[PATCH v2 02/13] elf, nptl: Resolve recursive lock implementation early
Florian Weimer
fweimer@redhat.com
Thu May 6 18:09:58 GMT 2021
If libpthread is included in libc, it is not necessary to delay
initialization of the lock/unlock function pointers until libpthread
is loaded. This eliminates two unprotected function pointers
from _rtld_global and removes some initialization code from
libpthread.
---
v2: Rename dl-lock.c into dl-mutex.c and use a sysdeps override instead
of a preprocessor conditional.
elf/Makefile | 3 ++-
elf/dl-mutex.c | 19 ++++++++++++++
elf/rtld.c | 18 +++++++++++++
nptl/nptl-init.c | 9 -------
sysdeps/generic/ldsodefs.h | 25 +++++++++++++++++-
sysdeps/nptl/dl-mutex.c | 53 ++++++++++++++++++++++++++++++++++++++
sysdeps/nptl/libc-lockP.h | 17 +++---------
7 files changed, 120 insertions(+), 24 deletions(-)
create mode 100644 elf/dl-mutex.c
create mode 100644 sysdeps/nptl/dl-mutex.c
diff --git a/elf/Makefile b/elf/Makefile
index 4f99af626f..d3e909637a 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -66,7 +66,8 @@ elide-routines.os = $(all-dl-routines) dl-support enbl-secure dl-origin \
# interpreter and operating independent of libc.
rtld-routines = rtld $(all-dl-routines) dl-sysdep dl-environ dl-minimal \
dl-error-minimal dl-conflict dl-hwcaps dl-hwcaps_split dl-hwcaps-subdirs \
- dl-usage dl-diagnostics dl-diagnostics-kernel dl-diagnostics-cpu
+ dl-usage dl-diagnostics dl-diagnostics-kernel dl-diagnostics-cpu \
+ dl-mutex
all-rtld-routines = $(rtld-routines) $(sysdep-rtld-routines)
CFLAGS-dl-runtime.c += -fexceptions -fasynchronous-unwind-tables
diff --git a/elf/dl-mutex.c b/elf/dl-mutex.c
new file mode 100644
index 0000000000..2cd9d49c2e
--- /dev/null
+++ b/elf/dl-mutex.c
@@ -0,0 +1,19 @@
+/* Recursive locking implementation for the dynamic loader. Generic version.
+ Copyright (C) 2021 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/>. */
+
+/* The generic version initialization happpens in dl_main. */
diff --git a/elf/rtld.c b/elf/rtld.c
index ad325d4c10..a359167f8a 100644
--- a/elf/rtld.c
+++ b/elf/rtld.c
@@ -857,6 +857,14 @@ rtld_lock_default_unlock_recursive (void *lock)
__rtld_lock_default_unlock_recursive (lock);
}
#endif
+#if PTHREAD_IN_LIBC
+/* Dummy implementation. See __rtld_mutex_init. */
+static int
+rtld_mutex_dummy (pthread_mutex_t *lock)
+{
+ return 0;
+}
+#endif
static void
@@ -1148,6 +1156,10 @@ dl_main (const ElfW(Phdr) *phdr,
GL(dl_rtld_lock_recursive) = rtld_lock_default_lock_recursive;
GL(dl_rtld_unlock_recursive) = rtld_lock_default_unlock_recursive;
#endif
+#if PTHREAD_IN_LIBC
+ ___rtld_mutex_lock = rtld_mutex_dummy;
+ ___rtld_mutex_unlock = rtld_mutex_dummy;
+#endif
/* The explicit initialization here is cheaper than processing the reloc
in the _rtld_local definition's initializer. */
@@ -2363,6 +2375,9 @@ dl_main (const ElfW(Phdr) *phdr,
loader. */
__rtld_malloc_init_real (main_map);
+ /* Likewise for the locking implementation. */
+ __rtld_mutex_init ();
+
/* Mark all the objects so we know they have been already relocated. */
