@node Parameters
@section Parameters
-@table @strong
-@item Directive:
-@code{.stabs}
-@item Type:
-@code{N_PSYM}
-@item Symbol Descriptor:
-@code{p}
-@end table
+The symbol descriptor @samp{p} is used to refer to parameters which are
+in the arglist. They follow the symbol that represents the procedure
+itself. The value of the symbol is the offset relative to the argument
+list.
-Procedure parameters are represented by the N_PSYM stab type. The
-following source lines show the parameters of the main routine.
+If the parameter is passed in a register, or is allocated as a local
+variable rather than an argument (the latter distinction is important
+for machines in which the argument list offset is relative to something
+different from a local variable offset), then the traditional way to do
+this is to provide two symbols for each argument:
@example
-17 main (argc, argv)
-18 int argc;
-19 char* argv[];
-20 @{
+.stabs "arg:p1" . . .
+.stabs "arg:r1" . . .
@end example
-The N_PSYM stabs describing parameters to a function directly follow
-the N_FUN stab that represents the procedure itself. The N_FUN stab
-immediately follows the code of the procedure it describes. Following
-the N_PSYM parameter stabs are any N_LSYM stabs representing local
-variables.
+Debuggers are expected to use the second one to find the value, and the
+first one to know that it is an argument.
-@example
-@exdent <36> N_FUN - describing the procedure main
+Because this is kind of ugly, some compilers use symbol descriptor @samp{P}
+or @samp{R} to indicate an argument which is in a register. The symbol
+value is the register number. @samp{P} and @samp{R} mean the same
+thing, the difference is that @samp{P} is a GNU invention and @samp{R}
+is an IBM (xcoff) invention. As of version 4.9, GDB should handle
+either one.
-94 .stabs "main:F1",36,0,0,_main
+There is no symbol descriptor analogous to @samp{P} for local variables.
+Some compilers are said to use the pair of symbols approach described
+above, but I don't know which ones. On the intel 960, the type of the
+variable indicates whether a @samp{p} symbol's value is an the argument
+list offset or a local variable offset.
-@exdent <160> N_PSYM - parameters
-@exdent .stabs "name:sym_desc(value_param)type_ref(int)", N_PSYM,
-@exdent NIL, NIL, frame_ptr_offset
+As a simple example, the code
-95 .stabs "argc:p1",160,0,0,68
-
-@exdent <160> N_PSYM - parameter
-@exdent .stabs "name:sym_desc(value_param)type_def(20)=ptr_to type_def(21)=
-@exdent ptr_to type_ref(char)
+@example
+17 main (argc, argv)
+18 int argc;
+19 char **argv;
+20 @{
+@end example
+
+produces the stabs
+@example
+94 .stabs "main:F1",36,0,0,_main ; 36 is N_FUN
+95 .stabs "argc:p1",160,0,0,68 ; 160 is N_PSYM
96 .stabs "argv:p20=*21=*2",160,0,0,72
@end example
-The type definition of argv is interesting because it defines two new
-types in terms of an existing one. The ``array'' argv is really a
-pointer, according to C language rules, since it is declared as a
-parameter. Its element type is character pointers. Thus the type of
-argv is ptr to ptr to char. The stab for argv contains nested
-type_definitions. Type 21 is ptr to type 2 (char) and argv (type 20)
-is ptr to type 21.
+The type definition of argv is interesting because it contains several
+type definitions. Type 21 is ptr to type 2 (char) and argv (type 20) is
+ptr to type 21.
@node Aggregate Types
@chapter Aggregate Types
@node Symbol descriptors
@section Table C: Symbol descriptors
-@example
-descriptor meaning
--------------------------------------------------
-(empty) local variable
- f local function
- F global function
- G global variable
- p value parameter
- r register variable
- S static global variable
- t type name
- T enumeration, struct or type tag
- V static local variable
-@end example
+@table @code
+@item (empty)
+Local variable, @xref{Automatic variables}.
+
+@item f
+Local function, @xref{Procedures}.
+
+@item F
+Global function, @xref{Procedures}.
+
+@item t
+Type name, @xref{Typedefs}.
+
+@item T
+enumeration, struct or union tag, @xref{Unions}.
+
+@item G
+Global variable, @xref{Global Variables}.
+
+@item r
+Register variable, @xref{Register variables}.
+
+@item S
+Static file scope variable @xref{Initialized statics},
+@xref{Un-initialized static variables}.
+
+@item V
+Static procedure scope variable @xref{Initialized statics},
+@xref{Un-initialized static variables}.
+
+@item p
+Argument list parameter @xref{Parameters}.
+
+@item P
+@item R
+Register parameter @xref{Parameters}.
+@end table
@node Type Descriptors
@section Table D: Type Descriptors
@node xcoff-differences
@appendix Differences between GNU stabs in a.out and GNU stabs in xcoff
-(The AIX/RS6000 native object file format is xcoff with stabs)
+@c FIXME: Merge *all* these into the main body of the document.
+(The AIX/RS6000 native object file format is xcoff with stabs). This
+appendix only covers those differences which are not covered in the main
+body of this document.
@itemize @bullet
@item
@item
If the xcoff stab is a N_FUN (C_FUN) then follow the string field with
,. instead of just ,
-
-@item
-The symbol descriptor for register parameters is P for a.out and R for
-xcoff.
@end itemize
@node Sun-differences
@appendix Differences between GNU stabs and Sun native stabs.
+@c FIXME: Merge all this stuff into the main body of the document.
+
@itemize @bullet
@item
GNU C stabs define *all* types, file or procedure scope, as
@item
Stabs describing block scopes, N_LBRAC and N_RBRAC are supposed to
contain the nesting level of the block in the desc field, re Sun doc.
-GNU stabs always have 0 in that field.
+GNU stabs always have 0 in that field. dbx seems not to care.
@item
Sun C stabs use type number pairs in the format (a,b) where a is a
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