[PATCH 3/4] elf: Use TLS_DTV_OFFSET in __tls_get_addr

[Florian Weimer]

This fixes commit 5e249192cac7354af02a7347a0d8c984e0c88ed3 ("elf:
Remove the GET_ADDR_ARGS and related macros from the TLS code"):
GET_ADDR_ARGS was indeed unused, but GET_ADDR_OFFSET was used
on several targets, those that define TLS_DTV_OFFSET.  Instead
of reintroducing GET_ADDR_OFFSET, use TLS_DTV_OFFSET directly,
now that it is defined on all targets.

In the new tls_get_addr_adjust helper function, add a cast to
uintptr_t to help the s390 case, where the offset can be positive or
negative, depending on the addresses malloc returns.  The cast avoids
pointer wraparound/overflow.  The outer uintptr_t cast is needed
to suppress a warning on x86-64 x32 about mismatched integer/pointer
sizes.

Eventually this offset should be folded into the DTV addresses
themselves, to eliminate the subtraction on the TLS fast path.
This will require an adjustment to libthread_db because the
debugger interface currently returns unadjusted pointers.
---
 elf/dl-tls.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/elf/dl-tls.c b/elf/dl-tls.c
index 4df83b9bb2..5f3c03edf8 100644
--- a/elf/dl-tls.c
+++ b/elf/dl-tls.c
@@ -890,6 +890,14 @@ _dl_update_slotinfo (unsigned long int req_modid, size_t new_gen)
   return the_map;
 }
 
+/* Adjust the TLS variable pointer using the TLS descriptor offset and
+   the ABI-specific offset.  */
+static inline void *
+tls_get_addr_adjust (void *from_dtv, tls_index *ti)
+{
+  return (void *) (uintptr_t) ((uintptr_t) from_dtv + ti->ti_offset
+			       + TLS_DTV_OFFSET);
+}
 
 static void *
 __attribute_noinline__
@@ -939,7 +947,7 @@ tls_get_addr_tail (tls_index *ti, dtv_t *dtv, struct link_map *the_map)
 	  dtv[ti->ti_module].pointer.to_free = NULL;
 	  dtv[ti->ti_module].pointer.val = p;
 
-	  return (char *) p + ti->ti_offset;
+	  return tls_get_addr_adjust (p, ti);
 	}
       else
 	__rtld_lock_unlock_recursive (GL(dl_load_tls_lock));
@@ -948,7 +956,7 @@ tls_get_addr_tail (tls_index *ti, dtv_t *dtv, struct link_map *the_map)
   dtv[ti->ti_module].pointer = result;
   assert (result.to_free != NULL);
 
-  return (char *) result.val + ti->ti_offset;
+  return tls_get_addr_adjust (result.val, ti);
 }
 
 
@@ -964,7 +972,7 @@ update_get_addr (tls_index *ti, size_t gen)
   if (__glibc_unlikely (p == TLS_DTV_UNALLOCATED))
     return tls_get_addr_tail (ti, dtv, the_map);
 
-  return (void *) p + ti->ti_offset;
+  return tls_get_addr_adjust (p, ti);
 }
 
 /* For all machines that have a non-macro version of __tls_get_addr, we
@@ -1015,7 +1023,7 @@ __tls_get_addr (tls_index *ti)
   if (__glibc_unlikely (p == TLS_DTV_UNALLOCATED))
     return tls_get_addr_tail (ti, dtv, NULL);
 
-  return (char *) p + ti->ti_offset;
+  return tls_get_addr_adjust (p, ti);
 }
 #endif /* SHARED */
 
-- 
2.47.1