dbx supports Runtime Checking of a child process if RTC is enabled for the parent and the dbxenv variable follow_fork_mode is set to child. When a fork happens, dbx automatically performs RTC on the child. If the program does an exec(), the RTC settings of the program calling exec() are passed on to the program.
At any given time, just one process can be under RTC control. Following is an example:
% cat -n program1.c 1 #include <sys/types.h> 2 #include <unistd.h> 3 #include <stdio.h> 4 5 int 6 main() 7 { 8 pid_t child_pid; 9 int parent_i, parent_j; 10 11 parent_i = parent_j; 12 13 child_pid = fork(); 14 15 if (child_pid == -1) { 16 printf("parent: Fork failed\n"); 17 return 1; 18 } else if (child_pid == 0) { 19 int child_i, child_j; 20 21 printf("child: In child\n"); 22 child_i = child_j; 23 if (execl("./program2", NULL) == -1) { 24 printf("child: exec of program2 failed\n"); 25 exit(1); 26 } 27 } else { 28 printf("parent: child's pid = %d\n", child_pid); 29 } 30 return 0; 31 } %
% cat -n program2.c 1 2 #include <stdio.h> 3 4 main() 5 { 6 int program2_i, program2_j; 7 8 printf ("program2: pid = %d\n", getpid()); 9 program2_i = program2_j; 10 11 malloc(8); 12 13 return 0; 14 } %
RTC reports first error in the parent, program1 % cc -g -o program1 program1.c % cc -g -o program2 program2.c % dbx -C program1 Reading symbolic information for program1 Reading symbolic information for rtld /usr/lib/ld.so.1 Reading symbolic information for librtc.so Reading symbolic information for libc.so.1 Reading symbolic information for libdl.so.1 Reading symbolic information for libc_psr.so.1 (dbx) check -all access checking - ON memuse checking - ON (dbx) dbxenv follow_fork_mode child (dbx) run Running: program1 (process id 3885) Enabling Error Checking... done Read from uninitialized (rui): Attempting to read 4 bytes at address 0xeffff110 which is 104 bytes above the current stack pointer Variable is 'parent_j' Current function is main 11 parent_i = parent_j;
Because follow_fork_mode is set to child, when the fork occurs error checking is switched from the parent to the child process RTC reports an error in the child When the exec of program2 occurs, the RTC settings are inherited by program2 so access and memory use checking are enabled for that process RTC reports an access error in the executed program, program2 (dbx) cont dbx: warning: Fork occurred; error checking disabled in parent detaching from process 3885 Attached to process 3886 stopped in _fork at 0xef6b6040 0xef6b6040: _fork+0x0008: bgeu _fork+0x30 Current function is main 13 child_pid = fork(); parent: child's pid = 3886 (dbx) cont child: In child Read from uninitialized (rui): Attempting to read 4 bytes at address 0xeffff108 which is 96 bytes above the current stack pointer Variable is 'child_j' Current function is main 22 child_i = child_j; (dbx) cont dbx: process 3886 about to exec("./program2") dbx: program "./program2" just exec'ed dbx: to go back to the original program use "debug $oprog" Reading symbolic information for program2 Skipping ld.so.1, already read Skipping librtc.so, already read Skipping libc.so.1, already read Skipping libdl.so.1, already read Skipping libc_psr.so.1, already read Enabling Error Checking... done stopped in main at line 8 in file "program2.c" 8 printf ("program2: pid = %d\n", getpid()); (dbx) cont program2: pid = 3886 Read from uninitialized (rui): Attempting to read 4 bytes at address 0xeffff13c which is 100 bytes above the current stack pointer Variable is 'program2_j' Current function is main 9 program2_i = program2_j; (dbx) cont Checking for memory leaks...
RTC prints a memory use and memory leak report for the process that exited while under RTC control, program2 Actual leaks report (actual leaks: 1 total size: 8 bytes) Total Num of Leaked Allocation call stack Size Blocks Block Address ====== ====== ========== ==================================== 8 1 0x20c50 main Possible leaks report (possible leaks: 0 total size: 0 bytes) execution completed, exit code is 0