elf: Change TLS static surplus default back to 1664

Make the computation in elf/dl-tls.c more transparent, and add
an explicit test for the historic value.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>

1 files changed, 30 insertions, 7 deletions

diff --git a/elf/dl-tls.c b/elf/dl-tls.c
index 9a17427..9fa62f5 100644
--- a/elf/dl-tls.c
+++ b/elf/dl-tls.c
@@ -54,13 +54,37 @@
    Audit modules use their own namespaces, they are not included in rtld.nns,
    but come on top when computing the number of namespaces.  */
 
-/* Size of initial-exec TLS in libc.so.  */
-#define LIBC_IE_TLS 160
+/* Size of initial-exec TLS in libc.so.  This should be the maximum of
+   observed PT_GNU_TLS sizes across all architectures.  Some
+   architectures have lower values due to differences in type sizes
+   and link editor capabilities.  */
+#define LIBC_IE_TLS 144
+
 /* Size of initial-exec TLS in libraries other than libc.so.
    This should be large enough to cover runtime libraries of the
    compiler such as libgomp and libraries in libc other than libc.so.  */
 #define OTHER_IE_TLS 144
 
+/* Default number of namespaces.  */
+#define DEFAULT_NNS 4
+
+/* Default for dl_tls_static_optional.  */
+#define OPTIONAL_TLS 512
+
+/* Compute the static TLS surplus based on the namespace count and the
+   TLS space that can be used for optimizations.  */
+static inline int
+tls_static_surplus (int nns, int opt_tls)
+{
+  return (nns - 1) * LIBC_IE_TLS + nns * OTHER_IE_TLS + opt_tls;
+}
+
+/* This value is chosen so that with default values for the tunables,
+   the computation of dl_tls_static_surplus in
+   _dl_tls_static_surplus_init yields the historic value 1664, for
+   backwards compatibility.  */
+#define LEGACY_TLS (1664 - tls_static_surplus (DEFAULT_NNS, OPTIONAL_TLS))
+
 /* Calculate the size of the static TLS surplus, when the given
    number of audit modules are loaded.  Must be called after the
    number of audit modules is known and before static TLS allocation.  */
@@ -74,8 +98,8 @@ _dl_tls_static_surplus_init (size_t naudit)
   opt_tls = TUNABLE_GET (optional_static_tls, size_t, NULL);
 #else
   /* Default values of the tunables.  */
-  nns = 4;
-  opt_tls = 512;
+  nns = DEFAULT_NNS;
+  opt_tls = OPTIONAL_TLS;
 #endif
   if (nns > DL_NNS)
     nns = DL_NNS;
@@ -85,9 +109,8 @@ _dl_tls_static_surplus_init (size_t naudit)
   nns += naudit;
 
   GL(dl_tls_static_optional) = opt_tls;
-  GLRO(dl_tls_static_surplus) = ((nns - 1) * LIBC_IE_TLS
-				 + nns * OTHER_IE_TLS
-				 + opt_tls);
+  assert (LEGACY_TLS >= 0);
+  GLRO(dl_tls_static_surplus) = tls_static_surplus (nns, opt_tls) + LEGACY_TLS;
 }
 
 /* Out-of-memory handler.  */