Linux: Perform rseq registration at C startup and thread creation

Register rseq TLS for each thread (including main), and unregister for
each thread (excluding main).  "rseq" stands for Restartable Sequences.

See the rseq(2) man page proposed here:
  https://lkml.org/lkml/2018/9/19/647

Those are based on glibc master branch commit 3ee1e0ec5c.
The rseq system call was merged into Linux 4.18.

The TLS_STATIC_SURPLUS define is increased to leave additional room for
dlopen'd initial-exec TLS, which keeps elf/tst-auditmany working.

The increase (76 bytes) is larger than 32 bytes because it has not been
increased in quite a while.  The cost in terms of additional TLS storage
is quite significant, but it will also obscure some initial-exec-related
dlopen failures.

1 files changed, 7 insertions, 1 deletions

diff --git a/elf/dl-tls.c b/elf/dl-tls.c
index fa03234..ca13778 100644
--- a/elf/dl-tls.c
+++ b/elf/dl-tls.c
@@ -31,7 +31,7 @@
 
 /* Amount of excess space to allocate in the static TLS area
    to allow dynamic loading of modules defining IE-model TLS data.  */
-#define TLS_STATIC_SURPLUS	64 + DL_NNS * 100
+#define TLS_STATIC_SURPLUS	64 + DL_NNS * 176
 
 
 /* Out-of-memory handler.  */
@@ -134,6 +134,12 @@ void
 _dl_determine_tlsoffset (void)
 {
   size_t max_align = TLS_TCB_ALIGN;
+  /* libc.so with rseq has TLS with 32-byte alignment.  Since TLS is
+     initialized before audit modules are loaded and slotinfo
+     information is available, this is not taken into account below in
+     the audit case.  */
+  max_align = MAX (max_align, 32U);
+
   size_t freetop = 0;
   size_t freebottom = 0;