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= Common parts of GDB and GDBserver (a.k.a., The Stop the Duplication Madness! project) =
<<TableOfContents>>

This page describes the work to eliminate duplicate code of GDB and GDBserver.

== Goal ==
There's a lot of code duplication between GDB and GDBserver. The project has been taking baby steps in reducing such duplication, by refactoring things, converging gdb and gdbserver's designs, and putting shared code in the gdb/common/ directory. The goal of this project is to reduce the duplication as much as possible.

== Where's the duplication then? ==

=== Target backends ===

These are the biggest duplication offenders. That is, the gdb/*-nat.c files and the gdb/gdbserver/*-low.c files accomplish pretty much the same. (Some targets do things differently enough, that they're not really duplication of code, but can be considered different implementations. The Linux support is one such case. Over the years we've been converging them though -- see the [[LocalRemoteFeatureParity]] page for more details.). GDBserver supports fewer target OSs than GDB does. Ideally, we'd finish the [[LocalRemoteFeatureParity]] project first, and then just dump the GDB-side backends. Presently, there's overlap/duplication in:

   * Linux

     See the [[LocalRemoteFeatureParity]] page for more details.

     || GDB || GDBserver ||
     || gdb/linux-nat.c || gdb/gdbserver/linux-low.c ||
     || gdb/proc-service.c || gdb/gdbserver/proc-service.c ||
     || gdb/linux-thread-db.c || gdb/gdbserver/thread-db.c ||
     || ... and related arch specific files ... || ||

   * Windows

     || GDB || GDBserver ||
     || gdb/windows-nat.c || gdb/gdbserver/win32-low.c ||
     || ... and related arch specific files ... || ||

   * NTO

     || GDB || GDBserver ||
     || gdb/nto-procfs.c || gdb/gdbserver/nto-low.c ||
     || ... and related arch specific files ... || ||

=== Arch-specific bits of the target backends ===

Independently of the local/remote parity project, however, there are bits of the backends, most prominently, the arch specific bits, that can be shared between the target backend implementations before then, as the interfaces are similar enough. E.g., code accessing hardware registers, debug registers/watchpoint support; code that detects which variant of a processor the program is running (the xml target description to send to GDB core), etc.. Sharing such arch specific code significantly reduces the effort for new ports (those usually don't need to touch common code). As is today most ports involve doing the same work twice. We should clean up some of the existing ports, laying grounds for good examples for new ports.

Move these duplicated part to common/ directory, and give come up with logically reasonable file names. For example, the code for accessing debug registers are duplicated in gdbserver/i386-low.c and i386-nat.c, so they can be moved to common directory with file name i386-dbg-reg.c and i386-rdbg-reg.h. See [[http://sourceware.org/ml/gdb-patches/2011-03/msg00648.html| Move common macros to i386-dbg-reg.h]].

=== Terminal handling ===

Parts of terminal handling are duplicated.

|| GDB || GDBserver || comments ||
|| gdb/terminal.h || gdb/gdbserver/terminal.h || (parts) ||

=== Event loop machinery ===

|| GDB || GDBserver || comments ||
|| gdb/event-loop.c || gdb/gdbserver/event-loop.c || ||

=== Build/Configure machinery ===

|| GDB || GDBserver || comments ||
|| gdb/configure.ac, etc. || gdb/gdbserver/configure.ac, etc. || ||

So far, we have three possible approaches to address this:

 1. Don't have its own build stuff in common/, let gdb or gdbserver pick the pieces they want, and duplicate the necessary autoconf checks, etc.. This is the status quo.
 2. Make common/ have its own configure. In March 2011, Yao gave a try to build common/ as a library (libcommon.a), for both GDB and GDBserver to link. See the thread [[http://sourceware.org/ml/gdb-patches/2011-02/msg00209.html|here]]. The patches went into CVS, but were later reverted, because of various issues they caused.
 3. Create Makefile fragments and m4 files in common/, then sourced by gdb and gdbserver's build machineries. No new configure. This is the direction we're heading towards now. See [[http://sourceware.org/ml/gdb-patches/2013-04/msg00739.html|this thread (RFC: introduce common.m4)]].
 4. Move gnulib, the common code, and gdbserver to the top-level. Then the configury becomes straightforward.

=== Remote serial protocol ===

|| GDB || GDBserver || comments ||
|| gdb/remote.c || gdb/gdbserver/remote-utils.c || Factor out tohex/fromhex/getpkt/putpkt and more into rsp.c/h ||

== Guidelines ==

=== File Naming ===

  * Avoid "common" in file names in files under common/. Instead, name the files for what they contain, not for the fact that they're "common" to two programs (gdb, gdbserver) presently. If the resulting file is just a dumping ground of miscellaneous things, then call it that. Say, foo-misc.h or foo-defs.h, not foo-common.h. But ... (see below)

=== Split files if possible ===

When moving things to common/, take the opportunity to split them into smaller, more logically atomic, leaner units. E.g., that's how we ended up with ptid.h/ptid.c, instead of inferior-common.h (or some such). Avoid new kitchen sinks! Combining movement and refactoring is bad, but this is just movement: putting code into separate smaller new files is really no different from stuffing it all into one big new file.

----

OngoingWork

LocalRemoteFeatureParity
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None: Common (last edited 2016-01-16 14:43:53 by PedroAlves)

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