S390: Use DT_JUMPREL in prelink undo code.

On s390, the current prelink undo code in elf_machine_lazy_rel()
has the requirement, that the plt stubs use the first got slots
after the 3 reserved ones.

In case of undoing prelink, the plt got slots are reset to the correct
addresses whithin the corresponding plt-stub. Therefore the address
is calculated by the address of the first plt-stub-address which
was written by prelink (see l->l_mach.plt) to got[1] and index of
current relocation multiplied with 32 (=size of one plt slot).
The index was calculated with &current-got-slot - &got[3].

This patch removes the requirement, that the plt-got-slots are
starting at got[3]. The index is now calculated with
&current-reloc - &reloc[0]. The first struct Elf64_Rela is stored
at DT_JMPREL.

This patch is needed to prepare for partial relro support.

Ulrich Weigand suggested this approach to use DT_JMPREL - Thanks.

ChangeLog:

	* sysdeps/s390/linkmap.h (struct link_map_machine):
	Remove member gotplt and add member jmprel.
	* sysdeps/s390/s390-32/dl-machine.h
	(elf_machine_runtime_setup): Setup member jmprel with DT_JMPREL
	instead of gotplt with &got[3].
	(elf_machine_lazy_rel): Calculate address with reloc and jmprel.
	* sysdeps/s390/s390-64/dl-machine.h: Likewise.

4 files changed, 16 insertions, 10 deletions

diff --git a/ChangeLog b/ChangeLog
index 72c5549..4f6357a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
+2016-07-06  Stefan Liebler  <stli@linux.vnet.ibm.com>
+
+	* sysdeps/s390/linkmap.h (struct link_map_machine):
+	Remove member gotplt and add member jmprel.
+	* sysdeps/s390/s390-32/dl-machine.h
+	(elf_machine_runtime_setup): Setup member jmprel with DT_JMPREL
+	instead of gotplt with &got[3].
+	(elf_machine_lazy_rel): Calculate address with reloc and jmprel.
+	* sysdeps/s390/s390-64/dl-machine.h: Likewise.
+
 2016-07-06  John David Anglin  <danglin@gcc.gnu.org>
 
 	* sysdeps/hppa/fpu/libm-test-ulps: Regenerate.
diff --git a/sysdeps/s390/linkmap.h b/sysdeps/s390/linkmap.h
index fc1fba3..283615b 100644
--- a/sysdeps/s390/linkmap.h
+++ b/sysdeps/s390/linkmap.h
@@ -2,12 +2,12 @@
 struct link_map_machine
   {
     Elf64_Addr plt; /* Address of .plt + 0x2e */
-    Elf64_Addr gotplt; /* Address of .got + 0x18 */
+    const Elf64_Rela *jmprel; /* Address of first JMP_SLOT reloc */
   };
 #else
 struct link_map_machine
   {
     Elf32_Addr plt; /* Address of .plt + 0x2c */
-    Elf32_Addr gotplt; /* Address of .got + 0x0c */
+    const Elf32_Rela *jmprel; /* Address of first JMP_SLOT reloc */
   };
 #endif
diff --git a/sysdeps/s390/s390-32/dl-machine.h b/sysdeps/s390/s390-32/dl-machine.h
index ec0ae4a..0a58897 100644
--- a/sysdeps/s390/s390-32/dl-machine.h
+++ b/sysdeps/s390/s390-32/dl-machine.h
@@ -109,7 +109,7 @@ elf_machine_runtime_setup (struct link_map *l, int lazy, int profile)
       if (got[1])
 	{
 	  l->l_mach.plt = got[1] + l->l_addr;
-	  l->l_mach.gotplt = (Elf32_Addr) &got[3];
+	  l->l_mach.jmprel = (const Elf32_Rela *) D_PTR (l, l_info[DT_JMPREL]);
 	}
       got[1] = (Elf32_Addr) l;	/* Identify this shared object.  */
 
@@ -506,9 +506,7 @@ elf_machine_lazy_rel (struct link_map *map,
       if (__builtin_expect (map->l_mach.plt, 0) == 0)
 	*reloc_addr += l_addr;
       else
-	*reloc_addr =
-	  map->l_mach.plt
-	  + (((Elf32_Addr) reloc_addr) - map->l_mach.gotplt) * 8;
+	*reloc_addr = map->l_mach.plt + (reloc - map->l_mach.jmprel) * 32;
     }
   else if (__glibc_likely (r_type == R_390_IRELATIVE))
     {
diff --git a/sysdeps/s390/s390-64/dl-machine.h b/sysdeps/s390/s390-64/dl-machine.h
index 9ee7c92..6e5ee1e 100644
--- a/sysdeps/s390/s390-64/dl-machine.h
+++ b/sysdeps/s390/s390-64/dl-machine.h
@@ -98,7 +98,7 @@ elf_machine_runtime_setup (struct link_map *l, int lazy, int profile)
       if (got[1])
 	{
 	  l->l_mach.plt = got[1] + l->l_addr;
-	  l->l_mach.gotplt = (Elf64_Addr) &got[3];
+	  l->l_mach.jmprel = (const Elf64_Rela *) D_PTR (l, l_info[DT_JMPREL]);
 	}
       got[1] = (Elf64_Addr) l;	/* Identify this shared object.	 */
 
@@ -460,9 +460,7 @@ elf_machine_lazy_rel (struct link_map *map,
       if (__builtin_expect (map->l_mach.plt, 0) == 0)
 	*reloc_addr += l_addr;
       else
-	*reloc_addr =
-	  map->l_mach.plt
-	  + (((Elf64_Addr) reloc_addr) - map->l_mach.gotplt) * 4;
+	*reloc_addr = map->l_mach.plt + (reloc - map->l_mach.jmprel) * 32;
     }
   else if (__glibc_likely (r_type == R_390_IRELATIVE))
     {