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The commands described in this chapter allow you to inquire about the symbols (names of variables, functions and types) defined in your program. This information is inherent in the text of your program and does not change as your program executes. GDB finds it in your program's symbol table, in the file indicated when you started GDB (see section Choosing files), or by one of the file-management commands (see section Commands to specify files).
Occasionally, you may need to refer to symbols that contain unusual characters, which GDB ordinarily treats as word delimiters. The most frequent case is in referring to static variables in other source files (see section Program variables). File names are recorded in object files as debugging symbols, but GDB would ordinarily parse a typical file name, like `foo.c', as the three words `foo' `.' `c'. To allow GDB to recognize `foo.c' as a single symbol, enclose it in single quotes; for example,
p 'foo.c'::x |
looks up the value of x
in the scope of the file `foo.c'.
info address symbol
Describe where the data for symbol is stored. For a register variable, this says which register it is kept in. For a non-register local variable, this prints the stack-frame offset at which the variable is always stored.
Note the contrast with `print &symbol', which does not work at all for a register variable, and for a stack local variable prints the exact address of the current instantiation of the variable.
info symbol addr
Print the name of a symbol which is stored at the address addr. If no symbol is stored exactly at addr, GDB prints the nearest symbol and an offset from it:
(gdb) info symbol 0x54320 _initialize_vx + 396 in section .text |
This is the opposite of the info address
command. You can use
it to find out the name of a variable or a function given its address.
whatis expr
Print the data type of expression expr. expr is not actually evaluated, and any side-effecting operations (such as assignments or function calls) inside it do not take place. See section Expressions.
whatis
Print the data type of $
, the last value in the value history.
ptype typename
Print a description of data type typename. typename may be the name of a type, or for C code it may have the form `class class-name', `struct struct-tag', `union union-tag' or `enum enum-tag'.
ptype expr
ptype
Print a description of the type of expression expr. ptype
differs from whatis
by printing a detailed description, instead
of just the name of the type.
For example, for this variable declaration:
struct complex {double real; double imag;} v; |
the two commands give this output:
(gdb) whatis v type = struct complex (gdb) ptype v type = struct complex { double real; double imag; } |
As with whatis
, using ptype
without an argument refers to
the type of $
, the last value in the value history.
info types regexp
info types
Print a brief description of all types whose names match regexp
(or all types in your program, if you supply no argument). Each
complete typename is matched as though it were a complete line; thus,
`i type value' gives information on all types in your program whose
names include the string value
, but `i type ^value$' gives
information only on types whose complete name is value
.
This command differs from ptype
in two ways: first, like
whatis
, it does not print a detailed description; second, it
lists all source files where a type is defined.
info scope addr
List all the variables local to a particular scope. This command accepts a location--a function name, a source line, or an address preceded by a `*', and prints all the variables local to the scope defined by that location. For example:
(gdb) info scope command_line_handler Scope for command_line_handler: Symbol rl is an argument at stack/frame offset 8, length 4. Symbol linebuffer is in static storage at address 0x150a18, length 4. Symbol linelength is in static storage at address 0x150a1c, length 4. Symbol p is a local variable in register $esi, length 4. Symbol p1 is a local variable in register $ebx, length 4. Symbol nline is a local variable in register $edx, length 4. Symbol repeat is a local variable at frame offset -8, length 4. |
This command is especially useful for determining what data to collect during a trace experiment, see collect.
info source
Show information about the current source file--that is, the source file for the function containing the current point of execution:
info sources
Print the names of all source files in your program for which there is debugging information, organized into two lists: files whose symbols have already been read, and files whose symbols will be read when needed.
info functions
Print the names and data types of all defined functions.
info functions regexp
Print the names and data types of all defined functions
whose names contain a match for regular expression regexp.
Thus, `info fun step' finds all functions whose names
include step
; `info fun ^step' finds those whose names
start with step
. If a function name contains characters
that conflict with the regular expression language (eg.
`operator*()'), they may be quoted with a backslash.
info variables
Print the names and data types of all variables that are declared outside of functions (i.e. excluding local variables).
info variables regexp
Print the names and data types of all variables (except for local variables) whose names contain a match for regular expression regexp.
Some systems allow individual object files that make up your program to be replaced without stopping and restarting your program. For example, in VxWorks you can simply recompile a defective object file and keep on running. If you are running on one of these systems, you can allow GDB to reload the symbols for automatically relinked modules:
set symbol-reloading on
Replace symbol definitions for the corresponding source file when an object file with a particular name is seen again.
set symbol-reloading off
Do not replace symbol definitions when encountering object files of the
same name more than once. This is the default state; if you are not
running on a system that permits automatic relinking of modules, you
should leave symbol-reloading
off, since otherwise GDB
may discard symbols when linking large programs, that may contain
several modules (from different directories or libraries) with the same
name.
show symbol-reloading
Show the current on
or off
setting.
set opaque-type-resolution on
Tell GDB to resolve opaque types. An opaque type is a type
declared as a pointer to a struct
, class
, or
union
--for example, struct MyType *
--that is used in one
source file although the full declaration of struct MyType
is in
another source file. The default is on.
A change in the setting of this subcommand will not take effect until the next time symbols for a file are loaded.
set opaque-type-resolution off
Tell GDB not to resolve opaque types. In this case, the type is printed as follows:
{<no data fields>} |
show opaque-type-resolution
Show whether opaque types are resolved or not.
maint print symbols filename
maint print psymbols filename
maint print msymbols filename
Write a dump of debugging symbol data into the file filename.
These commands are used to debug the GDB symbol-reading code. Only
symbols with debugging data are included. If you use `maint print
symbols', GDB includes all the symbols for which it has already
collected full details: that is, filename reflects symbols for
only those files whose symbols GDB has read. You can use the
command info sources
to find out which files these are. If you
use `maint print psymbols' instead, the dump shows information about
symbols that GDB only knows partially--that is, symbols defined in
files that GDB has skimmed, but not yet read completely. Finally,
`maint print msymbols' dumps just the minimal symbol information
required for each object file from which GDB has read some symbols.
See section Commands to specify files, for a discussion of how
GDB reads symbols (in the description of symbol-file
).
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