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Oracle Solaris Studio 12.3: Debugging a Program With dbx     Oracle Solaris Studio 12.3 Information Library
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Document Information


1.  Getting Started With dbx

2.  Starting dbx

3.  Customizing dbx

4.  Viewing and Navigating To Code

5.  Controlling Program Execution

6.  Setting Breakpoints and Traces

7.  Using the Call Stack

8.  Evaluating and Displaying Data

9.  Using Runtime Checking

10.  Fixing and Continuing

11.  Debugging Multithreaded Applications

12.  Debugging Child Processes

13.  Debugging OpenMP Programs

14.  Working With Signals

15.  Debugging C++ With dbx

16.  Debugging Fortran Using dbx

17.  Debugging a Java Application With dbx

18.  Debugging at the Machine-Instruction Level

Examining the Contents of Memory

Using the examine or x Command

Using Addresses

Using Formats

Using Count

Examples of Using an Address

Using the dis Command

Using the listi Command

Stepping and Tracing at Machine-Instruction Level

Single Stepping at the Machine-Instruction Level

Tracing at the Machine-Instruction Level

Setting Breakpoints at the Machine-Instruction Level

Setting a Breakpoint at an Address

Using the regs Command

Platform-Specific Registers

SPARC Register Information

x86 Register Information

AMD64 Register Information

19.  Using dbx With the Korn Shell

20.  Debugging Shared Libraries

A.  Modifying a Program State

B.  Event Management

C.  Macros

D.  Command Reference


Examining the Contents of Memory

Using addresses and the examine or x command, you can examine the content of memory locations as well as print the assembly language instruction at each address. Using a command derived from adb(1), the assembly language debugger, you can query for:

You can print the assembly commands using the dis command and the listi command. (See Using the dis Command and Using the listi Command.)

Using the examine or x Command

Use the examine command, or its alias x, to display memory contents or addresses.

Use the following syntax to display the contents of memory starting at address for count items in format format. The default address is the next one after the last address previously displayed. The default count is 1. The default format is the same as was used in the previous examine command, or X if this is the first command given.

The syntax for the examine command is:

examine [address] [/ [count] [format]]

To display the contents of memory from address1 through address2 inclusive, in format format, type:

examine address1, address2 [/ [format]]

Display the address, instead of the contents of the address in the given format by typing:

examine address = [format]

To print the value stored at the next address after the one last displayed by examine, type:

examine +/ i

To print the value of an expression, enter the expression as an address:

examine address=format
examine address=

Using Addresses

The address is any expression resulting in or usable as an address. The address may be replaced with a + (plus sign), which displays the contents of the next address in the default format.

For example, the following are valid addresses:

An absolute address
Address of a function
Offset from a function address
Address of a variable
A pointer-value variable pointing to a string

Symbolic addresses used to display memory are specified by preceding a name with an ampersand (&). Function names can be used without the ampersand; &main is equal to main. Registers are denoted by preceding a name with a dollar sign ($).

Using Formats

The format is the address display format in which dbx displays the results of a query. The output produced depends on the current display format. To change the display format, supply a different format code.

The default format set at the start of each dbx session is X, which displays an address or value as a 32-bit word in hexadecimal. The following memory display formats are legal.

Display as an assembly instruction.
Display as 16 bits (2 bytes) in decimal.
Display as 32 bits (4 bytes) in decimal.
Display as 16 bits (2 bytes) in octal.
Display as 32 bits (4 bytes) in octal.
Display as 16 bits (2 bytes) in hexadecimal.
Display as 32 bits (4 bytes) in hexadecimal. (default format)
Display as a byte in octal.
Display as a character.
Display as a wide character.
Display as a string of characters terminated by a null byte.
Display as a wide character string.
Display as a single-precision floating point number.
F, g
Display as a double-precision floating point number.
Display as an extended-precision floating point number.
ld, lD
Display 32 bits (4 bytes) in decimal (same as D).
lo, lO
Display 32 bits (4 bytes) in octal (same as O).
lx, LX
Display 32 bits (4 bytes) in hexadecimal (same as X).
Ld, LD
Display 64 bits (8 bytes) in decimal.
Lo, LO
Display 64 bits (8 bytes) in octal.
Lx, LX
Display 64 bits (8 bytes) in hexadecimal.

Using Count

The count is a repetition count in decimal. The increment size depends on the memory display format.

Examples of Using an Address

The following examples show how to use an address with count and format options to display five successive disassembled instructions starting from the current stopping point.

For SPARC based systems:

(dbx) stepi
stopped in main at 0x108bc
0x000108bc: main+0x000c: st    %l0, [%fp - 0x14]
(dbx) x 0x108bc/5i
0x000108bc: main+0x000c: st    %l0, [%fp - 0x14]
0x000108c0: main+0x0010: mov   0x1,%l0
0x000108c4: main+0x0014: or    %l0,%g0, %o0
0x000108c8: main+0x0018: call  0x00020b90 [unresolved PLT 8: malloc]
0x000108cc: main+0x001c: nop

For x86 based systems:

(dbx) x &main/5i
0x08048988: main       :  pushl  %ebp
0x08048989: main+0x0001:  movl   %esp,%ebp
0x0804898b: main+0x0003:  subl   $0x28,%esp
0x0804898e: main+0x0006:  movl   0x8048ac0,%eax
0x08048993: main+0x000b:  movl   %eax,-8(%ebp)

Using the dis Command

The dis command is equivalent to the examine command with i as the default display format.

Here is the syntax for the dis command.

dis [address] [address1, address2] [/count]

The dis command:

Using the listi Command

To display source lines with their corresponding assembly instructions, use the listi command, which is equivalent to the command list -i. See the discussion of list -i in Printing a Source Listing.

For SPARC based systems:

(dbx) listi 13, 14
   13       i = atoi(argv[1]);
0x0001083c: main+0x0014:  ld      [%fp + 0x48], %l0
0x00010840: main+0x0018:  add     %l0, 0x4, %l0
0x00010844: main+0x001c:  ld      [%l0], %l0
0x00010848: main+0x0020:  or      %l0, %g0, %o0
0x0001084c: main+0x0024:  call    0x000209e8 [unresolved PLT 7: atoi]
0x00010850: main+0x0028:  nop
0x00010854: main+0x002c:  or      %o0, %g0, %l0
0x00010858: main+0x0030:  st      %l0, [%fp - 0x8]
   14       j = foo(i);
0x0001085c: main+0x0034:  ld      [%fp - 0x8], %l0
0x00010860: main+0x0038:  or      %l0, %g0, %o0
0x00010864: main+0x003c:  call    foo
0x00010868: main+0x0040:  nop
0x0001086c: main+0x0044:  or      %o0, %g0, %l0
0x00010870: main+0x0048:  st      %l0, [%fp - 0xc]

For x86 based systems:

(dbx) listi 13, 14
   13       i = atoi(argv[1]);
0x080488fd: main+0x000d:  movl   12(%ebp),%eax
0x08048900: main+0x0010:  movl   4(%eax),%eax
0x08048903: main+0x0013:  pushl  %eax
0x08048904: main+0x0014:  call   atoi <0x8048798>
0x08048909: main+0x0019:  addl   $4,%esp
0x0804890c: main+0x001c:  movl   %eax,-8(%ebp)
   14       j = foo(i);
0x0804890f: main+0x001f:  movl   -8(%ebp),%eax
0x08048912: main+0x0022:  pushl  %eax
0x08048913: main+0x0023:  call   foo <0x80488c0>
0x08048918: main+0x0028:  addl   $4,%esp
0x0804891b: main+0x002b:  movl   %eax,-12(%ebp)