(gdbint.info) Overall Structure

 
 Overall Structure
 *****************
 
    GDB consists of three major subsystems: user interface, symbol
 handling (the "symbol side"), and target system handling (the "target
 side").
 
    Ther user interface consists of several actual interfaces, plus
 supporting code.
 
    The symbol side consists of object file readers, debugging info
 interpreters, symbol table management, source language expression
 parsing, type and value printing.
 
    The target side consists of execution control, stack frame analysis,
 and physical target manipulation.
 
    The target side/symbol side division is not formal, and there are a
 number of exceptions.  For instance, core file support involves symbolic
 elements (the basic core file reader is in BFD) and target elements (it
 supplies the contents of memory and the values of registers).  Instead,
 this division is useful for understanding how the minor subsystems
 should fit together.
 
 The Symbol Side
 ===============
 
    The symbolic side of GDB can be thought of as "everything you can do
 in GDB without having a live program running".  For instance, you can
 look at the types of variables, and evaluate many kinds of expressions.
 
 The Target Side
 ===============
 
    The target side of GDB is the "bits and bytes manipulator".  Although
 it may make reference to symbolic info here and there, most of the
 target side will run with only a stripped executable available - or
 even no executable at all, in remote debugging cases.
 
    Operations such as disassembly, stack frame crawls, and register
 display, are able to work with no symbolic info at all.  In some cases,
 such as disassembly, GDB will use symbolic info to present addresses
 relative to symbols rather than as raw numbers, but it will work either
 way.
 
 Configurations
 ==============
 
    "Host" refers to attributes of the system where GDB runs.  "Target"
 refers to the system where the program being debugged executes.  In
 most cases they are the same machine, in which case a third type of
 "Native" attributes come into play.
 
    Defines and include files needed to build on the host are host
 support.  Examples are tty support, system defined types, host byte
 order, host float format.
 
    Defines and information needed to handle the target format are target
 dependent.  Examples are the stack frame format, instruction set,
 breakpoint instruction, registers, and how to set up and tear down the
 stack to call a function.
 
    Information that is only needed when the host and target are the
 same, is native dependent.  One example is Unix child process support;
 if the host and target are not the same, doing a fork to start the
 target process is a bad idea.  The various macros needed for finding the
 registers in the `upage', running `ptrace', and such are all in the
 native-dependent files.
 
    Another example of native-dependent code is support for features that
 are really part of the target environment, but which require `#include'
 files that are only available on the host system.  Core file handling
 and `setjmp' handling are two common cases.
 
    When you want to make GDB work "native" on a particular machine, you
 have to include all three kinds of information.
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