- revert one change (which requires CVS, post-6.1 gdb)

[packages/gdb.git] / gdb-ada-support.patch

From gdb-patches-return-33877-listarch-gdb-patches=sources dot redhat dot com at sources dot redhat dot com Wed Jun 16 08:42:53 2004
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From: Paul Hilfinger <hilfingr at gnat dot com>
To: gdb-patches at sources dot redhat dot com
Cc: drow at false dot org, jimb at redhat dot com, eliz at gnu dot org
In-reply-to: <20040609131240 dot GA7587 at nevyn dot them dot org> (message from Daniel
        Jacobowitz on Wed, 9 Jun 2004 09:12:40 -0400)
Subject: Re: [RFA]: Turn on Ada support, take 2
References: <20040608090758.C59CAF2940@nile.gnat.com> <vt2aczd8aah.fsf@zenia.home> <20040609131240.GA7587@nevyn.them.org>
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Date: Wed, 16 Jun 2004 04:42:37 -0400 (EDT)
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Here is an update to the patch I sent previously.  In this version, I have

1. Removed the compilation of ada-tasks.o, since we have not yet turned
   on any of it in the public version.

2. Responded to most of Eli's comments.  I will have to consider the
   issue of formating things like 'Address, since the standard rendering
   in info files provided by the technically appropriate marker, 
   @code, looks rather bad (in my opinion), due to the adjacent quotes 
   at the beginning.  

A previous patch to the Ada sources added some conditionalization to mark code
that is not yet used in the public version (for the benefit of reviewers).


ChangeLogs:

 2004-06-16  Paul N. Hilfinger  <Hilfinger@gnat.com>

        Turn on initial Ada support (mainly expression evaluation).
        
        * Makefile.in (ada_lex_c): Define
        (HFILES_NO_SRCDIR): Add ada-lang.h.
        (COMMON_OBS): Add ada-lang.o, ada-typeprint.o, ada-valprint.o.
        (YYOBJ): Add ada-exp.o.
        (rule .l.c): Generalize to not mention ada.
        (ada-lex.o): Remove (ada-lex.c is included by ada-exp.y).
        (ada-lang.o): Add dependencies on completer.h, gdb_obstack.h, 
        hashtab.h.
        (ada-tasks.o): Add dependency on gdb_string.h.
        (ada-valprint.o): Add dependency on gdb_string.h.
        
        * symtab.c: Add dependency on ada-lang.h.
        (symbol_natural_name): Add Ada case.
        (symbol_demangled_name): Add Ada case.
        (symbol_search_name): Add Ada case.
        
        * symfile.c (init_filename_language_table): Add extensions for
        Ada.
        
        * defs.h (enum language): Add language_ada.

        * gdbtypes.h (TYPE_FLAG_FIXED_INSTANCE): Define.
        
2004-06-09  Paul N. Hilfinger  <hilfinger@gnat.com>

        * doc/gdb.texinfo (Filenames): Add Ada suffixes.
        (Ada) New section.



Index: gdb/Makefile.in
===================================================================
RCS file: /cvs/src/src/gdb/Makefile.in,v
retrieving revision 1.587
diff -u -p -r1.587 Makefile.in
--- gdb/Makefile.in     14 Jun 2004 20:40:39 -0000      1.587
+++ gdb/Makefile.in     16 Jun 2004 08:23:45 -0000
@@ -616,6 +616,7 @@ nm_h =              @nm_h@
 # gdb/ headers
 #
 
