[fwd] Submission: Debugging Gnu Objective C with gdb

[Theodore C. Belding]

I've put the patch on the Web at:
http://www-personal.engin.umich.edu/~streak/objc-960812.diff.gz
or you can get it via AFS:
/afs/umich.edu/user/s/t/streak/Public/html/objc-960812.diff.gz
-Ted

>Path:
news.itd.umich.edu!newsxfer2.itd.umich.edu!howland.erols.net!newsfeed.internetmci.com!nntp-hub2.barrnet.net!nntp-hub.barrnet.net!news.NeXT.COM!usenet
>From: address@hidden (Michael Snyder)
>Newsgroups: comp.lang.objective-c
>Subject: Submission: Debugging Gnu Objective C with gdb (0/1)
>Date: 20 Aug 1996 18:22:29 GMT
>Organization: NeXT Software, Inc.
>Lines: 128
>Message-ID: <address@hidden>
>NNTP-Posting-Host: yellow.next.com
>
>
>Since I realized that most people cannot receive the gnu.gdb.bug newsgroup, I  
>thought I would go ahead and post this here too.  This only applies to  
>Objective C programs compiled with GCC and debugged with GDB.
>
>The following patch (sent separately as a uuencoded diff file) should be able  
>to be applied to any gdb source version 4.16 or later.  I have tested these  
>changes on HPUX, Solaris and MS Windows, and I hope they will be portable to  
>other platforms as well (perhaps with a little tweaking).  Here is the README  
>file:
>
>
>GDB Language Support for Objective C
>Submitted by Michael Snyder
>NeXT Software, Inc.
>
>This is a portable implementation of NeXT's gdb support for debugging
>Objective C.  This has only been tested with Gnu's GCC-based Objective
>C compiler, and may not work with other compilers or runtime
>libraries.  It has been tested to a limited extent with the public
>version of GCC and GnuStep, with the majority of the testing being
>done under NeXT's proprietary versions of the compiler and OpenStep.
>It has been tested on Microsoft Windows NT (Gnu and NeXT compilers),
>Solaris (NeXT compiler), and HPUX (NeXT compiler).  I expect it to
>work on other platforms in the Gnu environment, but would not be
>surprised if some tweaking were required.
>
>Language specific features:
> * Auto-recognition of Objective C source code (by the ".m" extension)
> * Demangling of Objective C mangled method names in backtraces etc.
> * Accepts demangled (native) form for Objective C method names
>   for setting breakpoints etc.
> * Understands class scope for instance variables in expressions
>   (automatically dereferences things from the "self" pointer)
> * Step into Objective C message calls
> * Call Objective C methods and print their return values
>   (in native syntax, eg. "print [MyClass myMethod:42]")
> * LIST or BREAK on selectors gives a list of matching implementations
>   (just like what happens with overloaded C++ member functions)
> * Tab-completion on methods and selectors
> * @selector operator
> * INFO CLASS and INFO SELECTOR commands
> * NSString literals in expressions (eg. @"foo")
> * Class names recognised with or without the keyword "struct"
>
>
>
>Auto language recognition:
>Objective C is a first-class language in gdb (just like C++ or
>FORTRAN).  Gdb auto-detects Objective C source files by the ".m"
>extension, enabling name demangling and other language features.
>Should you need to force the current language to Objective C (eg. for
>programs compiled with no symbol information), use:
>         "SET LANGUAGE objective-c".
>
>
>Symbol Demangling:
>Objective C methods names are mangled by GCC into a form that looks
>like (for example) "_i_Classname_Categoryname_Selectorname__" where
>colons (":") in the selector name are replaced with underscores ("_").
>Gdb will reverse this mangling to present the method name as
>"-[Classname(Categoryname) Selectorname::]".  Unfortunately this
>mangling scheme is not uniquely reversable if class, category or
>selector names contain underscores, so gdb will demangle such names
>incorrectly.
>
>
>Native-form Names of Objective C Methods:
>Breakpoint commands etc. can refer to Objective C methods in their
>demangled form:
>        (gdb) BREAK +[Classname Selector:withArg:andArg:]
>
>
>Class scope:
>If you are debugging in an Objective C method of a class that has an
>instance variable (eg. "foo"), you can refer to that variable by name,
>        (gdb) print foo
>without having to refer to it thru the self pointer:
>        (gdb) print self->foo   // C++ analogy: this->foo
>
>
>
>Calls to Objective C Methods in expressions:
>The PRINT and CALL commands can be used to call Objective C methods
>using the native syntax (and print their return values):
>        (gdb) call  [foo withBar: 12 andBaz: 14]
>        (gdb) print $myfoo = [[Foo alloc] init]
>
>
>Selectors treated as overloaded functions:
>The BREAK and LIST commands can take a raw selector as an argument.
>If the selector is implemented by more than one class, gdb will
>present a list of the possible matches, just as it would in the case
>of a C++ overloaded member function.  The user can select one,
>several, or all of the matches from the list.
>        (gdb) break init
>        [0] cancel
>        [1] all
>        [2] -[Change init] at Change.m:20
>        [3] -[ChangeManager init] at ChangeManage.m:30
>        [4] -[DrawApp init] at DrawApp.m:130
>        >
>
>
>INFO CLASS and INFO SELECTOR commands:
>By analogy with the INFO FUNCTION and INFO TYPE commands, these accept
>a regular expression and print a list of Objective C classes or selectors
>that match.
>
>
>NSString literals:
>Many Objective C methods expect an NSString literal as an argument,
>and many expressions that might be cut-and-paste evaluated from an
>Objective C program contain such literals.  As a convenience, GDB
>will accept such a literal, and build an NSString constant in the
>child process address space.
>        (gdb) print [NSImage imageNamed: @"Cross.tiff"]
>
>
>Builtin typedefs for classes:
>As with C++, the Objective C language does not expect you to use
>the keyword "struct" in front of a class name.  However the GCC
>compiler emits the type symbols for classes as structs.  GDB will
>automatically create an internal typedef symbol that might look like:
>        typedef struct NSString NSString;
>so that the user can use casts like "(NSString *) 0" instead of
>having to type "(struct NSString *) 0" (although the later will
>still be accepted too).

--
Ted Belding                        mailto:address@hidden
University of Michigan Program for the Study of Complex Systems
http://www-personal.engin.umich.edu/~streak/