for (struct link_map *l = main_map; l != NULL; l = l->l_next)
{
@@ -2468,6 +2483,9 @@ dl_main (const ElfW(Phdr) *phdr,
at this point. */
__rtld_malloc_init_real (main_map);
+ /* Likewise for the locking implementation. */
+ __rtld_mutex_init ();
+
RTLD_TIMING_VAR (start);
rtld_timer_start (&start);
diff --git a/nptl/nptl-init.c b/nptl/nptl-init.c
index fcab5a0904..2724770533 100644
--- a/nptl/nptl-init.c
+++ b/nptl/nptl-init.c
@@ -179,15 +179,6 @@ __pthread_initialize_minimal_internal (void)
lll_unlock (__default_pthread_attr_lock, LLL_PRIVATE);
#ifdef SHARED
- /* Make __rtld_lock_{,un}lock_recursive use pthread_mutex_{,un}lock,
- keep the lock count from the ld.so implementation. */
- GL(dl_rtld_lock_recursive) = (void *) __pthread_mutex_lock;
- GL(dl_rtld_unlock_recursive) = (void *) __pthread_mutex_unlock;
- unsigned int rtld_lock_count = GL(dl_load_lock).mutex.__data.__count;
- GL(dl_load_lock).mutex.__data.__count = 0;
- while (rtld_lock_count-- > 0)
- __pthread_mutex_lock (&GL(dl_load_lock).mutex);
-
GL(dl_make_stack_executable_hook) = &__make_stacks_executable;
#endif
diff --git a/sysdeps/generic/ldsodefs.h b/sysdeps/generic/ldsodefs.h
index 1b064c5894..6d590d1335 100644
--- a/sysdeps/generic/ldsodefs.h
+++ b/sysdeps/generic/ldsodefs.h
@@ -403,7 +403,7 @@ struct rtld_global
struct auditstate _dl_rtld_auditstate[DL_NNS];
#endif
-#if defined SHARED && defined _LIBC_REENTRANT \
+#if !PTHREAD_IN_LIBC && defined SHARED \
&& defined __rtld_lock_default_lock_recursive
EXTERN void (*_dl_rtld_lock_recursive) (void *);
EXTERN void (*_dl_rtld_unlock_recursive) (void *);
@@ -1318,6 +1318,29 @@ link_map_audit_state (struct link_map *l, size_t index)
}
#endif /* SHARED */
+#if PTHREAD_IN_LIBC && defined SHARED
+/* Recursive locking implementation for use within the dynamic loader.
+ Used to define the __rtld_lock_lock_recursive and
+ __rtld_lock_unlock_recursive via <libc-lock.h>. Initialized to a
+ no-op dummy implementation early. Similar
+ to GL (dl_rtld_lock_recursive) and GL (dl_rtld_unlock_recursive)
+ in !PTHREAD_IN_LIBC builds. */
+extern int (*___rtld_mutex_lock) (pthread_mutex_t *) attribute_hidden;
+extern int (*___rtld_mutex_unlock) (pthread_mutex_t *lock) attribute_hidden;
+
+/* Called after libc has been loaded, but before RELRO is activated.
+ Used to initialize the function pointers to the actual
+ implementations. */
+void __rtld_mutex_init (void) attribute_hidden;
+#else /* !PTHREAD_IN_LIBC */
+static inline void
+__rtld_mutex_init (void)
+{
+ /* The initialization happens later (!PTHREAD_IN_LIBC) or is not
+ needed at all (!SHARED). */
+}
+#endif /* !PTHREAD_IN_LIBC */
+
#if THREAD_GSCOPE_IN_TCB
void __thread_gscope_wait (void) attribute_hidden;
# define THREAD_GSCOPE_WAIT() __thread_gscope_wait ()
diff --git a/sysdeps/nptl/dl-mutex.c b/sysdeps/nptl/dl-mutex.c
new file mode 100644
index 0000000000..08b71dc21b
--- /dev/null
+++ b/sysdeps/nptl/dl-mutex.c
@@ -0,0 +1,53 @@
+/* Recursive locking implementation for the dynamic loader. NPTL version.