+ada_lex_c = ada-lex.c
 ada_lang_h = ada-lang.h $(value_h) $(gdbtypes_h)
 alphabsd_tdep_h = alphabsd-tdep.h
 alpha_tdep_h = alpha-tdep.h
@@ -833,7 +834,7 @@ HFILES_NO_SRCDIR = bcache.h buildsym.h c
        symfile.h symfile-mem.h stabsread.h target.h terminal.h typeprint.h \
        xcoffsolib.h \
        macrotab.h macroexp.h macroscope.h \
-       c-lang.h f-lang.h \
+       ada-lang.h c-lang.h f-lang.h \
        jv-lang.h \
        m2-lang.h  p-lang.h \
        complaints.h valprint.h \
@@ -894,7 +895,7 @@ COMMON_OBS = $(DEPFILES) $(YYOBJ) \
        dbxread.o coffread.o coff-pe-read.o elfread.o \
        dwarfread.o dwarf2read.o mipsread.o stabsread.o corefile.o \
        dwarf2expr.o dwarf2loc.o dwarf2-frame.o \
-       c-lang.o f-lang.o objc-lang.o \
+       ada-lang.o c-lang.o f-lang.o objc-lang.o \
        ui-out.o cli-out.o \
        varobj.o wrapper.o \
        jv-lang.o jv-valprint.o jv-typeprint.o \
@@ -902,8 +903,8 @@ COMMON_OBS = $(DEPFILES) $(YYOBJ) \
        scm-exp.o scm-lang.o scm-valprint.o \
        sentinel-frame.o \
        complaints.o typeprint.o \
-       c-typeprint.o f-typeprint.o m2-typeprint.o \
-       c-valprint.o cp-valprint.o f-valprint.o m2-valprint.o \
+       ada-typeprint.o c-typeprint.o f-typeprint.o m2-typeprint.o \
+       ada-valprint.o c-valprint.o cp-valprint.o f-valprint.o m2-valprint.o \
        nlmread.o serial.o mdebugread.o top.o utils.o \
        ui-file.o \
        user-regs.o \
@@ -927,6 +928,7 @@ YYFILES = c-exp.c \
        f-exp.c m2-exp.c p-exp.c
 YYOBJ = c-exp.o \
        objc-exp.o \
+       ada-exp.o \
        jv-exp.o \
        f-exp.o m2-exp.o p-exp.o
 
@@ -1495,7 +1497,7 @@ valprint.o: $(srcdir)/valprint.c
            echo $(FLEX) -Isit $< ">" $@; \
            $(FLEX) -Isit $< > $@; \
        elif [ ! -f $@ -a ! -f $< ]; then \
-           echo "ada-lex.c missing and flex not available."; \
+           echo "$< missing and flex not available."; \
            false; \
        elif [ ! -f $@ ]; then \
            echo "Warning: $*.c older than $*.l and flex not available."; \
@@ -1522,18 +1524,18 @@ ada-lang.o: ada-lang.c $(gdb_string_h) $
        $(gdbtypes_h) $(gdbcmd_h) $(expression_h) $(parser_defs_h) \
        $(language_h) $(c_lang_h) $(inferior_h) $(symfile_h) $(objfiles_h) \
        $(breakpoint_h) $(gdbcore_h) $(ada_lang_h) $(ui_out_h) $(block_h) \
-       $(infcall_h) $(dictionary_h)
-ada-lex.o: ada-lex.c
+       $(completer_h) $(infcall_h) $(gdb_obstack_h) $(dictionary_h) \
+       $(hashtab_h)
 ada-tasks.o: ada-tasks.c $(defs_h) $(command_h) $(value_h) $(language_h) \
        $(inferior_h) $(symtab_h) $(target_h) $(regcache_h) $(gdbcore_h) \
-       $(gregset_h) $(ada_lang_h)
+       $(gregset_h) $(gdb_string_h) $(ada_lang_h)
 ada-typeprint.o: ada-typeprint.c $(defs_h) $(gdb_obstack_h) $(bfd_h) \
        $(symtab_h) $(gdbtypes_h) $(expression_h) $(value_h) $(gdbcore_h) \
        $(target_h) $(command_h) $(gdbcmd_h) $(language_h) $(demangle_h) \
        $(c_lang_h) $(typeprint_h) $(ada_lang_h) $(gdb_string_h)
 ada-valprint.o: ada-valprint.c $(defs_h) $(symtab_h) $(gdbtypes_h) \
        $(expression_h) $(value_h) $(demangle_h) $(valprint_h) $(language_h) \
-       $(annotate_h) $(ada_lang_h) $(c_lang_h) $(infcall_h)
+       $(annotate_h) $(ada_lang_h) $(c_lang_h) $(gdb_string_h) $(infcall_h)
 aix-thread.o: aix-thread.c $(defs_h) $(gdb_assert_h) $(gdbthread_h) \
        $(target_h) $(inferior_h) $(regcache_h) $(gdbcmd_h) $(language_h) \
        $(ppc_tdep_h) $(gdb_string_h)
Index: gdb/defs.h
===================================================================
RCS file: /cvs/src/src/gdb/defs.h,v
retrieving revision 1.147
diff -u -p -r1.147 defs.h
--- gdb/defs.h  10 Jun 2004 20:05:43 -0000      1.147
+++ gdb/defs.h  16 Jun 2004 08:23:45 -0000
@@ -220,6 +220,7 @@ enum language
     language_asm,              /* Assembly language */
     language_scm,              /* Scheme / Guile */
     language_pascal,           /* Pascal */
+    language_ada,              /* Ada */
     language_minimal           /* All other languages, minimal support only */
   };
 
