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Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.11.0 Subject: Re: [PATCH 08/24] bsd-user: Use page_check_range_empty for MAP_EXCL Content-Language: en-US To: Warner Losh Cc: qemu-devel@nongnu.org, mjt@tls.msk.ru, laurent@vivier.eu, Kyle Evans References: <20230630132159.376995-1-richard.henderson@linaro.org> <20230630132159.376995-9-richard.henderson@linaro.org> From: Richard Henderson In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=2a00:1450:4864:20::332; envelope-from=richard.henderson@linaro.org; helo=mail-wm1-x332.google.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.095, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 6/30/23 20:46, Warner Losh wrote: > > > On Fri, Jun 30, 2023 at 7:22 AM Richard Henderson > wrote: > > The previous check returned -1 when any page within > [start, start+len) is unmapped, not when all are unmapped. > > Cc: Warner Losh > > Cc: Kyle Evans > > Signed-off-by: Richard Henderson > > --- >  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~