Re: [PATCH 1/2] KVM: selftests: Make rseq compatible with glibc-2.35

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Hi Florian,

On 8/9/22 4:33 PM, Florian Weimer wrote:
diff --git a/tools/testing/selftests/kvm/rseq_test.c b/tools/testing/selftests/kvm/rseq_test.c
index a54d4d05a058..acb1bf1f06b3 100644
--- a/tools/testing/selftests/kvm/rseq_test.c
+++ b/tools/testing/selftests/kvm/rseq_test.c
@@ -9,6 +9,7 @@
  #include <string.h>
  #include <signal.h>
  #include <syscall.h>
+#include <dlfcn.h>
  #include <sys/ioctl.h>
  #include <sys/sysinfo.h>
  #include <asm/barrier.h>

I'm surprised that there isn't a Makefile update to link with -ldl
(still required for glibc 2.33 and earlier).


In next revision, I will add '-ldl' into tools/testing/selftests/kvm/Makefile.


@@ -36,6 +37,8 @@ static __thread volatile struct rseq __rseq = {
   */
  #define NR_TASK_MIGRATIONS 100000
+static bool __rseq_ownership;
+static volatile struct rseq *__rseq_info;
  static pthread_t migration_thread;
  static cpu_set_t possible_mask;
  static int min_cpu, max_cpu;
@@ -49,11 +52,33 @@ static void guest_code(void)
  		GUEST_SYNC(0);
  }
+static void sys_rseq_ownership(void)
+{
+	long *offset;
+	unsigned int *size, *flags;
+
+	offset = dlsym(RTLD_NEXT, "__rseq_offset");
+	size = dlsym(RTLD_NEXT, "__rseq_size");
+	flags = dlsym(RTLD_NEXT, "__rseq_flags");
+
+	if (offset && size && *size && flags) {
+		__rseq_ownership = false;
+		__rseq_info = (struct rseq *)((uintptr_t)__builtin_thread_pointer() +
+					      *offset);

__builtin_thread_pointer doesn't work on all architectures/GCC versions.
Is this a problem for selftests?


It's a problem as the test case is running on all architectures. I think I
need introduce our own __builtin_thread_pointer() for where it's not
supported: (1) PowerPC  (2) x86 without GCC 11

Please let me know if I still have missed cases where __buitin_thread_pointer()
isn't supported?

Thanks,
Gavin

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