[PATCH] rseq/selftests: ensure the rseq abi TLS is actually 1024 bytes

[Michael Jeanson]

Adding the aligned(1024) attribute to the definition of __rseq_abi did
not increase its size to 1024, for this attribute to impact the size of
__rseq_abi it would need to be added to the declaration of 'struct
rseq_abi'. We only want to increase the size of the TLS allocation to
ensure registration will succeed with future extended ABI. Use a union
with a dummy member to ensure we allocate 1024 bytes.

Signed-off-by: Michael Jeanson <mjean...@efficios.com>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoy...@efficios.com>
---
 tools/testing/selftests/rseq/rseq.c | 21 ++++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/tools/testing/selftests/rseq/rseq.c 
b/tools/testing/selftests/rseq/rseq.c
index f6156790c3b4..aa9ae866bc1a 100644
--- a/tools/testing/selftests/rseq/rseq.c
+++ b/tools/testing/selftests/rseq/rseq.c
@@ -71,9 +71,20 @@ static int rseq_ownership;
 /* Original struct rseq allocation size is 32 bytes. */
 #define ORIG_RSEQ_ALLOC_SIZE           32
 
+/*
+ * Use a union to ensure we allocate a TLS area of 1024 bytes to accomodate an
+ * rseq registration that is larger than the current rseq ABI.
+ */
+union rseq {
+       struct rseq_abi abi;
+       char dummy[RSEQ_THREAD_AREA_ALLOC_SIZE];
+};
+
 static
-__thread struct rseq_abi __rseq_abi __attribute__((tls_model("initial-exec"), 
aligned(RSEQ_THREAD_AREA_ALLOC_SIZE))) = {
-       .cpu_id = RSEQ_ABI_CPU_ID_UNINITIALIZED,
+__thread union rseq __rseq __attribute__((tls_model("initial-exec"))) = {
+       .abi = {
+               .cpu_id = RSEQ_ABI_CPU_ID_UNINITIALIZED,
+       },
 };
 
 static int sys_rseq(struct rseq_abi *rseq_abi, uint32_t rseq_len,
@@ -149,7 +160,7 @@ int rseq_register_current_thread(void)
                /* Treat libc's ownership as a successful registration. */
                return 0;
        }
-       rc = sys_rseq(&__rseq_abi, get_rseq_min_alloc_size(), 0, RSEQ_SIG);
+       rc = sys_rseq(&__rseq.abi, get_rseq_min_alloc_size(), 0, RSEQ_SIG);
        if (rc) {
                /*
                 * After at least one thread has registered successfully
@@ -183,7 +194,7 @@ int rseq_unregister_current_thread(void)
                /* Treat libc's ownership as a successful unregistration. */
                return 0;
        }
-       rc = sys_rseq(&__rseq_abi, get_rseq_min_alloc_size(), 
RSEQ_ABI_FLAG_UNREGISTER, RSEQ_SIG);
+       rc = sys_rseq(&__rseq.abi, get_rseq_min_alloc_size(), 
RSEQ_ABI_FLAG_UNREGISTER, RSEQ_SIG);
        if (rc)
                return -1;
        return 0;
@@ -249,7 +260,7 @@ void rseq_init(void)
        rseq_ownership = 1;
 
        /* Calculate the offset of the rseq area from the thread pointer. */
-       rseq_offset = (void *)&__rseq_abi - rseq_thread_pointer();
+       rseq_offset = (void *)&__rseq.abi - rseq_thread_pointer();
 
        /* rseq flags are deprecated, always set to 0. */
        rseq_flags = 0;
-- 
2.43.0