Re: [PATCH v3 for-6.0 2/2] tcg: Workaround macOS 11.2 mprotect bug

[Philippe Mathieu-Daudé]

On 3/20/21 5:57 PM, Richard Henderson wrote:
> 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
> 
> Buglink: https://bugs.launchpad.net/qemu/+bug/1914849
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  tcg/tcg.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/tcg/tcg.c b/tcg/tcg.c
> index 88c9e6f8a4..1fbe0b686d 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);

What about:

#ifdef CONFIG_DARWIN

           /* ... */
           (void)rc;
#else

> -        g_assert(!rc);

#endif

> +
> +        /*
> +         * 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();
>