Add generic 'extra TLS'

Add the logic to append an 'extra TLS' block in the TLS block allocator
with a generic stub implementation. The duplicated code in
'csu/libc-tls.c' and 'elf/dl-tls.c' is to handle both statically linked
applications and the ELF dynamic loader.

Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Reviewed-by: Florian Weimer <fweimer@redhat.com>

1 files changed, 72 insertions, 0 deletions

diff --git a/elf/dl-tls.c b/elf/dl-tls.c
index c2d1726..45ea058 100644
--- a/elf/dl-tls.c
+++ b/elf/dl-tls.c
@@ -36,6 +36,8 @@
 #define TUNABLE_NAMESPACE rtld
 #include <dl-tunables.h>
 
+#include <dl-extra_tls.h>
+
 /* Surplus static TLS, GLRO(dl_tls_static_surplus), is used for
 
    - IE TLS in libc.so for all dlmopen namespaces except in the initial
@@ -323,6 +325,39 @@ _dl_determine_tlsoffset (void)
       slotinfo[cnt].map->l_tls_offset = off;
     }
 
+  /* Insert the extra TLS block after the last TLS block.  */
+
+  /* Extra TLS block for internal usage to append at the end of the TLS blocks
+     (in allocation order).  The address at which the block is allocated must
+     be aligned to 'extra_tls_align'.  The size of the block as returned by
+     '_dl_extra_tls_get_size ()' is always a multiple of the aligment.
+
+     On Linux systems this is where the rseq area will be allocated.  On other
+     systems it is currently unused and both values will be '0'.  */
+  size_t extra_tls_size = _dl_extra_tls_get_size ();
+  size_t extra_tls_align = _dl_extra_tls_get_align ();
+
+  /* Increase the maximum alignment with the extra TLS alignment requirements
+     if necessary.  */
+  max_align = MAX (max_align, extra_tls_align);
+
+  /* Add the extra TLS block to the global offset.  To ensure proper alignment,
+     first align the current global offset to the extra TLS block requirements
+     and then add the extra TLS block size.  Both values respect the extra TLS
+     alignment requirements and so does the resulting offset.  */
+  offset = roundup (offset, extra_tls_align ?: 1) + extra_tls_size;
+
+ /* Record the extra TLS offset.
+
+    With TLS_TCB_AT_TP the TLS blocks are allocated before the thread pointer
+    in reverse order.  Our block is added last which results in it being the
+    first in the static TLS block, thus record the most negative offset.
+
+    The alignment requirements of the pointer resulting from this offset and
+    the thread pointer are enforced by 'max_align' which is used to align the
+    tcb_offset.  */
+  _dl_extra_tls_set_offset (-offset);
+
   GL(dl_tls_static_used) = offset;
   GLRO (dl_tls_static_size) = (roundup (offset + GLRO(dl_tls_static_surplus),
 					max_align)
@@ -368,6 +403,43 @@ _dl_determine_tlsoffset (void)
       offset = off + slotinfo[cnt].map->l_tls_blocksize - firstbyte;
     }
 
+  /* Insert the extra TLS block after the last TLS block.  */
+
+  /* Extra TLS block for internal usage to append at the end of the TLS blocks
+     (in allocation order).  The address at which the block is allocated must
+     be aligned to 'extra_tls_align'.  The size of the block as returned by
+     '_dl_extra_tls_get_size ()' is always a multiple of the aligment.
+
+     On Linux systems this is where the rseq area will be allocated.  On other
+     systems it is currently unused and both values will be '0'.  */
+  size_t extra_tls_size = _dl_extra_tls_get_size ();
+  size_t extra_tls_align = _dl_extra_tls_get_align ();
+
+  /* Increase the maximum alignment with the extra TLS alignment requirements
+     if necessary.  */
+  max_align = MAX (max_align, extra_tls_align);
+
+  /* Align the global offset to the beginning of the extra TLS block.  */
+  offset = roundup (offset, extra_tls_align ?: 1);
+
+ /* Record the extra TLS offset.
+
+    With TLS_DTV_AT_TP the TLS blocks are allocated after the thread pointer in
+    order.  Our block is added last which results in it being the last in the
+    static TLS block, thus record the offset as the size of the static TLS
+    block minus the size of our block.
+
+    On some architectures the TLS blocks are offset from the thread pointer,
+    include this offset in the extra TLS block offset.
+
+    The alignment requirements of the pointer resulting from this offset and
+    the thread pointer are enforced by 'max_align' which is used to align the
+    tcb_offset.  */
+  _dl_extra_tls_set_offset (offset - TLS_TP_OFFSET);
+
+  /* Add the extra TLS block to the global offset.  */
+  offset += extra_tls_size;
+
   GL(dl_tls_static_used) = offset;
   GLRO (dl_tls_static_size) = roundup (offset + GLRO(dl_tls_static_surplus),
 				       TCB_ALIGNMENT);