Index: gdb/gdbtypes.h
===================================================================
RCS file: /cvs/src/src/gdb/gdbtypes.h,v
retrieving revision 1.53
diff -u -p -r1.53 gdbtypes.h
--- gdb/gdbtypes.h      2 Jun 2004 21:01:55 -0000       1.53
+++ gdb/gdbtypes.h      16 Jun 2004 08:23:45 -0000
@@ -273,6 +273,17 @@ enum type_code
 #define TYPE_ADDRESS_CLASS_ALL(t) (TYPE_INSTANCE_FLAGS(t) \
                                   & TYPE_FLAG_ADDRESS_CLASS_ALL)
 
+/* The debugging formats (especially STABS) do not contain enough information
+   to represent all Ada types---especially those whose size depends on
+   dynamic quantities.  Therefore, the GNAT Ada compiler includes
+   extra information in the form of additional type definitions
+   connected by naming conventions.  This flag indicates that the 
+   type is an ordinary (unencoded) GDB type that has been created from 
+   the necessary run-time information, and does not need further 
+   interpretation. Optionally marks ordinary, fixed-size GDB type. */
+
+#define TYPE_FLAG_FIXED_INSTANCE (1 << 15)
+
 /*  Array bound type.  */
 enum array_bound_type
 {
Index: gdb/symfile.c
===================================================================
RCS file: /cvs/src/src/gdb/symfile.c,v
retrieving revision 1.132
diff -u -p -r1.132 symfile.c
--- gdb/symfile.c       15 Jun 2004 01:04:20 -0000      1.132
+++ gdb/symfile.c       16 Jun 2004 08:23:46 -0000
@@ -2158,6 +2158,10 @@ init_filename_language_table (void)
       add_filename_language (".pas", language_pascal);
       add_filename_language (".p", language_pascal);
       add_filename_language (".pp", language_pascal);
+      add_filename_language (".adb", language_ada);
+      add_filename_language (".ads", language_ada);
+      add_filename_language (".a", language_ada);
+      add_filename_language (".ada", language_ada);
     }
 }
 
Index: gdb/symtab.c
===================================================================
RCS file: /cvs/src/src/gdb/symtab.c,v
retrieving revision 1.132
diff -u -p -r1.132 symtab.c
--- gdb/symtab.c        10 Jun 2004 20:05:44 -0000      1.132
+++ gdb/symtab.c        16 Jun 2004 08:23:47 -0000
@@ -41,6 +41,7 @@
 #include "source.h"
 #include "filenames.h"         /* for FILENAME_CMP */
 #include "objc-lang.h"
+#include "ada-lang.h"
 
 #include "hashtab.h"
 
@@ -632,17 +633,24 @@ symbol_init_demangled_name (struct gener
 char *
 symbol_natural_name (const struct general_symbol_info *gsymbol)
 {
-  if ((gsymbol->language == language_cplus
-       || gsymbol->language == language_java
-       || gsymbol->language == language_objc)
-      && (gsymbol->language_specific.cplus_specific.demangled_name != NULL))
+  switch (gsymbol->language) 
     {
-      return gsymbol->language_specific.cplus_specific.demangled_name;
-    }
-  else
-    {
-      return gsymbol->name;
+    case language_cplus:
+    case language_java:
+    case language_objc:
+      if (gsymbol->language_specific.cplus_specific.demangled_name != NULL)
+       return gsymbol->language_specific.cplus_specific.demangled_name;
+      break;
+    case language_ada:
+      if (gsymbol->language_specific.cplus_specific.demangled_name != NULL)
+       return gsymbol->language_specific.cplus_specific.demangled_name;
+      else
+       return ada_decode_symbol (gsymbol);
+      break;
+    default:
+      break;
     }
+  return gsymbol->name;
 }
 
