glibc-2.35 (upcoming release date 2022-02-01) exposes the rseq per-thread data in the TCB, accessible at an offset from the thread pointer, rather than through an actual Thread-Local Storage (TLS) variable, as the Linux kernel selftests initially expected.
The __rseq_abi TLS and glibc-2.35's ABI for per-thread data cannot actively coexist in a process, because the kernel supports only a single rseq registration per thread.
Here is the scheme introduced to ensure selftests can work both with an older glibc and with glibc-2.35+:
- librseq exposes its own "rseq_offset, rseq_size, rseq_flags" ABI.
- librseq queries for glibc rseq ABI (__rseq_offset, __rseq_size, __rseq_flags) using dlsym() in a librseq library constructor. If those are found, copy their values into rseq_offset, rseq_size, and rseq_flags.
- Else, if those glibc symbols are not found, handle rseq registration from librseq and use its own IE-model TLS to implement the rseq ABI per-thread storage.
Signed-off-by: Mathieu Desnoyers mathieu.desnoyers@efficios.com --- tools/testing/selftests/rseq/Makefile | 2 +- tools/testing/selftests/rseq/rseq.c | 161 ++++++++++++-------------- tools/testing/selftests/rseq/rseq.h | 13 ++- 3 files changed, 88 insertions(+), 88 deletions(-)
diff --git a/tools/testing/selftests/rseq/Makefile b/tools/testing/selftests/rseq/Makefile index 2af9d39a9716..215e1067f037 100644 --- a/tools/testing/selftests/rseq/Makefile +++ b/tools/testing/selftests/rseq/Makefile @@ -6,7 +6,7 @@ endif
CFLAGS += -O2 -Wall -g -I./ -I../../../../usr/include/ -L$(OUTPUT) -Wl,-rpath=./ \ $(CLANG_FLAGS) -LDLIBS += -lpthread +LDLIBS += -lpthread -ldl
# Own dependencies because we only want to build against 1st prerequisite, but # still track changes to header files and depend on shared object. diff --git a/tools/testing/selftests/rseq/rseq.c b/tools/testing/selftests/rseq/rseq.c index 1f905b60728a..07ba0d463a96 100644 --- a/tools/testing/selftests/rseq/rseq.c +++ b/tools/testing/selftests/rseq/rseq.c @@ -26,130 +26,123 @@ #include <assert.h> #include <signal.h> #include <limits.h> +#include <dlfcn.h>
#include "../kselftest.h" #include "rseq.h"
-__thread struct rseq_abi __rseq_abi = { - .cpu_id = RSEQ_ABI_CPU_ID_UNINITIALIZED, -}; +static const int *libc_rseq_offset_p; +static const unsigned int *libc_rseq_size_p; +static const unsigned int *libc_rseq_flags_p;
-/* - * 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; +/* Offset from the thread pointer to the rseq area. */ +int rseq_offset; + +/* Size of the registered rseq area. 0 if the registration was + unsuccessful. */ +unsigned int rseq_size = -1U; + +/* Flags used during rseq registration. */ +unsigned int rseq_flags;
-/* Whether this library have ownership of rseq registration. */ static int rseq_ownership;
-static __thread volatile uint32_t __rseq_refcount; +static +__thread struct rseq_abi __rseq_abi __attribute__((tls_model("initial-exec"))) = { + .cpu_id = RSEQ_ABI_CPU_ID_UNINITIALIZED, +};
-static void signal_off_save(sigset_t *oldset) +static int sys_rseq(struct rseq_abi *rseq_abi, uint32_t rseq_len, + int flags, uint32_t sig) { - sigset_t set; - int ret; - - sigfillset(&set); - ret = pthread_sigmask(SIG_BLOCK, &set, oldset); - if (ret) - abort(); + return syscall(__NR_rseq, rseq_abi, rseq_len, flags, sig); }
-static void signal_restore(sigset_t oldset) +int rseq_available(void) { - int ret; + int rc;
- ret = pthread_sigmask(SIG_SETMASK, &oldset, NULL); - if (ret) + rc = sys_rseq(NULL, 0, 0, 0); + if (rc != -1) abort(); -} - -static int sys_rseq(volatile struct rseq_abi *rseq_abi, uint32_t rseq_len, - int flags, uint32_t sig) -{ - return syscall(__NR_rseq, rseq_abi, rseq_len, flags, sig); + switch (errno) { + case ENOSYS: + return 0; + case EINVAL: + return 1; + default: + abort(); + } }
