Linux: Make __rseq_size useful for feature detection (bug 31965)

The __rseq_size value is now the active area of struct rseq
(so 20 initially), not the full struct size including padding
at the end (32 initially).

Update misc/tst-rseq to print some additional diagnostics.

Reviewed-by: Michael Jeanson <mjeanson@efficios.com>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
(cherry picked from commit 2e456ccf0c34a056e3ccafac4a0c7effef14d918)

1 files changed, 9 insertions, 1 deletions

diff --git a/sysdeps/unix/sysv/linux/tst-rseq.c b/sysdeps/unix/sysv/linux/tst-rseq.c
index 16983503b1..9f9aa7eb21 100644
--- a/sysdeps/unix/sysv/linux/tst-rseq.c
+++ b/sysdeps/unix/sysv/linux/tst-rseq.c
@@ -29,6 +29,7 @@
 # include <stdlib.h>
 # include <string.h>
 # include <syscall.h>
+# include <sys/auxv.h>
 # include <thread_pointer.h>
 # include <tls.h>
 # include "tst-rseq.h"
@@ -42,7 +43,8 @@ do_rseq_main_test (void)
   TEST_COMPARE (__rseq_flags, 0);
   TEST_VERIFY ((char *) __thread_pointer () + __rseq_offset
                == (char *) &pd->rseq_area);
-  TEST_COMPARE (__rseq_size, sizeof (pd->rseq_area));
+  /* The current implementation only supports the initial size.  */
+  TEST_COMPARE (__rseq_size, 20);
 }
 
 static void
@@ -52,6 +54,12 @@ do_rseq_test (void)
     {
       FAIL_UNSUPPORTED ("kernel does not support rseq, skipping test");
     }
+  printf ("info: __rseq_size: %u\n", __rseq_size);
+  printf ("info: __rseq_offset: %td\n", __rseq_offset);
+  printf ("info: __rseq_flags: %u\n", __rseq_flags);
+  printf ("info: getauxval (AT_RSEQ_FEATURE_SIZE): %ld\n",
+          getauxval (AT_RSEQ_FEATURE_SIZE));
+  printf ("info: getauxval (AT_RSEQ_ALIGN): %ld\n", getauxval (AT_RSEQ_ALIGN));
   do_rseq_main_test ();
 }
 #else /* RSEQ_SIG */