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CPM OPERATING SYSTEMS/CPM 68K/1.0X SOURCES/v101/newlink/spec.doc

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+Description of LINK-68
+.sp 
+.pp 0
+LINK-68 is the new enhanced linker for CP/M-68K.  The major new feature is 
+the ability to link overlayed programs. 
+.sp 2
+1.  Overlay Scheme
+.pp
+LINK-68 supports a simple tree-structured overlay scheme.  Only one overlay 
+from a given level is memory-resident at a time.  An overlay can 
+reference a symbol in a direct descendant or in any ancestor.  An  
+overlay cannot reference a symbol in a sibling overlay or in an overlay 
+more than one level down in the tree.  
+.pp
+The lowest allowed level is five levels below the root.  The maximum 
+number of overlays is 255.
+.pp
+All global static data is in the root, no matter where it is originally 
+defined.
+.sp 2
+2.  Command Line
+.pp
+The command line for LINK-68 has almost the same format as for LINK-86, as 
+described in sections 7 and 8 of the Programmer's Utilities Guide 
+for CP/M-86.  The main differences are in the available options.  The 
+format for specifying options and overlay structures is the same.  Parens 
+enclose overlay specifications, and square brackets enclose options.
+.pp 
+Anything after a backslash on a command line is ignored.
+.pp
+If you just type 'LINK68' without any command line, the linker lists the 
+options.  The following is a list of the options for LINK-68.  
+.pp
+ABSOLUTE
+.pp
+.in 5
+Tells the linker to generate an absolute file 
+with no relocation bits.  The default is a relocatable program.
+.pp
+.ti -5
+ALLMODS
+.pp
+All modules from a library are loaded, whether or not they are referenced.  
+The default is to only load referenced library modules.
+.pp
+.ti -5
+BSSBASE
+.pp
+Sets the base for the uninitialized data segment in discontiguous 
+programs.  The default value is 
+the first even word after the DATA segment.  This option is not 
+allowed when linking overlayed programs.
+.pp
+.ti -5
+COMMAND
+.pp
+Specifies that the following named file contains 
+the rest of the command line.  
+The linker ignores the rest of the main command line and does not return 
+to it.  Nested command files are not allowed.
+.pp
+.ti -5
+DATABASE
+.pp
+Specifies the start of the DATA segment in discontiguous programs.  The 
+default is the first even word after the TEXT segment.  This option 
+is not allowed when linking overlayed programs.
+.pp
+.ti-5
+IGNORE
+.pp
+Ignore 16-bit address overflow.  This is like the -i option in LO68.
+.pp
+.ti -5
+INCLUDE
+.pp
+Instructs the linker to load an unreferenced module from a 
+library.  The format for this option is:
+.sp
+.ti 10
+filename [INCLUDE [module name]]
+.pp
+.ti -5
+LOCALS
+.pp
+Tells the linker to put local symbols in the symbol table.  The default is 
+no local symbols.  This option only applies from the point in the command 
+line that it appears.  The NOLOCALS switch turns this option off.  Use them 
+in combination to put local symbols from specific files in the symbol table.
+.pp
+Local symbols starting with 'L' are always ignored.
+.pp
+.ti -5
+NOLOCALS
+.pp
+See LOCAL.
+.pp
+.ti-5
+SYMBOLS
+.pp
+Put the symbol table in the output file.  The default is no symbol table.
+.pp
+.ti -5
+TEMPFILES
+.pp
+Specifies the drive to use for temporary files.  The default is the 
+currently logged-in drive.  This option must preceed any input files on 
+the command line.
+.pp
+.ti -5
+TEXTBASE
+.pp
+Specifies the base for the TEXT segment.  The default is 0.  This option 
+is allowed with overlayed programs, but the DATABASE and BSSBASE options 
+are not allowed when linking overlayed programs.
+.in 0
+.sp 
+.pp
+The following are examples of command lines for LINK-68.  Notice that an 
+option name can be abreviated to its shortest unambiguous form.  Addresses 
+are always in hex.
+.in 5
+.sp
+.nf
+LINK68 [SYM, TEM[D:] FOOBAZ = FOOMAIN, FOOLIB 
+.SP
+LINK68 [COM[INP.JNK	\\ CLOSING BRACKETS ARE NOT NEEDED 
+.sp
+LINK68 [ABS, TEX[500]] P.68K = ST.O,P.O[LO],LIB.A[NOL],(V1.O),(V2.O)
+.fi
+.in 0
+.sp 2
+3.  Format of an Overlay File
+.pp
+An overlay file has the same format as a regular a.out-format file.  The 
+header "magic" word is always 601AH.  The file can be either absolute or 
+relocatable.  The overlay's symbols are in the root file, if the SYMBOLS 
+options is used.
+.pp
+An overlay file can have any type, but the default type is O68.
+.pp
+To specify that a block of BSS space is to be in the root instead of in the 
+overlay's BSS segment, generate an external symbol for the space and give 
+the symbol a value equal to the number of bytes required.  The space will 
+be allocated on an even boundary in the root's BSS segment.  If more than 
+one module specify static storage with the same name, the largest size is 
+used for allocation.
+.pp
+The BSS size for the root file is set to contain the area into which the 
+overlays are loaded.  The symbol _end is resolved to the top of the 
+overlay area. 
+.sp 2
+4.  Overlay Manager
+.pp
+The overlay manager should be transparent to your program, except for the 
+time required to read in the overlay.  Write the modules as if you were 
+going to load everything in one file.  Make sure to include the files 
+containing the overlay handler and loader in the root.
+
+
+
+