Date: Mon, 10 Jun 2019 01:42:34 -0500 From: Doug Moore <dougm@rice.edu> To: Andriy Gapon <avg@FreeBSD.org>, Doug Moore <dougm@freebsd.org>, src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r348843 - head/sys/vm Message-ID: <21baf615-3356-73a1-52b0-d2f33f4cf49d@rice.edu> In-Reply-To: <c54a0e35-d5c6-0711-d2bb-01e3dca802c3@FreeBSD.org> References: <201906100307.x5A37BFt099669@repo.freebsd.org> <c54a0e35-d5c6-0711-d2bb-01e3dca802c3@FreeBSD.org>
next in thread | previous in thread | raw e-mail | index | archive | help
-fwrapv concerns signed arithmetic. This calculation is with unsigned arithmetic, and the possibility of wrapping around to 0 is part of the language. Doug Moore On 6/10/19 1:35 AM, Andriy Gapon wrote: > On 10/06/2019 06:07, Doug Moore wrote: >> Author: dougm >> Date: Mon Jun 10 03:07:10 2019 >> New Revision: 348843 >> URL: https://svnweb.freebsd.org/changeset/base/348843 >> >> Log: >> There are times when a len==0 parameter to mmap is okay. But on a >> 32-bit machine, a len parameter just a few bytes short of 4G, rounded >> up to a page boundary and hitting zero then, is not okay. Return >> failure in that case. >> >> Reported by: pho >> Reviewed by: alc, kib (mentor) >> Tested by: pho >> Differential Revision: https://reviews.freebsd.org/D20580 >> >> Modified: >> head/sys/vm/vm_mmap.c >> >> Modified: head/sys/vm/vm_mmap.c >> ============================================================================== >> --- head/sys/vm/vm_mmap.c Sun Jun 9 22:55:21 2019 (r348842) >> +++ head/sys/vm/vm_mmap.c Mon Jun 10 03:07:10 2019 (r348843) >> @@ -257,7 +257,10 @@ kern_mmap(struct thread *td, uintptr_t addr0, size_t s >> >> /* Adjust size for rounding (on both ends). */ >> size += pageoff; /* low end... */ >> - size = (vm_size_t) round_page(size); /* hi end */ >> + /* Check for rounding up to zero. */ >> + if (round_page(size) < size) > Is this guaranteed to work with all compilers? > I think that some smart compilers may think that this condition is impossible. > Are we finally using -fwrapv or something like it for kernel builds? > >> + return (EINVAL); >> + size = round_page(size); /* hi end */ >> >> /* Ensure alignment is at least a page and fits in a pointer. */ >> align = flags & MAP_ALIGNMENT_MASK; >> >
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?21baf615-3356-73a1-52b0-d2f33f4cf49d>