Commit 5b0c308a authored by Mathieu Desnoyers's avatar Mathieu Desnoyers Committed by Shuah Khan
Browse files

rseq/selftests: Use __rseq_handled symbol to coexist with glibc 



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: default avatarMathieu 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: default avatarShuah Khan <skhan@linuxfoundation.org>
parent a3e3131f

tools/testing/selftests/rseq/rseq.c

+47 −8
Original line number Diff line number Diff line
@@ -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;

}

tools/testing/selftests/rseq/rseq.h

+1 −0
Original line number Diff line number Diff line
@@ -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)

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