Consolidate TLS block allocation for static binaries with ld.so

Use the same code to compute the TLS block size and its alignment.
The code in elf/dl-tls.c is linked in anyway for all binaries
due to the reference to _dl_tls_static_surplus_init.

It is not possible to call _dl_allocate_tls_storage directly
because malloc is not available in the static case.  (The
dynamic linker uses the minimal malloc at this stage.)  Therefore,
split _dl_tls_block_size_with_pre and _dl_tls_block_align from
_dl_allocate_tls_storage, and call those new functions from
__libc_setup_tls.

This fixes extra TLS allocation for the static case, and apparently
some pre-existing bugs as well (the independent recomputation of
TLS block sizes in init_static_tls looks rather suspect).

Fixes commit 0e411c5d3098982d67cd2d7a233eaa6c977a1869 ("Add generic
'extra TLS'").

1 files changed, 70 insertions, 0 deletions

diff --git a/elf/dl-tls_block_align.h b/elf/dl-tls_block_align.h
new file mode 100644
index 0000000000..82016f3bb5
--- /dev/null
+++ b/elf/dl-tls_block_align.h
@@ -0,0 +1,70 @@
+/* Computation of TLS block size and its alignment.
+   Copyright (C) 2002-2025 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+/* Compute the size of the TLS block for memory allocation.  */
+static size_t
+_dl_tls_block_size_with_pre (void)
+{
+  size_t size = GLRO (dl_tls_static_size);
+
+#if TLS_DTV_AT_TP
+  /* Memory layout is:
+     [ TLS_PRE_TCB_SIZE ] [ TLS_TCB_SIZE ] [ TLS blocks ]
+                          ^ This should be returned.  */
+  size += TLS_PRE_TCB_SIZE;
+#endif
+  return size;
+}
+
+/* SIZE must be the value returned by _dl_tls_block_size_with_pre.
+   ALLOCATED must point to at least SIZE + GLRO (dl_tls_static_align)
+   bytes.  */
+static void *
+_dl_tls_block_align (size_t size, void *allocated)
+{
+  void *result;
+  size_t alignment = GLRO (dl_tls_static_align);
+
+#if TLS_TCB_AT_TP
+  /* The TCB follows the TLS blocks, which determine the alignment.
+     (TCB alignment requirements have been taken into account when
+     calculating GLRO (dl_tls_static_align).)  */
+  void *aligned = (void *) roundup ((uintptr_t) allocated, alignment);
+  result = aligned + size - TLS_TCB_SIZE;
+
+  /* Clear the TCB data structure.  We can't ask the caller (i.e.
+     libpthread) to do it, because we will initialize the DTV et al.  */
+  memset (result, '\0', TLS_TCB_SIZE);
+#elif TLS_DTV_AT_TP
+  /* Pre-TCB and TCB come before the TLS blocks.  The layout computed
+     in _dl_determine_tlsoffset assumes that the TCB is aligned to the
+     TLS block alignment, and not just the TLS blocks after it.  This
+     can leave an unused alignment gap between the TCB and the TLS
+     blocks.  */
+  result = (void *) roundup
+    (sizeof (void *) + TLS_PRE_TCB_SIZE + (uintptr_t) allocated,
+     alignment);
+
+  /* Clear the TCB data structure and TLS_PRE_TCB_SIZE bytes before
+     it.  We can't ask the caller (i.e. libpthread) to do it, because
+     we will initialize the DTV et al.  */
+  memset (result - TLS_PRE_TCB_SIZE, '\0', TLS_PRE_TCB_SIZE + TLS_TCB_SIZE);
+#endif
+
+  return result;
+}