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Linux: Make __rseq_size useful for feature detection (bug 31965)
The __rseq_size value is now the active area of struct rseq (so 20 initially), not the full struct size including padding at the end (32 initially). Update misc/tst-rseq to print some additional diagnostics. Reviewed-by: Michael Jeanson <mjeanson@efficios.com> Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
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@ -49,6 +49,9 @@ Deprecated and removed features, and other changes affecting compatibility:
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<utmpx.h> (except for login_tty) due to locking and session management
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problems.
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* __rseq_size now denotes the size of the active rseq area (20 bytes
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initially), not the size of struct rseq (32 bytes initially).
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Changes to build and runtime requirements:
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[Add changes to build and runtime requirements here]
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@ -1007,8 +1007,12 @@ This variable is either zero (if restartable sequence registration
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failed or has been disabled) or the size of the restartable sequence
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registration. This can be different from the size of @code{struct rseq}
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if the kernel has extended the size of the registration. If
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registration is successful, @code{__rseq_size} is at least 32 (the
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initial size of @code{struct rseq}).
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registration is successful, @code{__rseq_size} is at least 20 (the
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initially active size of @code{struct rseq}).
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Previous versions of @theglibc{} set this to 32 even if the kernel only
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supported the initial area of 20 bytes because the value included unused
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padding at the end of the restartable sequence area.
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@end deftypevar
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@deftypevar {unsigned int} __rseq_flags
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@ -46,10 +46,6 @@ rtld_mutex_dummy (pthread_mutex_t *lock)
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const unsigned int __rseq_flags;
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/* The variables are in .data.relro but are not yet write-protected. */
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extern unsigned int _rseq_size attribute_hidden;
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extern ptrdiff_t _rseq_offset attribute_hidden;
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void
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__tls_pre_init_tp (void)
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{
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@ -106,9 +102,7 @@ __tls_init_tp (void)
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bool do_rseq = true;
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do_rseq = TUNABLE_GET (rseq, int, NULL);
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if (rseq_register_current_thread (pd, do_rseq))
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{
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_rseq_size = sizeof (pd->rseq_area);
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}
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_rseq_size = RSEQ_AREA_SIZE_INITIAL_USED;
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#ifdef RSEQ_SIG
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/* This should be a compile-time constant, but the current
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@ -25,15 +25,34 @@
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#include <stdio.h>
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#include <sys/rseq.h>
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/* 32 is the initially required value for the area size. The
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actually used rseq size may be less (20 bytes initially). */
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#define RSEQ_AREA_SIZE_INITIAL 32
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#define RSEQ_AREA_SIZE_INITIAL_USED 20
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/* The variables are in .data.relro but are not yet write-protected. */
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extern unsigned int _rseq_size attribute_hidden;
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extern ptrdiff_t _rseq_offset attribute_hidden;
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#ifdef RSEQ_SIG
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static inline bool
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rseq_register_current_thread (struct pthread *self, bool do_rseq)
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{
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if (do_rseq)
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{
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unsigned int size;
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#if IS_IN (rtld)
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/* Use the hidden symbol in ld.so. */
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size = _rseq_size;
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#else
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size = __rseq_size;
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#endif
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if (size < RSEQ_AREA_SIZE_INITIAL)
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/* The initial implementation used only 20 bytes out of 32,
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but still expected size 32. */
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size = RSEQ_AREA_SIZE_INITIAL;
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int ret = INTERNAL_SYSCALL_CALL (rseq, &self->rseq_area,
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sizeof (self->rseq_area),
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0, RSEQ_SIG);
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size, 0, RSEQ_SIG);
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if (!INTERNAL_SYSCALL_ERROR_P (ret))
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return true;
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}
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@ -29,6 +29,7 @@
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# include <stdlib.h>
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# include <string.h>
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# include <syscall.h>
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# include <sys/auxv.h>
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# include <thread_pointer.h>
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# include <tls.h>
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# include "tst-rseq.h"
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@ -42,7 +43,8 @@ do_rseq_main_test (void)
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TEST_COMPARE (__rseq_flags, 0);
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TEST_VERIFY ((char *) __thread_pointer () + __rseq_offset
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== (char *) &pd->rseq_area);
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TEST_COMPARE (__rseq_size, sizeof (pd->rseq_area));
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/* The current implementation only supports the initial size. */
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TEST_COMPARE (__rseq_size, 20);
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}
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static void
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@ -52,6 +54,12 @@ do_rseq_test (void)
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{
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FAIL_UNSUPPORTED ("kernel does not support rseq, skipping test");
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}
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printf ("info: __rseq_size: %u\n", __rseq_size);
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printf ("info: __rseq_offset: %td\n", __rseq_offset);
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printf ("info: __rseq_flags: %u\n", __rseq_flags);
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printf ("info: getauxval (AT_RSEQ_FEATURE_SIZE): %ld\n",
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getauxval (AT_RSEQ_FEATURE_SIZE));
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printf ("info: getauxval (AT_RSEQ_ALIGN): %ld\n", getauxval (AT_RSEQ_ALIGN));
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do_rseq_main_test ();
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}
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#else /* RSEQ_SIG */
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