@@ -188,16 +204,6 @@ LIBC_START_MAIN (int (*main) (int, char **, char ** MAIN_AUXVEC_DECL),
         }
     }
 
-  /* Initialize very early so that tunables can use it.  */
-  __libc_init_secure ();
-
-  __tunables_init (__environ);
-
-  ARCH_INIT_CPU_FEATURES ();
-
-  /* Perform IREL{,A} relocations.  */
-  ARCH_SETUP_IREL ();
-
   /* The stack guard goes into the TCB, so initialize it early.  */
   ARCH_SETUP_TLS ();