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zdtm: Fix rseq01 test for kernel 7.0 rseq changes

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Starting with Linux 7.0, the rseq feature size has grown to 33 bytes
and AT_RSEQ_ALIGN has increased to 64.  This causes sizeof(struct rseq)
from the uapi header to be 64 (33 bytes padded to aligned(32)), while
the actual registration size used by glibc (__rseq_size) is 33.

The rseq01 test was using sizeof(struct rseq) as the registration
size and a test-local __rseq_abi variable (with only 32-byte
alignment from the uapi header) as the rseq area.  Both are
wrong on kernel 7.0:

 - The kernel now checks alignment against __alignof__(struct rseq)
   which is 64 internally; the 32-byte-aligned test variable may
   not satisfy this.

 - sizeof(struct rseq) = 64 does not match the feature size of 33
   that glibc registered with, so re-registration with a different
   size fails.

Fix by:

 - Using __rseq_size (the feature size reported by glibc) as the
   registration size instead of sizeof(struct rseq).

 - Using the glibc-provided rseq area (at thread_pointer() +
   __rseq_offset) which is allocated with proper AT_RSEQ_ALIGN
   alignment, instead of a test-local variable.

Both fall back to the previous behavior when glibc rseq support
is not available.

This mirrors the glibc fix:

    https://sourceware.org/cgit/glibc/commit/?id=67f303b47dc584f204e3f2441b9832082415eebc

Assisted-by: Claude Code (claude-opus-4-6):claude-opus-4-6@default
Signed-off-by: Adrian Reber <areber@redhat.com>
This commit is contained in:
Adrian Reber 2026-04-21 09:30:17 +00:00 • committed by Alexander Mikhalitsyn
parent 002d5e9ae3
commit 48bb31e46a
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GPG key ID: B1F47F5CB05B4FA3
1 changed files with 50 additions and 9 deletions
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59
test/zdtm/transition/rseq01.c
View file

@ -20,9 +20,19 @@
#endif
#endif
/*
* HAVE_GLIBC_RSEQ is set when the C library provides rseq support
* (__rseq_size, __rseq_offset). glibc >= 2.35 defines RSEQ_SIG in
* <sys/rseq.h>; musl does not, so the test falls back to its own
* definitions below.
*/
#if defined(RSEQ_SIG)
#define HAVE_GLIBC_RSEQ 1
#endif
#if defined(__x86_64__)
#if defined(__x86_64__) && defined(RSEQ_SIG)
#ifdef HAVE_GLIBC_RSEQ
static inline void *thread_pointer(void)
{
void *result;
@ -38,11 +48,11 @@ static inline void unregister_old_rseq(void)
size = 32;
syscall(__NR_rseq, (void *)((char *)thread_pointer() + __rseq_offset), size, 1, RSEQ_SIG);
}
#else
#else /* !HAVE_GLIBC_RSEQ */
static inline void unregister_old_rseq(void)
{
}
#endif
#endif /* HAVE_GLIBC_RSEQ */
const char *test_doc = "rseq() transition test";
const char *test_author = "Alexander Mikhalitsyn <alexander.mikhalitsyn@virtuozzo.com>";
@ -97,11 +107,27 @@ static int sys_rseq(volatile struct rseq *rseq_abi, uint32_t rseq_len, int flags
return syscall(__NR_rseq, rseq_abi, rseq_len, flags, sig);
}
/*
* Return the rseq registration size. Starting with Linux 7.0,
* AT_RSEQ_ALIGN is 64 but the feature size is 33, so sizeof(struct rseq)
* (padded to alignment) no longer matches the registration size the kernel
* expects. Use __rseq_size when available, clamped to a minimum of 32
* for older kernels (mirroring glibc's rseq-internal.h).
*/
static uint32_t rseq_reg_size(void)
{
#ifdef HAVE_GLIBC_RSEQ
if (__rseq_size)
return (__rseq_size < 32) ? 32 : __rseq_size;
#endif
return sizeof(struct rseq);
}
static void register_thread(void)
{
int rc;
unregister_old_rseq();
rc = sys_rseq(rseq_ptr, sizeof(struct rseq), 0, RSEQ_SIG);
rc = sys_rseq(rseq_ptr, rseq_reg_size(), 0, RSEQ_SIG);
if (rc) {
fail("Failed to register rseq");
exit(1);
@ -111,7 +137,7 @@ static void register_thread(void)
static void check_thread(void)
{
int rc;
rc = sys_rseq(rseq_ptr, sizeof(struct rseq), 0, RSEQ_SIG);
rc = sys_rseq(rseq_ptr, rseq_reg_size(), 0, RSEQ_SIG);
if (!(rc && errno == EBUSY)) {
fail("Failed to check rseq %d", rc);
exit(1);
@ -206,12 +232,27 @@ static intptr_t *cpu_data;
bool ignore_abort = true;
int thread_ret;
static volatile struct rseq *rseq_area(void)
{
#ifdef HAVE_GLIBC_RSEQ
/*
* Use the glibc-provided rseq area which is allocated with the
* correct alignment (AT_RSEQ_ALIGN, 64 on kernel >= 7.0).
* The test-local __rseq_abi only has the uapi header alignment
* (32 bytes) which may not satisfy the kernel's requirement.
*/
if (__rseq_size)
return (volatile struct rseq *)((char *)thread_pointer() + __rseq_offset);
#endif
return &__rseq_abi;
}
void *thread_routine(void *args)
{
int cpu;
rseq_ptr = &__rseq_abi;
memset((void *)rseq_ptr, 0, sizeof(struct rseq));
rseq_ptr = rseq_area();
memset((void *)rseq_ptr, 0, rseq_reg_size());
register_thread();
task_waiter_complete(&waiter, 1);
task_waiter_wait4(&waiter, 2);
@ -235,8 +276,8 @@ int main(int argc, char *argv[])
long nr_cpus;
pthread_t thread;
rseq_ptr = &__rseq_abi;
memset((void *)rseq_ptr, 0, sizeof(struct rseq));
rseq_ptr = rseq_area();
memset((void *)rseq_ptr, 0, rseq_reg_size());
test_init(argc, argv);
nr_cpus = sysconf(_SC_NPROCESSORS_ONLN);