(gdb.info) Memory

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 Examining memory
 ================
 
    You can use the command `x' (for "examine") to examine memory in any
 of several formats, independently of your program's data types.
 
 `x/NFU ADDR'
 `x ADDR'
 `x'
      Use the `x' command to examine memory.
 
    N, F, and U are all optional parameters that specify how much memory
 to display and how to format it; ADDR is an expression giving the
 address where you want to start displaying memory.  If you use defaults
 for NFU, you need not type the slash `/'.  Several commands set
 convenient defaults for ADDR.
 
 N, the repeat count
      The repeat count is a decimal integer; the default is 1.  It
      specifies how much memory (counting by units U) to display.
 
 F, the display format
      The display format is one of the formats used by `print', `s'
      (null-terminated string), or `i' (machine instruction).  The
      default is `x' (hexadecimal) initially.  The default changes each
      time you use either `x' or `print'.
 
 U, the unit size
      The unit size is any of
 
     `b'
           Bytes.
 
     `h'
           Halfwords (two bytes).
 
     `w'
           Words (four bytes).  This is the initial default.
 
     `g'
           Giant words (eight bytes).
 
      Each time you specify a unit size with `x', that size becomes the
      default unit the next time you use `x'.  (For the `s' and `i'
      formats, the unit size is ignored and is normally not written.)
 
 ADDR, starting display address
      ADDR is the address where you want GDB to begin displaying memory.
      The expression need not have a pointer value (though it may); it
      is always interpreted as an integer address of a byte of memory.
       Expressions Expressions, for more information on
      expressions.  The default for ADDR is usually just after the last
      address examined--but several other commands also set the default
      address: `info breakpoints' (to the address of the last breakpoint
      listed), `info line' (to the starting address of a line), and
      `print' (if you use it to display a value from memory).
 
    For example, `x/3uh 0x54320' is a request to display three halfwords
 (`h') of memory, formatted as unsigned decimal integers (`u'), starting
 at address `0x54320'.  `x/4xw $sp' prints the four words (`w') of
 memory above the stack pointer (here, `$sp';  Registers
 Registers.) in hexadecimal (`x').
 
    Since the letters indicating unit sizes are all distinct from the
 letters specifying output formats, you do not have to remember whether
 unit size or format comes first; either order works.  The output
 specifications `4xw' and `4wx' mean exactly the same thing.  (However,
 the count N must come first; `wx4' does not work.)
 
    Even though the unit size U is ignored for the formats `s' and `i',
 you might still want to use a count N; for example, `3i' specifies that
 you want to see three machine instructions, including any operands.
 The command `disassemble' gives an alternative way of inspecting
 machine instructions; see  Source and machine code Machine Code.
 
    All the defaults for the arguments to `x' are designed to make it
 easy to continue scanning memory with minimal specifications each time
 you use `x'.  For example, after you have inspected three machine
 instructions with `x/3i ADDR', you can inspect the next seven with just
 `x/7'.  If you use <RET> to repeat the `x' command, the repeat count N
 is used again; the other arguments default as for successive uses of
 `x'.
 
    The addresses and contents printed by the `x' command are not saved
 in the value history because there is often too much of them and they
 would get in the way.  Instead, GDB makes these values available for
 subsequent use in expressions as values of the convenience variables
 `$_' and `$__'.  After an `x' command, the last address examined is
 available for use in expressions in the convenience variable `$_'.  The
 contents of that address, as examined, are available in the convenience
 variable `$__'.
 
    If the `x' command has a repeat count, the address and contents saved
 are from the last memory unit printed; this is not the same as the last
 address printed if several units were printed on the last line of
 output.
 

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