@section Parameters
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.
-
-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
+in the arglist. Symbols have symbol type @samp{N_PSYM}. The value of
+the symbol is the offset relative to the argument list.
+
+If the parameter is passed in a register, then the traditional way to do
this is to provide two symbols for each argument:
@example
-.stabs "arg:p1" . . .
-.stabs "arg:r1" . . .
+.stabs "arg:p1" . . . ; N_PSYM
+.stabs "arg:r1" . . . ; N_RSYM
@end example
Debuggers are expected to use the second one to find the value, and the
first one to know that it is an argument.
-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.
-
-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.
+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. Symbol type @samp{C_RPSYM} is used with @samp{R} and
+@samp{N_RSYM} is used with @samp{P}.
+
+There is another case similar to an argument in a register, which is an
+argument which is actually stored as a local variable. The only case I
+know of where this happens is when the argument was passed in a register
+and then the compiler stores it as a local variable. In this case the
+compiler would probably be much better off claiming that it's in a
+register, but at least in one case this isn't done. Some compilers are
+said to use the pair of symbols approach described above ("arg:p"
+followed by "arg:"), but I don't which if any. GCC, at least on the
+960, uses a @samp{p} symbol descriptor for this case but uses
+@samp{N_LSYM} instead of @samp{N_PSYM} to distinguish it. In this case
+the value of the symbol is an offset relative to the local variables for
+that function, not relative to the arguments.
As a simple example, the code
@example
-17 main (argc, argv)
-18 int argc;
-19 char **argv;
-20 @{
+main (argc, argv)
+ int argc;
+ char **argv;
+@{
@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
+.stabs "main:F1",36,0,0,_main ; 36 is N_FUN
+.stabs "argc:p1",160,0,0,68 ; 160 is N_PSYM
+.stabs "argv:p20=*21=*2",160,0,0,72
@end example
The type definition of argv is interesting because it contains several
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