linux-user/syscall.c: Don't warn about unimplemented get_robust_list
The nature of the kernel ABI for the get_robust_list and set_robust_list
syscalls means we cannot implement them in QEMU. Make get_robust_list
silently return ENOSYS rather than using the default "print message and
then fail ENOSYS" code path, in the same way we already do for
set_robust_list, and add a comment documenting why we do this.
This silences warnings which were being produced for emulating
even trivial programs like 'ls' in x86-64-on-x86-64.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Riku Voipio <riku.voipio@linaro.org>
diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 6182a27..ee82a2d 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -8631,7 +8631,20 @@
#ifdef TARGET_NR_set_robust_list
case TARGET_NR_set_robust_list:
- goto unimplemented_nowarn;
+ case TARGET_NR_get_robust_list:
+ /* The ABI for supporting robust futexes has userspace pass
+ * the kernel a pointer to a linked list which is updated by
+ * userspace after the syscall; the list is walked by the kernel
+ * when the thread exits. Since the linked list in QEMU guest
+ * memory isn't a valid linked list for the host and we have
+ * no way to reliably intercept the thread-death event, we can't
+ * support these. Silently return ENOSYS so that guest userspace
+ * falls back to a non-robust futex implementation (which should
+ * be OK except in the corner case of the guest crashing while
+ * holding a mutex that is shared with another process via
+ * shared memory).
+ */
+ goto unimplemented_nowarn;
#endif
#if defined(TARGET_NR_utimensat) && defined(__NR_utimensat)
