On 11.10.2018 16:25, Brad Smith wrote: > On 10/11/2018 5:41 AM, Kamil Rytarowski wrote: > >> On 11.10.2018 11:36, Peter Maydell wrote: >>> On 11 October 2018 at 00:55, Brad Smith <b...@comstyle.com> wrote: >>>> And from FreeBSD... >>>> >>>> MAP_STACK MAP_STACK implies MAP_ANON, and offset of 0. The fd >>>> argument must be -1 and prot must include at least >>>> PROT_READ and PROT_WRITE. >>>> >>>> This option creates a memory region that grows to at >>>> most len bytes in size, starting from the stack top >>>> and growing down. The stack top is the starting >>>> address returned by the call, plus len bytes. The >>>> bottom of the stack at maximum growth is the starting >>>> address returned by the call. >>>> >>>> Stacks created with MAP_STACK automatically grow. >>>> Guards prevent inadvertent use of the regions into >>>> which those stacks can grow without requiring mapping >>>> the whole stack in advance. >>> Hmm. That "automatically growing" part sounds like >>> behaviour we definitely do not want for our use case. >>> So we're going to need to make this OS-specific :-( >>> >> I propose to restrict MAP_STACK it to OpenBSD (with a comment in the >> code). Once it will be needed by someone else will be able to enable it >> for other OSes. > > I was going to propose doing something like that but you had replied > before I did. > What sort of comment did you have in mind? >
Why do we want it only on OpenBSD and its either unneeded or meaning something else on other OSes. #ifdef __OpenBSD__ flags |= MAP_STACK; #endif
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