23.4.3.17 Guile representation of Symbols.

GDB represents every variable, function and type as an entry in a symbol table. See Examining the Symbol Table. Guile represents these symbols in GDB with the <gdb:symbol> object.

The following symbol-related procedures are provided by the (gdb) module:

Scheme Procedure: symbol? object

Return #t if object is an object of type <gdb:symbol>. Otherwise return #f.

Scheme Procedure: symbol-valid? symbol

Return #t if the <gdb:symbol> object is valid, #f if not. A <gdb:symbol> object can become invalid if the symbol it refers to does not exist in GDB any longer. All other <gdb:symbol> procedures will throw an exception if it is invalid at the time the procedure is called.

Scheme Procedure: symbol-type symbol

Return the type of symbol or #f if no type is recorded. The result is an object of type <gdb:type>. See Types In Guile.

Scheme Procedure: symbol-symtab symbol

Return the symbol table in which symbol appears. The result is an object of type <gdb:symtab>. See Symbol Tables In Guile.

Scheme Procedure: symbol-line symbol

Return the line number in the source code at which symbol was defined. This is an integer.

Scheme Procedure: symbol-name symbol

Return the name of symbol as a string.

Scheme Procedure: symbol-linkage-name symbol

Return the name of symbol, as used by the linker (i.e., may be mangled).

Scheme Procedure: symbol-print-name symbol

Return the name of symbol in a form suitable for output. This is either name or linkage_name, depending on whether the user asked GDB to display demangled or mangled names.

Scheme Procedure: symbol-addr-class symbol

Return the address class of the symbol. This classifies how to find the value of a symbol. Each address class is a constant defined in the (gdb) module and described later in this chapter.

Scheme Procedure: symbol-needs-frame? symbol

Return #t if evaluating symbol’s value requires a frame (see Frames In Guile) and #f otherwise. Typically, local variables will require a frame, but other symbols will not.

Scheme Procedure: symbol-argument? symbol

Return #t if symbol is an argument of a function. Otherwise return #f.

Scheme Procedure: symbol-constant? symbol

Return #t if symbol is a constant. Otherwise return #f.

Scheme Procedure: symbol-function? symbol

Return #t if symbol is a function or a method. Otherwise return #f.

Scheme Procedure: symbol-variable? symbol

Return #t if symbol is a variable. Otherwise return #f.

Scheme Procedure: symbol-value symbol [#:frame frame]

Compute the value of symbol, as a <gdb:value>. For functions, this computes the address of the function, cast to the appropriate type. If the symbol requires a frame in order to compute its value, then frame must be given. If frame is not given, or if frame is invalid, then an exception is thrown.

Scheme Procedure: lookup-symbol name [#:block block] [#:domain domain]

This function searches for a symbol by name. The search scope can be restricted to the parameters defined in the optional domain and block arguments.

name is the name of the symbol. It must be a string. The optional block argument restricts the search to symbols visible in that block. The block argument must be a <gdb:block> object. If omitted, the block for the current frame is used. The optional domain argument restricts the search to the domain type. The domain argument must be a domain constant defined in the (gdb) module and described later in this chapter.

The result is a list of two elements. The first element is a <gdb:symbol> object or #f if the symbol is not found. If the symbol is found, the second element is #t if the symbol is a field of a method’s object (e.g., this in C++), otherwise it is #f. If the symbol is not found, the second element is #f.

Scheme Procedure: lookup-global-symbol name [#:domain domain]

This function searches for a global symbol by name. The search scope can be restricted by the domain argument.

name is the name of the symbol. It must be a string. The optional domain argument restricts the search to the domain type. The domain argument must be a domain constant defined in the (gdb) module and described later in this chapter.

The result is a <gdb:symbol> object or #f if the symbol is not found.

The available domain categories in <gdb:symbol> are represented as constants in the (gdb) module:

SYMBOL_UNDEF_DOMAIN

This is used when a domain has not been discovered or none of the following domains apply. This usually indicates an error either in the symbol information or in GDB’s handling of symbols.

SYMBOL_VAR_DOMAIN

This domain contains variables, function names, typedef names and enum type values.

SYMBOL_FUNCTION_DOMAIN

This domain contains functions.

SYMBOL_TYPE_DOMAIN

This domain contains types. In a C-like language, types using a tag (the name appearing after a struct, union, or enum keyword) will not appear here; in other languages, all types are in this domain.

SYMBOL_STRUCT_DOMAIN

This domain holds struct, union and enum tag names. This domain is only used for C-like languages. For example, in this code:

struct type_one { int x; };
typedef struct type_one type_two;

Here type_one will be in SYMBOL_STRUCT_DOMAIN, but type_two will be in SYMBOL_TYPE_DOMAIN.

SYMBOL_LABEL_DOMAIN

This domain contains names of labels (for gotos).

SYMBOL_VARIABLES_DOMAIN

This domain holds a subset of the SYMBOLS_VAR_DOMAIN; it contains everything minus functions and types.

SYMBOL_FUNCTIONS_DOMAIN

This domain contains all functions.

SYMBOL_TYPES_DOMAIN

This domain contains all types.

The available address class categories in <gdb:symbol> are represented as constants in the gdb module:

When searching for a symbol, the desired domain constant can be passed verbatim to the lookup function.

For more complex searches, there is a corresponding set of constants, each named after one of the preceding constants, but with the ‘SEARCH’ prefix replacing the ‘SYMBOL’ prefix; for example, SEARCH_LABEL_DOMAIN. These may be or’d together to form a search constant.

SYMBOL_LOC_UNDEF

If this is returned by address class, it indicates an error either in the symbol information or in GDB’s handling of symbols.

SYMBOL_LOC_CONST

Value is constant int.

SYMBOL_LOC_STATIC

Value is at a fixed address.

SYMBOL_LOC_REGISTER

Value is in a register.

SYMBOL_LOC_ARG

Value is an argument. This value is at the offset stored within the symbol inside the frame’s argument list.

SYMBOL_LOC_REF_ARG

Value address is stored in the frame’s argument list. Just like LOC_ARG except that the value’s address is stored at the offset, not the value itself.

SYMBOL_LOC_REGPARM_ADDR

Value is a specified register. Just like LOC_REGISTER except the register holds the address of the argument instead of the argument itself.

SYMBOL_LOC_LOCAL

Value is a local variable.

SYMBOL_LOC_TYPEDEF

Value not used. Symbols in the domain SYMBOL_STRUCT_DOMAIN all have this class.

SYMBOL_LOC_BLOCK

Value is a block.

SYMBOL_LOC_CONST_BYTES

Value is a byte-sequence.

SYMBOL_LOC_UNRESOLVED

Value is at a fixed address, but the address of the variable has to be determined from the minimal symbol table whenever the variable is referenced.

SYMBOL_LOC_OPTIMIZED_OUT

The value does not actually exist in the program.

SYMBOL_LOC_COMPUTED

The value’s address is a computed location.