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018f0fc3b8
It turns out that quite a few applications use bundled mallocs that have been built to use global-dynamic TLS (instead of the recommended initial-exec TLS). The previous workaround from commitafe42e935b("elf: Avoid some free (NULL) calls in _dl_update_slotinfo") does not fix all encountered cases unfortunatelly. This change avoids the TLS generation update for recursive use of TLS from a malloc that was called during a TLS update. This is possible because an interposed malloc has a fixed module ID and TLS slot. (It cannot be unloaded.) If an initially-loaded module ID is encountered in __tls_get_addr and the dynamic linker is already in the middle of a TLS update, use the outdated DTV, thus avoiding another call into malloc. It's still necessary to update the DTV to the most recent generation, to get out of the slow path, which is why the check for recursion is needed. The bookkeeping is done using a global counter instead of per-thread flag because TLS access in the dynamic linker is tricky. All this will go away once the dynamic linker stops using malloc for TLS, likely as part of a change that pre-allocates all TLS during pthread_create/dlopen. Fixes commitd2123d6827("elf: Fix slow tls access after dlopen [BZ #19924]"). Reviewed-by: Szabolcs Nagy <szabolcs.nagy@arm.com>
61 lines
2.0 KiB
C
61 lines
2.0 KiB
C
/* Test with interposed malloc with dynamic TLS.
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Copyright (C) 2024 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <array_length.h>
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#include <stdio.h>
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#include <support/check.h>
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#include <support/xdlfcn.h>
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/* Defined in tst-recursive-tlsmallocmod.so. */
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extern __thread unsigned int malloc_subsytem_counter;
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static int
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do_test (void)
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{
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/* 16 is large enough to exercise the DTV resizing case. */
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void *handles[16];
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for (unsigned int i = 0; i < array_length (handles); ++i)
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{
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/* Re-use the TLS slot for module 0. */
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if (i > 0)
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xdlclose (handles[0]);
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char soname[30];
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snprintf (soname, sizeof (soname), "tst-recursive-tlsmod%u.so", i);
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handles[i] = xdlopen (soname, RTLD_NOW);
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if (i > 0)
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{
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handles[0] = xdlopen ("tst-recursive-tlsmod0.so", RTLD_NOW);
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int (*fptr) (void) = xdlsym (handles[0], "get_threadvar_0");
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/* May trigger TLS storage allocation using malloc. */
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TEST_COMPARE (fptr (), 0);
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}
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}
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for (unsigned int i = 0; i < array_length (handles); ++i)
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xdlclose (handles[i]);
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printf ("info: malloc subsystem calls: %u\n", malloc_subsytem_counter);
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TEST_VERIFY (malloc_subsytem_counter > 0);
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return 0;
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}
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#include <support/test-driver.c>
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