文档介绍：Linker Overview
Linker Overview
- The primary purpose of a linker is to produce an file which can be
executed by an operating system.
- In DOS, executable e in three flavors:
"EXE" files
"COM" files
"SYS" files
- The input to the es from module(s) called translator
modules.
- Individual translator modules can be stored in "OBJ" files. "OBJ"
files are produce by language translators such as assemblers and
compilers.
- Libraries of translator modules can be stored in "LIB" files which
are produced by a librarian from either "OBJ" files or other "LIB"
files.
- A linker can process translator modules from either "OBJ" or "LIB"
files, but at least one module must e from an "OBJ" file.
- All translator modules from "OBJ" files will be included in the
executable file, but only modules which resolve e from
"LIB" files.
_
Comparison of Executable Files
- "EXE" files have a header which contains relocation and other
information which permit "EXE" files to have multiple segments.
This header sets "EXE" files apart from the other executable file
types. Programs are written starting at address 0 (relative to
where the program is loaded in memory).
- "COM" files have no header. "COM" files are written starting a
address 100H because the "COM" file is loaded immediately after the
program segment prefix (PSP) which is 100H bytes long. At the start
of the program, the CS and DS segment registers point to the PSP.
"EXE" files which have an empty relocation table can be converted to
"COM" files by the "EXE2BIN" program.
- "SYS" files are more closely related to "COM" files than "EXE"
files. "SYS" files are loaded once at DOS initialization time.
Since there is no PSP, the programs are written starting at address
0. However, like "COM" files, "SYS" files must have an empty
relocation table.
Contents of Executable Files
"EXE" files "SYS" files
谀哪哪哪哪哪哪哪哪目谀哪哪哪哪哪¿
? "EXE" header ? 砽oad module媚目
媚哪哪哪哪哪哪哪哪拇滥哪哪哪哪哪? ³
? r