On 6/30/23 20:46, Warner Losh wrote:
>
>
> On Fri, Jun 30, 2023 at 7:22 AM Richard Henderson <richard.henderson@linaro.org
> <mailto:richard.henderson@linaro.org>> wrote:
>
> The previous check returned -1 when any page within
> [start, start+len) is unmapped, not when all are unmapped.
>
> Cc: Warner Losh <imp@bsdimp.com <mailto:imp@bsdimp.com>>
> Cc: Kyle Evans <kevans@freebsd.org <mailto:kevans@freebsd.org>>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org
> <mailto:richard.henderson@linaro.org>>
> ---
> bsd-user/mmap.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/bsd-user/mmap.c b/bsd-user/mmap.c
> index 565b9f97ed..07b5b8055e 100644
> --- a/bsd-user/mmap.c
> +++ b/bsd-user/mmap.c
> @@ -609,7 +609,7 @@ abi_long target_mmap(abi_ulong start, abi_ulong len, int prot,
> }
>
> /* Reject the mapping if any page within the range is mapped */
> - if ((flags & MAP_EXCL) && page_check_range(start, len, 0) < 0) {
> + if ((flags & MAP_EXCL) && !page_check_range_empty(start, end - 1)) {
>
>
> Won't computing end overflow if start is 1<<32 - len? Then subtracting one here would be
> too late.
-fwrapv, so fully twos-compliment.
So start per above, end == 0, end - 1 == UINT32_MAX.
See also the rest of the linux-user code, wherein I work with "last == end - 1".
Which has the advantage of preserving comparison order: start < last.
r~