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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

Capabilities of Runtime Checking

When to Use Runtime Checking

Runtime Checking Requirements

Using Runtime Checking

Turning On Memory Use and Memory Leak Checking

Turning On Memory Access Checking

Turning On All Runtime Checking

Turning Off Runtime Checking

Running Your Program

Using Access Checking

Understanding the Memory Access Error Report

Memory Access Errors

Using Memory Leak Checking

Detecting Memory Leak Errors

Possible Leaks

Checking for Leaks

Understanding the Memory Leak Report

Generating a Leak Report

Combining Leaks

Fixing Memory Leaks

Using Memory Use Checking

Suppressing Errors

Types of Suppression

Suppression by Scope and Type

Suppression of Last Error

Limiting the Number of Errors Reported

Suppressing Error Examples

Default Suppressions

Using Suppression to Manage Errors

Using Runtime Checking on a Child Process

Using Runtime Checking on an Attached Process

On a System Running Solaris

On a System Running Linux

Using Fix and Continue With Runtime Checking

Runtime Checking Application Programming Interface

Using Runtime Checking in Batch Mode

bcheck Syntax

bcheck Examples

Enabling Batch Mode Directly From dbx

Troubleshooting Tips

Runtime Checking Limitations

Works Better With More Symbols and Debug Information

SIGSEGV and SIGALTSTACK Signals Are Restricted on x86 Platforms

Works Better When Sufficient Patch Area is Available Within 8 MB of All Existing Code (SPARC platforms only).

Runtime Checking Errors

Access Errors

Bad Free (baf) Error

Duplicate Free (duf) Error

Misaligned Free (maf) Error

Misaligned Read (mar) Error

Misaligned Write (maw) Error

Out of Memory (oom) Error

Read From Array Out-of-Bounds (rob) Error

Read From Unallocated Memory (rua) Error

Read From Uninitialized Memory (rui) Error

Write to Array Out-of-Bounds Memory (wob) Error

Write to Read-Only Memory (wro) Error

Write to Unallocated Memory (wua) Error

Memory Leak Errors

Address in Block (aib) Error

Address in Register (air) Error

Memory Leak (mel) Error

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

19.  Using dbx With the Korn Shell

20.  Debugging Shared Libraries

A.  Modifying a Program State

B.  Event Management

C.  Macros

D.  Command Reference


Using Runtime Checking

To use runtime checking, enable the type of checking you want to use before you run the program.

Turning On Memory Use and Memory Leak Checking

To turn on memory use and memory leak checking, type:

(dbx) check -memuse

When memory use checking or memory leak checking is turned on, the showblock command shows the details about the heap block at a given address. The details include the location of the block’s allocation and its size. For more information, see showblock Command.

Turning On Memory Access Checking

To turn on memory access checking only, type:

(dbx) check -access

Turning On All Runtime Checking

To turn on memory leak, memory use, and memory access checking, type:

(dbx) check -all

For more information, see check Command.

Turning Off Runtime Checking

To turn off runtime checking entirely, type:

(dbx) uncheck -all

For detailed information, see uncheck Command.

Running Your Program

After turning on the types of runtime checking you want, run the program being tested, with or without breakpoints.

The program runs normally, but slowly because each memory access is checked for validity just before it occurs. If dbx detects invalid access, it displays the type and location of the error. Control returns to you (unless the dbx environment variable rtc_auto_continue is set to on (see Setting dbx Environment Variables.)

You can then issue dbx commands, such as where to get the current stack trace or print to examine variables. If the error is not a fatal error, you can continue execution of the program with the cont command. The program continues to the next error or breakpoint, whichever is detected first. For detailed information, see cont Command.

If the rtc_auto_continue environment variable is set to on, runtime checking continues to find errors, and keeps running automatically. It redirects errors to the file named by the dbx environment variable rtc_error_log_file_name. (See Setting dbx Environment Variables.) The default log file name is /tmp/dbx.errlog.uniqueid.

You can limit the reporting of runtime checking errors using the suppress command. For detailed information, see suppress Command.

Below is a simple example showing how to turn on memory access and memory use checking for a program called hello.c.

% cat -n hello.c
     1 #include <stdio.h>
     2 #include <stdlib.h>
     3 #include <string.h>
     5 char *hello1, *hello2;
     7 void
     8 memory_use()
     9 {
    10      hello1 = (char *)malloc(32);
    11      strcpy(hello1, "hello world");
    12      hello2 = (char *)malloc(strlen(hello1)+1);
    13      strcpy(hello2, hello1);
    14 }
    16 void
    17 memory_leak()
    18 {
    19      char *local;
    20      local = (char *)malloc(32);
    21      strcpy(local, "hello world");
    22 }
    24 void
    25 access_error()
    26 {
    27      int i,j;
    29      i = j;
    30 }
    32 int
    33 main()
    34 {
    35      memory_use();
    36      access_error();
    37      memory_leak();
    38      printf("%s\n", hello2);
    39      return 0;
    40 }
% cc -g -o hello hello.c

% dbx -C hello

(dbx) check -access
access checking - ON
(dbx) check -memuse
memuse checking - ON
(dbx) run Running: hello
(process id 18306)
Enabling Error Checking... done
Read from uninitialized (rui):
Attempting to read 4 bytes at address 0xeffff068
     which is 96 bytes above the current stack pointer
Variable is ’j’
Current function is access_error
    29       i = j;
(dbx) cont
hello world
Checking for memory leaks...
Actual leaks report    (actual leaks:         1 total size:      32 bytes)

 Total      Num of  Leaked     Allocation call stack
 Size       Blocks  Block
==========  ====== ==========  =======================================
        32       1    0x21aa8  memory_leak < main

Possible leaks report  (possible leaks:       0  total size:      0 bytes)

Checking for memory use...
Blocks in use report   (blocks in use:        2  total size:      44 bytes

 Total     % of Num of  Avg    Allocation call stack
 Size      All  Blocks  Size
========== ==== ====== ======  =======================================
        32  72%      1     32  memory_use < main
        12  27%      1     12  memory_use < main

execution completed, exit code is 0

The function access_error() reads variable j before it is initialized. Runtime checking reports this access error as a Read from uninitialized (rui).

The function memory_leak() does not free the variable local before it returns. When memory_leak() returns, this variable goes out of scope and the block allocated at line 20 becomes a leak.

The program uses global variables hello1 and hello2, which are in scope all the time. They both point to dynamically allocated memory, which is reported as Blocks in use (biu).