tcg: Workaround macOS 11.2 mprotect bug

There's a change in mprotect() behaviour [1] in the latest macOS
on M1 and it's not yet clear if it's going to be fixed by Apple.

As a short-term fix, ignore failures setting up the guard pages.

[1] https://gist.github.com/hikalium/75ae822466ee4da13cbbe486498a191f

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Tested-by: Roman Bolshakov <r.bolshakov@yadro.com>
Reviewed-by: Roman Bolshakov <r.bolshakov@yadro.com>
Buglink: https://bugs.launchpad.net/qemu/+bug/1914849
Message-Id: <20210320165720.1813545-3-richard.henderson@linaro.org>

1 files changed, 7 insertions, 3 deletions

diff --git a/tcg/tcg.c b/tcg/tcg.c
index 88c9e6f..1fbe0b6 100644
--- a/tcg/tcg.c
+++ b/tcg/tcg.c
@@ -864,11 +864,15 @@ void tcg_region_init(void)
      */
     for (i = 0; i < region.n; i++) {
         void *start, *end;
-        int rc;
 
         tcg_region_bounds(i, &start, &end);
-        rc = qemu_mprotect_none(end, page_size);
-        g_assert(!rc);
+
+        /*
+         * macOS 11.2 has a bug (Apple Feedback FB8994773) in which mprotect
+         * rejects a permission change from RWX -> NONE.  Guard pages are
+         * nice for bug detection but are not essential; ignore any failure.
+         */
+        (void)qemu_mprotect_none(end, page_size);
     }
 
     tcg_region_trees_init();