Date: Thu, 27 Jan 2005 14:22:01 -0500 From: David Schultz <das@FreeBSD.ORG> To: Jacques Fourie <jacques.fourie@gmail.com> Cc: freebsd-hackers@FreeBSD.ORG Subject: Re: kernel vm question Message-ID: <20050127192201.GA73427@VARK.MIT.EDU> In-Reply-To: <be2f52430501270848132f15c8@mail.gmail.com> References: <41F90140.3020705@trispen.com> <20050127160914.GA72454@VARK.MIT.EDU> <be2f52430501270848132f15c8@mail.gmail.com>
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On Thu, Jan 27, 2005, Jacques Fourie wrote: > Hi, > > Yes, I am trying to patch a piece of code in the kernel. The strange > thing is that this code works without a problem on FreeBSD 4.8 - has > the VM system changed to such an extent between 4.8 and 4.9 that the > pages in the kernel code segment are not writeable anymore? > > Thanks for the bit about the compiler optimization - at least I > understand that part now :) The idea that the compiler is responsible for the different behavior between 4.8 and 4.9 is just a theory, but it really doesn't matter; it's not so easy to dynamically change the code for a function. In addition to the protection bits, you also have to worry about synchronization with calls to that function, and about the possibility that a processor may have the old code in its instruction cache.
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