 /* Return the demangled name for a symbol based on the language for
@@ -650,13 +658,24 @@ symbol_natural_name (const struct genera
 char *
 symbol_demangled_name (struct general_symbol_info *gsymbol)
 {
-  if (gsymbol->language == language_cplus
-      || gsymbol->language == language_java
-      || gsymbol->language == language_objc)
-    return gsymbol->language_specific.cplus_specific.demangled_name;
-
-  else 
-    return NULL;
+  switch (gsymbol->language) 
+    {
+    case language_cplus:
+    case language_java:
+    case language_objc:
+      if (gsymbol->language_specific.cplus_specific.demangled_name != NULL)
+       return gsymbol->language_specific.cplus_specific.demangled_name;
+      break;
+    case language_ada:
+      if (gsymbol->language_specific.cplus_specific.demangled_name != NULL)
+       return gsymbol->language_specific.cplus_specific.demangled_name;
+      else
+       return ada_decode_symbol (gsymbol);
+      break;
+    default:
+      break;
+    }
+  return NULL;
 }
 
 /* Return the search name of a symbol---generally the demangled or
#### gdb post-6.1 branch
##@@ -664,7 +683,10 @@ symbol_demangled_name (struct general_sy
##    If there is no distinct demangled name, then returns the same value 
##    (same pointer) as SYMBOL_LINKAGE_NAME. */
## char *symbol_search_name (const struct general_symbol_info *gsymbol) {
##-  return symbol_natural_name (gsymbol);
##+  if (gsymbol->language == language_ada)
##+    return gsymbol->name;
##+  else
##+    return symbol_natural_name (gsymbol);
## }
## 
## /* Initialize the structure fields to zero values.  */
##
Index: gdb/doc/gdb.texinfo
===================================================================
RCS file: /cvs/src/src/gdb/doc/gdb.texinfo,v
retrieving revision 1.206
diff -u -p -r1.206 gdb.texinfo
--- gdb/doc/gdb.texinfo 14 Jun 2004 22:26:33 -0000      1.206
+++ gdb/doc/gdb.texinfo 16 Jun 2004 08:23:53 -0000
@@ -7741,6 +7741,11 @@ If a source file name ends in one of the
 @value{GDBN} infers that its language is the one indicated.
 
 @table @file
+@item .ada
+@itemx .ads
+@itemx .adb
+@itemx .a
+Ada source file.
 
 @item .c
 C source file
@@ -8031,7 +8036,7 @@ being set automatically by @value{GDBN}.
 @node Support
 @section Supported languages
 
-@value{GDBN} supports C, C@t{++}, Objective-C, Fortran, Java, assembly, and Modula-2.
+@value{GDBN} supports C, C@t{++}, Objective-C, Fortran, Java, assembly, Modula-2, and Ada.
 @c This is false ...
 Some @value{GDBN} features may be used in expressions regardless of the
 language you use: the @value{GDBN} @code{@@} and @code{::} operators,
@@ -8051,6 +8056,7 @@ language reference or tutorial.
 * C::                           C and C@t{++}
 * Objective-C::                 Objective-C
 * Modula-2::                    Modula-2
+* Ada::                         Ada
 @end menu
 
 @node C
@@ -8666,7 +8672,7 @@ the description of an object.  However, 
 with certain Objective-C libraries that have a particular hook
 function, @code{_NSPrintForDebugger}, defined.
 