int rseq_register_current_thread(void) { - int rc, ret = 0; - sigset_t oldset; + int rc;
- if (!rseq_ownership) + if (!rseq_ownership) { + /* Treat libc's ownership as a successful registration. */ return 0; - signal_off_save(&oldset); - if (__rseq_refcount == UINT_MAX) { - ret = -1; - goto end; } - if (__rseq_refcount++) - goto end; rc = sys_rseq(&__rseq_abi, sizeof(struct rseq_abi), 0, RSEQ_SIG); - if (!rc) { - assert(rseq_current_cpu_raw() >= 0); - goto end; - } - if (errno != EBUSY) - RSEQ_WRITE_ONCE(__rseq_abi.cpu_id, RSEQ_ABI_CPU_ID_REGISTRATION_FAILED); - ret = -1; - __rseq_refcount--; -end: - signal_restore(oldset); - return ret; + if (rc) + return -1; + assert(rseq_current_cpu_raw() >= 0); + return 0; }
int rseq_unregister_current_thread(void) { - int rc, ret = 0; - sigset_t oldset; + int rc;
- if (!rseq_ownership) + if (!rseq_ownership) { + /* Treat libc's ownership as a successful unregistration. */ return 0; - signal_off_save(&oldset); - if (!__rseq_refcount) { - ret = -1; - goto end; } - if (--__rseq_refcount) - goto end; - rc = sys_rseq(&__rseq_abi, sizeof(struct rseq_abi), - RSEQ_ABI_FLAG_UNREGISTER, RSEQ_SIG); - if (!rc) - goto end; - __rseq_refcount = 1; - ret = -1; -end: - signal_restore(oldset); - return ret; + rc = sys_rseq(&__rseq_abi, sizeof(struct rseq_abi), RSEQ_ABI_FLAG_UNREGISTER, RSEQ_SIG); + if (rc) + return -1; + return 0; }
-int32_t rseq_fallback_current_cpu(void) +static __attribute__((constructor)) +void rseq_init(void) { - int32_t cpu; - - cpu = sched_getcpu(); - if (cpu < 0) { - perror("sched_getcpu()"); - abort(); + libc_rseq_offset_p = dlsym(RTLD_NEXT, "__rseq_offset"); + libc_rseq_size_p = dlsym(RTLD_NEXT, "__rseq_size"); + libc_rseq_flags_p = dlsym(RTLD_NEXT, "__rseq_flags"); + if (libc_rseq_size_p && libc_rseq_offset_p && libc_rseq_flags_p) { + /* rseq registration owned by glibc */ + rseq_offset = *libc_rseq_offset_p; + rseq_size = *libc_rseq_size_p; + rseq_flags = *libc_rseq_flags_p; + return; } - return cpu; -} - -void __attribute__((constructor)) rseq_init(void) -{ - /* Check whether rseq is handled by another library. */ - if (__rseq_handled) + if (!rseq_available()) return; - __rseq_handled = 1; rseq_ownership = 1; + rseq_offset = (void *)&__rseq_abi - rseq_thread_pointer(); + rseq_size = sizeof(struct rseq_abi); + rseq_flags = 0; }
-void __attribute__((destructor)) rseq_fini(void) +static __attribute__((destructor)) +void rseq_exit(void) { if (!rseq_ownership) return; - __rseq_handled = 0; + rseq_offset = 0; + rseq_size = -1U; rseq_ownership = 0; } + +int32_t rseq_fallback_current_cpu(void) +{ + int32_t cpu; + + cpu = sched_getcpu(); + if (cpu < 0) { + perror("sched_getcpu()"); + abort(); + } + return cpu; +} diff --git a/tools/testing/selftests/rseq/rseq.h b/tools/testing/selftests/rseq/rseq.h index ca668a2af172..17531ccd3090 100644 --- a/tools/testing/selftests/rseq/rseq.h +++ b/tools/testing/selftests/rseq/rseq.h @@ -43,12 +43,19 @@ #define RSEQ_INJECT_FAILED #endif
-extern __thread struct rseq_abi __rseq_abi; -extern int __rseq_handled; +#include "rseq-thread-pointer.h" + +/* Offset from the thread pointer to the rseq area. */ +extern int rseq_offset; +/* Size of the registered rseq area. 0 if the registration was + unsuccessful. */ +extern unsigned int rseq_size; +/* Flags used during rseq registration. */ +extern unsigned int rseq_flags;
static inline struct rseq_abi *rseq_get_abi(void) { - return &__rseq_abi; + return (struct rseq_abi *) ((uintptr_t) rseq_thread_pointer() + rseq_offset); }
#define rseq_likely(x) __builtin_expect(!!(x), 1)