Re: [Qemu-devel] [PATCH v2] linux-user/mmap.c: Always zero MAP_ANONYMOUS memory in mmap_frag()

[Laurent Vivier]

Le 21/12/2015 03:33, address@hidden a écrit :
> From: Chen Gang <address@hidden>
> 
> When mapping MAP_ANONYMOUS memory fragments, still need notice about to
> set it zero, or it will cause issues.

Perhaps you can explain in the commit message why this page is not
already filled by zeros ?

> Signed-off-by: Chen Gang <address@hidden>
> ---
>  linux-user/mmap.c |    4 +++-
>  1 files changed, 3 insertions(+), 1 deletions(-)
> 
> diff --git a/linux-user/mmap.c b/linux-user/mmap.c
> index 7b459d5..29fe646 100644
> --- a/linux-user/mmap.c
> +++ b/linux-user/mmap.c
> @@ -186,10 +186,12 @@ static int mmap_frag(abi_ulong real_start,
>          if (prot_new != (prot1 | PROT_WRITE))
>              mprotect(host_start, qemu_host_page_size, prot_new);
>      } else {
> -        /* just update the protection */
>          if (prot_new != prot1) {
>              mprotect(host_start, qemu_host_page_size, prot_new);
>          }
> +        if ((prot_new & PROT_WRITE) && ((flags & MAP_PRIVATE) || (fd == 
> -1))) {

According to manpage, for MAP_ANONYMOUS, fd can be ignored.
Why do you check if the page is MAP_PRIVATE or not ?

> +            memset(g2h(start), 0, end - start);
> +        }
>      }
>      return 0;
>  }
>