In order to integrate rseq into user-space applications, expose a
reference counter TLS as a __rseq_refcount weak symbol so many rseq
users can be linked into the same application (e.g. librseq and glibc).
The reference count ensures that rseq syscall
registration/unregistration happens only for the most early/late user
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@xxxxxxxxxxxx>
CC: Shuah Khan <shuah@xxxxxxxxxx>
CC: Carlos O'Donell <carlos@xxxxxxxxxx>
CC: Florian Weimer <fweimer@xxxxxxxxxx>
CC: Joseph Myers <joseph@xxxxxxxxxxxxxxxx>
CC: Szabolcs Nagy <szabolcs.nagy@xxxxxxx>
CC: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CC: Ben Maurer <bmaurer@xxxxxx>
CC: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CC: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
CC: Boqun Feng <boqun.feng@xxxxxxxxx>
CC: Will Deacon <will.deacon@xxxxxxx>
CC: Dave Watson <davejwatson@xxxxxx>
CC: Paul Turner <pjt@xxxxxxxxxx>
CC: linux-api@xxxxxxxxxxxxxxx
---
Changes since v1:
- Error out on refcount overflow/underflow.
- Expose __rseq_refcount weak symbol.
---
tools/testing/selftests/rseq/rseq.c | 23 ++++++++++++++++-------
tools/testing/selftests/rseq/rseq.h | 1 +
2 files changed, 17 insertions(+), 7 deletions(-)
diff --git a/tools/testing/selftests/rseq/rseq.c b/tools/testing/selftests/rseq/rseq.c
index 4847e97ed049..835e3917d220 100644
--- a/tools/testing/selftests/rseq/rseq.c
+++ b/tools/testing/selftests/rseq/rseq.c
@@ -25,18 +25,19 @@
#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
+__attribute__((weak)) __thread
volatile struct rseq __rseq_abi = {
.cpu_id = RSEQ_CPU_ID_UNINITIALIZED,
};
-static __attribute__((tls_model("initial-exec"))) __thread
-volatile int refcount;
+__attribute__((weak)) __thread
+volatile uint32_t __rseq_refcount;
static void signal_off_save(sigset_t *oldset)
{
@@ -70,7 +71,11 @@ int rseq_register_current_thread(void)
sigset_t oldset;
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 +83,9 @@ 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;
@@ -92,7 +97,11 @@ int rseq_unregister_current_thread(void)
sigset_t oldset;
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);
diff --git a/tools/testing/selftests/rseq/rseq.h b/tools/testing/selftests/rseq/rseq.h
index c72eb70f9b52..47f815c19cef 100644
--- a/tools/testing/selftests/rseq/rseq.h
+++ b/tools/testing/selftests/rseq/rseq.h
@@ -45,6 +45,7 @@
#endif
extern __thread volatile struct rseq __rseq_abi;
+extern __thread volatile uint32_t __rseq_refcount;
#define rseq_likely(x) __builtin_expect(!!(x), 1)
#define rseq_unlikely(x) __builtin_expect(!!(x), 0)
--
2.11.0