-@node Modula-2,  , Objective-C, Support
+@node Modula-2, Ada, Objective-C, Support
 @subsection Modula-2
 
 @cindex Modula-2, @value{GDBN} support
@@ -9109,6 +9115,481 @@ address can be specified by an integral 
 In @value{GDBN} scripts, the Modula-2 inequality operator @code{#} is
 interpreted as the beginning of a comment.  Use @code{<>} instead.
 
+@node Ada
+@subsection Ada
+@cindex Ada
+
+The extensions made to @value{GDBN} for Ada only support
+output from the @sc{gnu} Ada (GNAT) compiler.
+Other Ada compilers are not currently supported, and
+attempting to debug executables produced by them is most likely
+to be difficult.
+
+
+@cindex expressions in Ada
+@menu
+* Ada Mode Intro::              General remarks on the Ada syntax 
+                                   and semantics supported by Ada mode 
+                                   in @value{GDBN}
+* Omissions from Ada::          Restrictions on the Ada expression syntax.
+* Additions to Ada::            Extensions of the Ada expression syntax.
+* Stopping Before Main Program:: Debugging the program during elaboration.
+* Ada Exceptions::              Setting breakpoints on exception handlers.
+* Ada Generic Units::           Dealing with generic instantiations.
+* Ada Glitches::                Known peculiarities of Ada mode.
+@end menu
+
+@node Ada Mode Intro
+@subsubsection Introduction
+@cindex Ada mode, general
+
+The Ada mode of @value{GDBN} supports a fairly large subset of Ada expression 
+syntax, with some extensions.
+The philosophy behind the design of this subset is 
+
+@itemize @bullet
+@item
+That @value{GDBN} should provide basic literals and access to operations for 
+arithmetic, dereferencing, field selection, indexing, and subprogram calls, 
+leaving more sophisticated computations to subprograms written into the
+program (which therefore may be called from @value{GDBN}).
+
+@item 
+That type safety and strict adherence to Ada language restrictions
+are not particularly important to the @value{GDBN} user.
+
+@item 
+That brevity is important to the @value{GDBN} user.
+@end itemize
+
+Thus, for brevity, the debugger acts as if there were 
+implicit @code{with} and @code{use} clauses in effect for all user-written 
+packages, making it unnecessary to fully qualify most names with 
+their packages, regardless of context.  Where this causes ambiguity, 
+@value{GDBN} asks the user's intent.
+
+The debugger will start in Ada mode if it detects an Ada main program. 
+As for other languages, it will enter Ada mode when stopped in a program that
+was translated from an Ada source file.
+
+While in Ada mode, you may use `@t{--}' for comments.  This is useful 
+mostly for documenting command files.  The standard @value{GDBN} comment 
+(@samp{#}) still works at the beginning of a line in Ada mode, but not in the 
+middle (to allow based literals).
+
+The debugger supports limited overloading.  Given a subprogram call in which
+the function symbol has multiple definitions, it will use the number of 
+actual parameters and some information about their types to attempt to narrow
+the set of definitions.  It also makes very limited use of context, preferring
+procedures to functions in the context of the @code{call} command, and
+functions to procedures elsewhere. 
+
+@node Omissions from Ada
+@subsubsection Omissions from Ada
+@cindex Ada, omissions from
+
+Here are the notable omissions from the subset:
+
+@itemize @bullet
+@item
+Only a subset of the attributes are supported:
+
+@itemize @minus
+@item
+@t{'First}, @t{'Last}, and @t{'Length}
+ on array objects (not on types and subtypes).
+
+@item
+@t{'Min} and @t{'Max}.  
+
+@item 
+@t{'Pos} and @t{'Val}. 
+
+@item
+@t{'Tag}.
+
+@item
+@t{'Range} on array objects (not subtypes), but only as the right
+operand of the membership (@code{in}) operator.
+
+@item 
+@t{'Access}, @t{'Unchecked_Access}, and 
+@t{'Unrestricted_Access} (a GNAT extension).
+
+@item
+@t{'Address}.
+@end itemize
+
+@item
+The names in
+@code{Characters.Latin_1} are not available and
+concatenation is not implemented.  Thus, escape characters in strings are 
+not currently available.
+
+@item
+Equality tests (@samp{=} and @samp{/=}) on arrays test for bitwise
+equality of representations.  They will generally work correctly
+for strings and arrays whose elements have integer or enumeration types.
