Messages in this thread | | | From | Jesse Pollard <> | Subject | Re: Microsoft begining to open source Windows 2000? | Date | Fri, 9 Mar 2001 20:10:50 -0600 |
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On Fri, 09 Mar 2001, Rogier Wolff wrote: >Jesse Pollard wrote: >> On Fri, 09 Mar 2001, Graham Murray wrote: >> >"Mohammad A. Haque" <mhaque@haque.net> writes: >> > >> >> making a patch means you've modfied the source which you are not allowed >> >> to do. The most you can do is report the bug through normal channels >> >> (you dont even have priority in reporting bugs since you have the code). >> > >> >Does making a patch necessarily require modifying the source code? >> >Back in my days as a mainframe systems programmer (ICL VME/B), most OS >> >patches were made to the binary image, either in the file or to the >> >loaded virtual memory image. > >> Nearly always. The problem is that the patch may make the module >> bigger/smaller or relocate variables whose address then changes. All >> locations that these are referenced must be modified (either direct >> address or offset). Sometimes other modules will get relocated too. > >You're too young. Or I'm too old. :-)
Neither - we've both been there. > >IF your patch can be inserted into the code space available: Then good. >If not, you move the code out of the previously allocated space, and >put it somewhere else. Put a "jump" instruction in the old place. >
Only if you generate your patch in assembler.... and there is somewhere else to put the real module...
>At the university there was a lab-assignment where we had to use the >provided semaphore routines. Turns out we found a bug. The TA then >told us it was going to be hard-to-fix, as about 8192 bytes of the 8k >PROM were in use. He was wrong. The bug was one instruction too >many. We just wrote "nop" over the bad instruction. The processor had >also been correctly designed: you could overwrite any instruction in >the PROM with "nop", as the NOP instruction was 0xff. Fixed on the >spot! >
Congratulations - We used to do similar things to change the baud rate of serial interfaces (though overwriting core memory was much easier). -- ------------------------------------------------------------------------- Jesse I Pollard, II Email: jesse@cats-chateau.net
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