From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:45220) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bMyny-0007s6-Nl for qemu-devel@nongnu.org; Tue, 12 Jul 2016 10:36:59 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bMynt-0002pk-Jc for qemu-devel@nongnu.org; Tue, 12 Jul 2016 10:36:57 -0400 Received: from mx-v6.kamp.de ([2a02:248:0:51::16]:46494 helo=mx01.kamp.de) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bMynt-0002pc-AR for qemu-devel@nongnu.org; Tue, 12 Jul 2016 10:36:53 -0400 Message-ID: <57850082.1040502@kamp.de> Date: Tue, 12 Jul 2016 16:36:50 +0200 From: Peter Lieven MIME-Version: 1.0 References: <1468228082-7492-1-git-send-email-pl@kamp.de> <1468228082-7492-2-git-send-email-pl@kamp.de> <5783CBD4.2000205@redhat.com> In-Reply-To: <5783CBD4.2000205@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH V4 1/6] oslib-posix: add helpers for stack alloc and free List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Eric Blake , qemu-devel@nongnu.org Cc: kwolf@redhat.com, mreitz@redhat.com, pbonzini@redhat.com, mst@redhat.com, dgilbert@redhat.com, peter.maydell@linaro.org, rth@twiddle.net, armbru@redhat.com Am 11.07.2016 um 18:39 schrieb Eric Blake: > On 07/11/2016 03:07 AM, Peter Lieven wrote: >> the allocated stack will be adjusted to the minimum supported stack size >> by the OS and rounded up to be a multiple of the system pagesize. >> Additionally an architecture dependent guard page is added to the stack >> to catch stack overflows. >> >> Signed-off-by: Peter Lieven >> --- >> include/sysemu/os-posix.h | 23 +++++++++++++++++++++++ >> util/oslib-posix.c | 44 ++++++++++++++++++++++++++++++++++++++++++++ >> 2 files changed, 67 insertions(+) >> >> + >> +static size_t adjust_stack_size(size_t sz) >> +{ >> + /* avoid stacks smaller than _SC_THREAD_STACK_MIN */ >> + sz = MAX(sz, sysconf(_SC_THREAD_STACK_MIN)); > sz is unsigned, but sysconf() is signed. Furthermore, sysconf() is > permitted to return -1 if there is no such minimum. MAX() would then > operate on the common integral promotion between the two arguments, > which may treat (unsigned)(-1) as the larger of the two values, and give > you the wrong results. > > I think it is theoretical (all platforms that we compile on have a > working sysconf(_SC_THREAD_STACK_MIN), right?), but still may be worth > being sure that sysconf() returned a positive value before computing MAX(). > If you feel more comfortable I can surround it by a if (sysconf(_SC_THREAD_STACK_MIN) > 0) { } I wonder if the _SC_THREAD_STACK_MIN constant exists if there is no minimum? Peter