Date: Thu, 24 Jul 2003 20:17:02 +0200 From: Steve O'Hara-Smith <steve@sohara.org> To: Barney Wolff <barney@databus.com> Cc: freebsd-stable@freebsd.org Subject: Re: malloc does not return null when out of memory Message-ID: <20030724201702.6667b707.steve@sohara.org> In-Reply-To: <20030724164522.GA39964@pit.databus.com> References: <20030723173427.GA72876@vmunix.com> <20030723173427.GA72876@vmunix.com> <5.2.0.9.0.20030723234250.052821e8@192.168.0.12> <20030724070936.GA16762@rot13.obsecurity.org> <3F1FF81F.5050701@mac.com> <20030724164522.GA39964@pit.databus.com>
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On Thu, 24 Jul 2003 12:45:22 -0400
Barney Wolff <barney@databus.com> wrote:
BW> On Thu, Jul 24, 2003 at 11:15:43AM -0400, Chuck Swiger wrote:
BW> >
BW> > +/* write a single byte per page to disable overcommit behavior */
BW> > +static int malloc_overcommit;
BW>
BW> Won't this merely die in malloc, not return 0?
Yes - it needs to trap the SEGV as well to produce the wanted
behaviour, something like:
+ else if (malloc_overcommit) {
+ ocsighandleron();
+ for (stride = 0; stride <= size; stride += malloc_pagesize) {
+ ((char *)result)[stride] = SOME_JUNK;
+ if (ocsignalled) {
+ ocsighandleroff();
+ return NULL;
+ }
+ }
+ ocsighandleroff();
+ }
Where ocsighandleron() installs a SEGV handler that sets ocsignalled
when called and ocsighandleroff() installs the original one.
BTW malloc_overcommit seems to be upside down, I left it that way.
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