On 31 December 2015 at 08:12, <cheng...@emindsoft.com.cn> wrote:
> From: Chen Gang <cheng...@emindsoft.com.cn>
>
> mmap() size in mmap_frag() is qemu_host_page_size, but the outside calls
> page_set_flags() may be not with qemu_host_page_size. So after mmap(),
> call page_set_flags() in time.
>
> Also let addr increasing step be TARGET_PAGE_SIZE, just like another
> areas have done.
>
> Also remove useless variable p.
Please don't do multiple things in a single patch. This patch
has all of:
* a fix for an unnecessary inefficiency
* a coding style change with no functional effects
* a bug fix
Mixing them up together like this makes it harder to evaluate
the bug fix, which is the important part of the change.
> Signed-off-by: Chen Gang <gang.chen.5...@gmail.com>
> ---
> linux-user/mmap.c | 10 ++++++----
> 1 files changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/linux-user/mmap.c b/linux-user/mmap.c
> index 445e8c6..7920c5e 100644
> --- a/linux-user/mmap.c
> +++ b/linux-user/mmap.c
> @@ -151,17 +151,19 @@ static int mmap_frag(abi_ulong real_start,
>
> /* get the protection of the target pages outside the mapping */
> prot1 = 0;
> - for(addr = real_start; addr < real_end; addr++) {
> + for (addr = real_start; addr < real_end; addr += TARGET_PAGE_SIZE) {
> if (addr < start || addr >= end)
> prot1 |= page_get_flags(addr);
> }
>
> if (prot1 == 0) {
> /* no page was there, so we allocate one */
> - void *p = mmap(host_start, qemu_host_page_size, prot,
> - flags | MAP_ANONYMOUS, -1, 0);
> - if (p == MAP_FAILED)
> + if (mmap(host_start, qemu_host_page_size, prot, flags |
> MAP_ANONYMOUS,
> + -1, 0) == MAP_FAILED) {
> return -1;
> + }
> + page_set_flags(real_start, real_start + qemu_host_page_size,
> + prot | PAGE_VALID);
I'm not convinced this is right -- it will mean that we set
the page flags for every target page in this host page to
be the same thing (the ORed together result we calculated).
I don't think we want to update the page flags like that --
if one target page was read-only and the other read-write then
we need to make the whole host page read-write (since it's
bigger and covers both target pages), but we don't want to
incorrectly record that the first target-page is read-write.
I don't really understand this mmap code, though -- that's just
the result of looking at it for fifteen minutes or so.
> prot1 = prot;
> }
> prot1 &= PAGE_BITS;
> --
> 1.7.3.4
>
thanks
-- PMM
