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rseq/selftests: Use __rseq_handled symbol to coexist with glibc

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In order to integrate rseq into user-space applications, expose a
__rseq_handled symbol so many rseq users can be linked into the same
application (e.g. librseq and glibc).

The __rseq_refcount TLS variable is static to the librseq library. It
ensures that rseq syscall registration/unregistration happens only for
the most early/late caller to rseq_{,un}register_current_thread for each
thread, thus ensuring that rseq is registered across the lifetime of all
rseq users for a given thread.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
CC: Shuah Khan <shuah@kernel.org>
CC: Carlos O'Donell <carlos@redhat.com>
CC: Florian Weimer <fweimer@redhat.com>
CC: Joseph Myers <joseph@codesourcery.com>
CC: Szabolcs Nagy <szabolcs.nagy@arm.com>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: Ben Maurer <bmaurer@fb.com>
CC: Peter Zijlstra <peterz@infradead.org>
CC: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
CC: Boqun Feng <boqun.feng@gmail.com>
CC: Will Deacon <will.deacon@arm.com>
CC: Dave Watson <davejwatson@fb.com>
CC: Paul Turner <pjt@google.com>
CC: linux-api@vger.kernel.org
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
This commit is contained in:
Mathieu Desnoyers 2019-04-29 11:27:55 -04:00 committed by Shuah Khan
parent a3e3131f94
commit 5b0c308a05
2 changed files with 48 additions and 8 deletions
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55
tools/testing/selftests/rseq/rseq.c
View File

@ -25,18 +25,27 @@
#include <syscall.h>
#include <assert.h>
#include <signal.h>
#include <limits.h>
#include "rseq.h"
#define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]))
__attribute__((tls_model("initial-exec"))) __thread
volatile struct rseq __rseq_abi = {
__thread volatile struct rseq __rseq_abi = {
.cpu_id = RSEQ_CPU_ID_UNINITIALIZED,
};
static __attribute__((tls_model("initial-exec"))) __thread
volatile int refcount;
/*
* Shared with other libraries. This library may take rseq ownership if it is
* still 0 when executing the library constructor. Set to 1 by library
* constructor when handling rseq. Set to 0 in destructor if handling rseq.
*/
int __rseq_handled;
/* Whether this library have ownership of rseq registration. */
static int rseq_ownership;
static __thread volatile uint32_t __rseq_refcount;
static void signal_off_save(sigset_t *oldset)
{
@ -69,8 +78,14 @@ int rseq_register_current_thread(void)
int rc, ret = 0;
sigset_t oldset;
if (!rseq_ownership)
return 0;
signal_off_save(&oldset);
if (refcount++)
if (__rseq_refcount == UINT_MAX) {
ret = -1;
goto end;
}
if (__rseq_refcount++)
goto end;
rc = sys_rseq(&__rseq_abi, sizeof(struct rseq), 0, RSEQ_SIG);
if (!rc) {
@ -78,9 +93,9 @@ int rseq_register_current_thread(void)
goto end;
}
if (errno != EBUSY)
__rseq_abi.cpu_id = -2;
__rseq_abi.cpu_id = RSEQ_CPU_ID_REGISTRATION_FAILED;
ret = -1;
refcount--;
__rseq_refcount--;
end:
signal_restore(oldset);
return ret;
@ -91,13 +106,20 @@ int rseq_unregister_current_thread(void)
int rc, ret = 0;
sigset_t oldset;
if (!rseq_ownership)
return 0;
signal_off_save(&oldset);
if (--refcount)
if (!__rseq_refcount) {
ret = -1;
goto end;
}
if (--__rseq_refcount)
goto end;
rc = sys_rseq(&__rseq_abi, sizeof(struct rseq),
RSEQ_FLAG_UNREGISTER, RSEQ_SIG);
if (!rc)
goto end;
__rseq_refcount = 1;
ret = -1;
end:
signal_restore(oldset);
@ -115,3 +137,20 @@ int32_t rseq_fallback_current_cpu(void)
}
return cpu;
}
void __attribute__((constructor)) rseq_init(void)
{
/* Check whether rseq is handled by another library. */
if (__rseq_handled)
return;
__rseq_handled = 1;
rseq_ownership = 1;
}
void __attribute__((destructor)) rseq_fini(void)
{
if (!rseq_ownership)
return;
__rseq_handled = 0;
rseq_ownership = 0;
}

1
tools/testing/selftests/rseq/rseq.h
View File

@ -44,6 +44,7 @@
#endif
extern __thread volatile struct rseq __rseq_abi;
extern int __rseq_handled;
#define rseq_likely(x) __builtin_expect(!!(x), 1)
#define rseq_unlikely(x) __builtin_expect(!!(x), 0)