From de7a7c04a92dbc5d35cb37e47c471e12784cc95e Mon Sep 17 00:00:00 2001
From: Khem Raj <raj.khem@gmail.com>
Date: Wed, 18 Mar 2015 00:20:09 +0000
Subject: [PATCH 11/29] Quote from bug 1443 which explains what the patch does
 :

  We build some random program and link it with -lust.  When we run it,
  it dies with a SIGSEGV before reaching main().

  Libust.so depends on liburcu-bp.so from the usermode-rcu package.
  Although libust.so is not prelinked, liburcu-bp.so IS prelinked; this
  is critical.

  Libust.so uses a TLS / __thread variable that is defined in liburcu-
  bp.so.  There are special ARM-specific relocation types that allow two
  shared libraries to share thread-specific data.  This is critical too.

  One more critical issue: although liburcu-bp.so is prelinked, we can't
  load it at its prelinked address, because we also link against
  librt.so, and librt.so uses that address.

  The dynamic linker is forced to relink liburcu-bp.so at a different
  address.  In the course of relinking, it processes the special ARM
  relocation record mentioned above.  The prelinker has already filled
  in the information, which is a short offset into a table of thread-
  specific data that is allocated per-thread for each library that uses
  TLS.  Because the normal behavior of a relocation is to add the symbol
  value to an addend stored at the address being relocated, we end up
  adding the short offset to itself, doubling it.

  Now we have an awkward situation.  The libust.so library doesn't know
  about the addend, so its TLS data for this element is correct.  The
  liburcu-bp.so library has a different offset for the element.  When we
  go to initialize the element for the first time in liburcu-bp.so, we
  write the address of the result at the doubled (broken) offset.
  Later, when we refer to the address from libust.so, we check the value
  at the correct offset, but it's NULL, so we eat hot SIGSEGV.

Upstream-Status: Pending

Signed-off-by: Andrei Dinu <andrei.adrianx.dinu@intel.com>
Signed-off-by: Khem Raj <raj.khem@gmail.com>
---
 sysdeps/arm/dl-machine.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sysdeps/arm/dl-machine.h b/sysdeps/arm/dl-machine.h
index 90856779b1..a29bb86c56 100644
--- a/sysdeps/arm/dl-machine.h
+++ b/sysdeps/arm/dl-machine.h
@@ -510,7 +510,7 @@ elf_machine_rel (struct link_map *map, const Elf32_Rel *reloc,
 
 	case R_ARM_TLS_DTPOFF32:
 	  if (sym != NULL)
-	    *reloc_addr += sym->st_value;
+	    *reloc_addr = sym->st_value;
 	  break;
 
 	case R_ARM_TLS_TPOFF32:
-- 
2.27.0