+ Copyright (C) 2021 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/>. */
+
+/* Use the mutex implementation in libc (assuming PTHREAD_IN_LIBC). */
+
+#include <assert.h>
+#include <first-versions.h>
+#include <ldsodefs.h>
+
+__typeof (pthread_mutex_lock) *___rtld_mutex_lock attribute_relro;
+__typeof (pthread_mutex_unlock) *___rtld_mutex_unlock attribute_relro;
+
+void
+__rtld_mutex_init (void)
+{
+ /* There is an implicit assumption here that the lock counters are
+ zero and this function is called while nothing is locked. For
+ early initialization of the mutex functions this is true because
+ it happens directly in dl_main in elf/rtld.c, and not some ELF
+ constructor while holding loader locks. */
+
+ struct link_map *libc_map = GL (dl_ns)[LM_ID_BASE].libc_map;
+
+ const ElfW(Sym) *sym
+ = _dl_lookup_direct (libc_map, "pthread_mutex_lock",
+ 0x4f152227, /* dl_new_hash output. */
+ FIRST_VERSION_libc_pthread_mutex_lock_STRING,
+ FIRST_VERSION_libc_pthread_mutex_lock_HASH);
+ assert (sym != NULL);
+ ___rtld_mutex_lock = DL_SYMBOL_ADDRESS (libc_map, sym);
+
+ sym = _dl_lookup_direct (libc_map, "pthread_mutex_unlock",
+ 0x7dd7aaaa, /* dl_new_hash output. */
+ FIRST_VERSION_libc_pthread_mutex_unlock_STRING,
+ FIRST_VERSION_libc_pthread_mutex_unlock_HASH);
+ assert (sym != NULL);
+ ___rtld_mutex_unlock = DL_SYMBOL_ADDRESS (libc_map, sym);
+}
diff --git a/sysdeps/nptl/libc-lockP.h b/sysdeps/nptl/libc-lockP.h
index ae9691d40e..ec7b02bbdd 100644
--- a/sysdeps/nptl/libc-lockP.h
+++ b/sysdeps/nptl/libc-lockP.h
@@ -151,9 +151,6 @@ _Static_assert (LLL_LOCK_INITIALIZER == 0, "LLL_LOCK_INITIALIZER != 0");
__libc_maybe_call (__pthread_mutex_trylock, (&(NAME)), 0)
#endif
-#define __rtld_lock_trylock_recursive(NAME) \
- __libc_maybe_call (__pthread_mutex_trylock, (&(NAME).mutex), 0)
-
/* Unlock the named lock variable. */
#if IS_IN (libc) || IS_IN (libpthread)
# define __libc_lock_unlock(NAME) \
@@ -163,19 +160,13 @@ _Static_assert (LLL_LOCK_INITIALIZER == 0, "LLL_LOCK_INITIALIZER != 0");
#endif
#define __libc_rwlock_unlock(NAME) __pthread_rwlock_unlock (&(NAME))
-#ifdef SHARED
-# define __rtld_lock_default_lock_recursive(lock) \
- ++((pthread_mutex_t *)(lock))->__data.__count;
-
-# define __rtld_lock_default_unlock_recursive(lock) \
- --((pthread_mutex_t *)(lock))->__data.__count;
-
+#if IS_IN (rtld)
# define __rtld_lock_lock_recursive(NAME) \
- GL(dl_rtld_lock_recursive) (&(NAME).mutex)
+ ___rtld_mutex_lock (&(NAME).mutex)
# define __rtld_lock_unlock_recursive(NAME) \
- GL(dl_rtld_unlock_recursive) (&(NAME).mutex)
-#else
+ ___rtld_mutex_unlock (&(NAME).mutex)
+#else /* Not in the dynamic loader. */
# define __rtld_lock_lock_recursive(NAME) \
__pthread_mutex_lock (&(NAME).mutex)
--
2.30.2
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