+They may not work correctly for arrays whose element
+types have user-defined equality, for arrays of real values 
+(in particular, IEEE-conformant floating point, because of negative
+zeroes and NaNs), and for arrays whose elements contain unused bits with
+indeterminate values.  
+
+@item
+The other component-by-component array operations (@code{and}, @code{or}, 
+@code{xor}, @code{not}, and relational tests other than equality)
+are not implemented. 
+
+@item 
+There are no record or array aggregates.
+
+@item
+Dispatching subprogram calls are not implemented.
+
+@item
+The overloading algorithm is much more limited (i.e., less selective)
+than that of real Ada.  It makes only limited use of the context in which a subexpression
+appears to resolve its meaning, and it is much looser in its rules for allowing
+type matches.  As a result, some function calls will be ambiguous, and the user
+will be asked to choose the proper resolution.
+
+@item
+The @code{new} operator is not implemented.
+
+@item
+Entry calls are not implemented.
+
+@item 
+Aside from printing, arithmetic operations on the native VAX floating-point 
+formats are not supported.
+
+@item
+It is not possible to slice a packed array.
+@end itemize
+
+@node Additions to Ada
+@subsubsection Additions to Ada
+@cindex Ada, deviations from 
+
+As it does for other languages, @value{GDBN} makes certain generic
+extensions to Ada (@pxref{Expressions}):
+
+@itemize @bullet
+@item
+If the expression @var{E} is a variable residing in memory 
+(typically a local variable or array element) and @var{N} is 
+a positive integer, then @code{@var{E}@@@var{N}} displays the values of
+@var{E} and the @var{N}-1 adjacent variables following it in memory as an array.  
+In Ada, this operator is generally not necessary, since its prime use
+is in displaying parts of an array, and slicing will usually do this in Ada.
+However, there are occasional uses when debugging programs
+in which certain debugging information has been optimized away.
+
+@item
+@code{@var{B}::@var{var}} means ``the variable named @var{var} that appears
+in function or file @var{B}.''  When @var{B} is a file name, you must typically
+surround it in single quotes.
+
+@item 
+The expression @code{@{@var{type}@} @var{addr}} means ``the variable of type
+@var{type} that appears at address @var{addr}.''
+
+@item
+A name starting with @samp{$} is a convenience variable 
+(@pxref{Convenience Vars}) or a machine register (@pxref{Registers}).
+@end itemize
+
+In addition, @value{GDBN} provides a few other shortcuts and outright additions specific 
+to Ada:
+
+@itemize @bullet
+@item 
+The assignment statement is allowed as an expression, returning
+its right-hand operand as its value.  Thus, you may enter
+
+@smallexample
+set x := y + 3
+print A(tmp := y + 1)
+@end smallexample
+
+@item 
+The semicolon is allowed as an ``operator,''  returning as its value 
+the value of its right-hand operand.
+This allows, for example,
+complex conditional breaks:
+
+@smallexample
+break f
+condition 1 (report(i); k += 1; A(k) > 100)
+@end smallexample
+
+@item 
+Rather than use catenation and symbolic character names to introduce special 
+characters into strings, one may instead use a special bracket notation, 
+which is also used to print strings.  A sequence of characters of the form 
+@samp{["@var{XX}"]} within a string or character literal denotes the 
+(single) character whose numeric encoding is @var{XX} in hexadecimal.  The
+sequence of characters @samp{["""]} also denotes a single quotation mark 
+in strings.   For example,
+@smallexample
+   "One line.["0a"]Next line.["0a"]"
+@end smallexample
+@noindent
+Contains an ASCII newline character (@code{Ada.Characters.Latin_1.LF}) after each
+period.
+
+@item
+The subtype used as a prefix for the attributes @t{'Pos}, @t{'Min}, and
+@t{'Max} is optional (and is ignored in any case).  For example, it is valid
+to write
+
+@smallexample
+print 'max(x, y)
+@end smallexample
+
+@item
+When printing arrays, @value{GDBN} uses positional notation when the 
+array has a lower bound of 1, and uses a modified named notation otherwise.
+For example, a one-dimensional array of three integers with a lower bound of 3 might print as
+
+@smallexample
+(3 => 10, 17, 1)
+@end smallexample
+
