@@ -311,6 +311,7 @@ tests-container := \
tst-dl-cache-old-format \
tst-ldconfig-bad-aux-cache \
tst-ldconfig-ld_so_conf-update \
+ tst-tlsalign-tunable \
# tests-container
ifeq (no,$(build-hardcoded-path-in-tests))
@@ -1093,6 +1094,7 @@ modules-names += \
tst-tls22-mod2-gnu2 \
tst-tls23-mod \
tst-tlsalign-lib \
+ tst-tlsalign-tunable-auditmod \
tst-tlsgap-mod0 \
tst-tlsgap-mod1 \
tst-tlsgap-mod2 \
@@ -1846,6 +1848,11 @@ $(objpfx)tst-nodelete-opened.out: $(objpfx)tst-nodelete-opened-lib.so
$(objpfx)tst-tlsalign-extern: $(objpfx)tst-tlsalign-vars.o
$(objpfx)tst-tlsalign-extern-static: $(objpfx)tst-tlsalign-vars.o
+tst-tlsalign-tunable-TUNABLES = glibc.rtld.optional_static_tls_alignment=0x1000
+tst-tlsalign-tunable-TUNABLES += glibc.rtld.optional_static_tls=0x3000
+tst-tlsalign-tunable-ENV = LD_AUDIT=$(objpfx)tst-tlsalign-tunable-auditmod.so
+$(objpfx)tst-tlsalign-tunable.out: $(objpfx)tst-tlsalign-tunable-auditmod.so
+
# The resolver translation unit must always be compiled with
# -fstack-protector-all so the canary code is emitted regardless of the
# default.
@@ -126,6 +126,11 @@ tls_static_surplus (int nns, int opt_tls)
backwards compatibility. */
#define LEGACY_TLS (1664 - tls_static_surplus (DEFAULT_NNS, OPTIONAL_TLS))
+/* This value is set from the glibc.rtld.optional_static_tls_alignment
+ tunable, and sets an additional minimum alignment on the TLS
+ data. */
+static size_t optional_static_tls_alignment = 0;
+
/* 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. */
@@ -136,6 +141,10 @@ _dl_tls_static_surplus_init (size_t naudit)
nns = TUNABLE_GET (nns, size_t, NULL);
opt_tls = TUNABLE_GET (optional_static_tls, size_t, NULL);
+ optional_static_tls_alignment = TUNABLE_GET (optional_static_tls_alignment, size_t, NULL);
+ /* Ignore invalid requests. */
+ if (! powerof2 (optional_static_tls_alignment))
+ optional_static_tls_alignment = 0;
if (nns > DL_NNS)
nns = DL_NNS;
if (DL_NNS - nns < naudit)
@@ -346,6 +355,9 @@ _dl_determine_tlsoffset (void)
size_t extra_tls_size = _dl_extra_tls_get_size ();
size_t extra_tls_align = _dl_extra_tls_get_align ();
+ /* Apply any user-specified alignment, if larger. */
+ extra_tls_align = MAX (extra_tls_align, optional_static_tls_alignment);
+
/* Increase the maximum alignment with the extra TLS alignment requirements
if necessary. */
max_align = MAX (max_align, extra_tls_align);
@@ -426,6 +438,9 @@ _dl_determine_tlsoffset (void)
size_t extra_tls_size = _dl_extra_tls_get_size ();
size_t extra_tls_align = _dl_extra_tls_get_align ();
+ /* Apply any user-specified alignment, if larger. */
+ extra_tls_align = MAX (extra_tls_align, optional_static_tls_alignment);
+
/* Increase the maximum alignment with the extra TLS alignment requirements
if necessary. */
max_align = MAX (max_align, extra_tls_align);
@@ -101,6 +101,11 @@ glibc {
minval: 0
default: 512
}
+ optional_static_tls_alignment {
+ type: SIZE_T
+ minval: 0
+ default: 0
+ }
enable_secure {
type: INT_32
minval: 0
@@ -15,3 +15,4 @@ glibc.rtld.enable_secure: 0 (min: 0, max: 1)
glibc.rtld.execstack: 1 (min: 0, max: 2)
glibc.rtld.nns: 0x4 (min: 0x1, max: 0x10)
glibc.rtld.optional_static_tls: 0x200 (min: 0x0, max: 0x[f]+)
+glibc.rtld.optional_static_tls_alignment: 0x0 (min: 0x0, max: 0x[f]+)
new file mode 100644
@@ -0,0 +1,52 @@
+/* Test for large alignment in TLS blocks, BZ#1838, audit module.
+ Copyright (C) 2020-2026 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/>. */
+
+#include <unistd.h>
+
+__thread int x;
+__thread int b[4]
+ __attribute__ ((tls_model("initial-exec")))
+ __attribute__ ((aligned(0x1000)));
+
+/* These exist just to make the above variables "used". */
+int *
+func_x (void)
+{
+ return &x;
+}
+
+int *
+func_b (void)
+{
+ return b;
+}
+
+void __attribute__ ((constructor))
+la_ctor (void)
+{
+ write (1, "AUDITctor\n", 10);
+ /* We only care if the auditor got loaded. It doesn't need to
+ run. */
+ _exit (0);
+}
+
+unsigned int
+la_version (unsigned int version)
+{
+ return version;
+}
new file mode 100644
@@ -0,0 +1,39 @@
+/* Test for large alignment in TLS blocks, BZ#18383.
+ Copyright (C) 2015-2026 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/>. */
+
+/* This specifically tests that the
+ glibc.rtld.optional_static_tls_alignment tunable works, by loading
+ an audit module that can't load without alignment help. */
+
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+static volatile __thread int tdata1 = 1;
+
+static int
+do_test (void)
+{
+ printf("tst-tlsalign-tunable!\n");
+ /* If the test passes, the auditor itself will call exit with a
+ value of 0. If we get here, we've failed. "Use" tdata1 here
+ too. */
+ return tdata1 ? EXIT_FAILURE : 43;
+}
+
+#include <support/test-driver.c>
@@ -422,6 +422,13 @@ changed once allocated at process startup. The default allocation of
optional static TLS is 512 bytes and is allocated in every thread.
@end deftp
+@deftp Tunable glibc.rtld.optional_static_tls_alignment
+Sets a minimum alignment for the static TLS. The loader normally uses
+the alignment requirements of shared objects, but this might be needed
+for (for example) audit modules that have a higher-than-default
+alignment requirement.
+@end deftp
+
@deftp Tunable glibc.rtld.dynamic_sort
Sets the algorithm to use for DSO sorting, valid values are @samp{1} and
@samp{2}. For value of @samp{1}, an older O(n^3) algorithm is used, which is