From: james.harris.1@gmail.com   
      
   On 09/01/2022 10:44, wolfgang kern wrote:   
   > On 08/01/2022 23:44, James Harris wrote:   
   >> On 08/01/2022 20:10, wolfgang kern wrote:   
   >>   
   >> ...   
   >>   
   >>> Earlier versions of my OS used self-relocation, and they were small   
   >>> enough to fit into the first 640K. Not more since a while ...   
   >> What format did you use for relocatable files? AISI there are two   
   >> choices:   
   >>   
   >> 1. Design your own format. Then relocation would be easy but you'd   
   >> need some way to convert to that form from build tools -   
   >> compiler/assembler - or to produce your own build tools.   
   >>   
   >> 2. Use a predefined format. Then relocation would require parsing the   
   >> structure but (bugs permitting!) it would be easy to produce.   
   >>   
   >>   
   >> FWIW, I am looking to use option 2 ATM but I have all kinds of   
   >> interesting ideas for matters related to option 1. :-)   
   >   
   > My way of self relocation was just one single variable on the very start   
   > of the image in RAM (I put all other rd/wr data anyway 512 bytes upfront   
   > code, similar to a PSP in DOS), so all internal and also external access   
   > just added this to reference anything within code and data by SIB modes.   
      
   I don't get that. If you had instructions like   
      
      mov ebx, [0x7c00]  ;Get pointer from start of image   
      
   then you would need to know where the image started (0x7c00) ... and if   
   you knew where the image started you wouldn't need relocation.   
      
   >   
   > more previous versions used a relative CALL-Null/POP sequence to figure   
   > where it was loaded, but I soon found the better solution as said above.   
      
   I could see value in loading a pointer from a fixed location in memory,   
   e.g.   
      
      mov ebx, [0x1004]  ;Get pointer to globals   
      
   but not from the start of a movable image.   
      
      
      
   --   
   James Harris   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)