+@noindent
+That is, in contrast to valid Ada, only the first component has a @code{=>} 
+clause.
+
+@item
+You may abbreviate attributes in expressions with any unique,
+multi-character subsequence of 
+their names (an exact match gets preference).
+For example, you may use @t{a'len}, @t{a'gth}, or @t{a'lh}
+in place of  @t{a'length}.
+
+@item
+@cindex quoting Ada internal identifiers
+Since Ada is case-insensitive, the debugger normally maps identifiers you type 
+to lower case.  The GNAT compiler uses upper-case characters for 
+some of its internal identifiers, which are normally of no interest to users.
+For the rare occasions when you actually have to look at them,
+enclose them in angle brackets to avoid the lower-case mapping. 
+For example,
+@smallexample
+(gdb) print <JMPBUF_SAVE>[0]
+@end smallexample
+
+@item
+Printing an object of class-wide type or dereferencing an 
+access-to-class-wide value will display all the components of the object's
+specific type (as indicated by its run-time tag).  Likewise, component
+selection on such a value will operate on the specific type of the
+object.
+
+@end itemize
+
+@node Stopping Before Main Program
+@subsubsection Stopping at the Very Beginning
+
+@cindex breakpointing Ada elaboration code
+It is sometimes necessary to debug the program during elaboration, and
+before reaching the main procedure.
+As defined in the Ada Reference
+Manual, the elaboration code is invoked from a procedure called
+@code{adainit}.  To run your program up to the beginning of
+elaboration, simply use the following two commands:
+@code{tbreak adainit} and @code{run}.
+
+@node Ada Exceptions
+@subsubsection Breaking on Ada Exceptions
+@cindex Ada, exceptions
+
+In Ada mode, you can set breakpoints that trip when your program raises 
+selected exceptions.
+
+@table @code
+@kindex break exception
+@item break exception
+Set a breakpoint that trips whenever (any task in the) program raises
+any exception.
+
+@item break exception @var{name}
+Set a breakpoint that trips whenever (any task in the) program raises
+the exception @var{name}.
+
+When inserting a breakpoint on a specific exception for which an
+homonym entity exists in the application, it is necessary to prefix
+the exception name with its package name.  In particular, if an entity
+sharing the same name as one of the standard exceptions has been defined,
+the exception name must be prefixed with package @code{Standard} when
+setting a breakpoint on this exception.
+
+@smallexample
+@iftex
+@leftskip=0.5cm
+@end iftex
+(gdb) break exception Standard.Constraint_Error
+@end smallexample
+
+@item break exception unhandled
+Set a breakpoint that trips whenever (any task in the) program raises an
+exception for which there is no handler.
+At the moment, 
+depending on the implementation of exceptions used on your platform, 
+this may not have quite the desired effect.  Other forms of
+exception breaking stop the program at the point the exception is raised.
+In Ada implementations that use setjmp and longjmp to implement exception
+handling, however, unhandled exceptions are not detected until the 
+affected task's stack is completely unwound.  Thus, you find out that a
+task has terminated with an exception, but you aren't told where it was
+raised.
+
+@kindex info exceptions
+@item info exceptions 
+@itemx info exceptions @var{regexp}
+The @code{info exceptions} command permits the user to examine all defined
+exceptions within Ada programs.  With a regular expression, @var{regexp}, as 
+argument, prints out only those exceptions whose name matches @var{regexp}.
+@end table
+
+@node Ada Generic Units
+@subsubsection Debugging Generic Units
+@cindex Ada, generic units
+
+GNAT always uses code expansion for generic instantiation.  This means that
+each time an instantiation occurs, a complete copy of the original code is
+made with appropriate substitutions.
+
+It is not possible to refer to the original generic entities themselves
+in @value{GDBN} (there is no code to refer to), but it
+is certainly possible to debug a particular instance of a generic, simply by
+using the appropriate expanded names.  For example, suppose that 
+@code{Gen} is a generic package:
+
+@smallexample
+-- In file gen.ads:
+generic package Gen is
+   function F (v1 : Integer) return Integer;
+end Gen;
+
+-- In file gen.adb:
+package body Gen is
+   function F (v1 : Integer) return Integer is
+   begin
+      return v1+1;         -- Line 5
+   end F;
+end Gen;
+@end smallexample
+
+@noindent
+and we have the following expansions
+
+@smallexample
+with Gen;
+procedure G is
+   package Gen1 is new Gen;
+   package Gen2 is new Gen;
+
+   I : Integer := 0;
+begin
+   I := Gen1.F (I);
+   I := Gen2.F (I);
+   I := Gen1.F (I);
+   I := Gen2.F (I);
+end;
+@end smallexample
+
+@noindent
+Then to break on a call to procedure @code{F} in the @code{Gen2} instance, simply
+use the command:
+
+@smallexample
+break G.Gen2.F
+@end smallexample
+
+When a breakpoint occurs, you can step through the code of the generic
+instance in the normal manner.  You can also examine values of data in the
+normal manner, providing the appropriate generic package qualification to
+refer to non-local entities.
+
+@node Ada Glitches
+@subsubsection Known Peculiarities of Ada Mode
+@cindex Ada, problems
+
+Besides the omissions listed previously (@pxref{Omissions from Ada}),
+we know of several problems with and limitations of Ada mode in
+@value{GDBN},
+some of which will be fixed with planned future releases of the debugger 
+and the GNU Ada compiler.
+
+@itemize @bullet
+@item
+Currently, the debugger 
+has insufficient information to determine whether certain pointers represent
+pointers to objects or the objects themselves.
+Thus, the user may have to tack an extra @code{.all} after an expression
+to get it printed properly.
+
+@item 
+Static constants that the compiler chooses not to materialize as objects in 
+storage are invisible to the debugger.
+
+@item
+Named parameter associations in function argument lists are ignored (the
+argument lists are treated as positional).
+
+@item
+Many useful library packages are currently invisible to the debugger.
+
+@item
+Fixed-point arithmetic, conversions, input, and output is carried out using 
+floating-point arithmetic, and may give results that only approximate those on 
+the host machine.
+
+@item
+The type of the @t{'Address} attribute may not be @code{System.Address}.
+
+@item
+When stopped in a particular subprogram, you can access variables defined
+in other, lexically
+enclosing subprograms by their simple names.  At the moment, however, this
+may not always work; it depends on whether the compiler happens to have
+made the necessary information (the ``static link'') available 
+at execution time, which it can sometimes avoid.  Of course,
+even in those cases where
+the compiler does not provide the information, you can still look at such
+variables by issuing the appropriate number of @code{up} commands to get to
+frame containing the variable you wish to see.   
+Access to non-local variables does not, at the moment, work in
+the test expressions for conditional breakpoints 
+(@pxref{Conditions, ,Break conditions}) unless you happen to specify these 
+while stopped in the subprogram in which they are to be applied.
+
+@item
+Depending on the platform, it is not always possible to set breakpoints
+on nested functions by name (e.g., @code{break foo}).  In effect, the
+nested functions act like local variables of the enclosing function.
+On these platforms, you must wait until @value{GDBN} is stopped in 
+the enclosing function before using this form of @code{break} command.  
+This is not much of a limitation, since you can still set a breakpoint on 
+the first line of the desired function using the usual 
+@code{break @var{file}:@var{line}} syntax.
+
+@item
+The GNAT compiler never generates the prefix @code{Standard} for any of 
+the standard symbols defined by the Ada language.  @value{GDBN} knows about 
+this: it will strip the prefix from names when you use it, and will never
+look for a name you have so qualified among local symbols, nor match against
+symbols in other packages or subprograms.  If you have 
+defined entities anywhere in your program other than parameters and 
+local variables whose simple names match names in @code{Standard}, 
+GNAT's lack of qualification here can cause confusion.  When this happens,
+you can usually resolve the confusion 
+by qualifying the problematic names with package
+@code{Standard} explicitly.  
+@end itemize
+
 @node Unsupported languages
 @section Unsupported languages