User`s guide

Stopping at System Calls

syscall ignore {call | return} {system_call | all}

Clears the breakpoint to stop execution upon entering (call)

or returning from (return) the speciﬁed system call.

If you use the keyword all rather than giving a speciﬁc

system call, dbx clears the breakpoints to stop execution

upon entering (call) or returning from (return) all system

calls.

syscall catch [{call | return}]

Prints a list of all system calls caught upon entry (call) or

return (return). If you provide neither the call nor return

keyword, dbx lists all system calls that are caught.

syscall ignore [{call | return}]

Prints a list of all system calls not caught upon entry (call)

or return (return). If you provide neither the call nor return

keyword, dbx lists all system calls that are ignored.

syscall Prints a summary of the catch and ignore status of all

system calls. The summary is divided into four sections:

1) caught at call, 2) caught at return, 3) ignored at call, and

4) ignored at return.

Note: The fork and sproc system calls are treated specially as they invoke

new processes. The returns from these system calls are controlled by the dbx

variables $promptonfork and$mp_program, not by syscall. This is discussed in

“Handling fork System Calls” on page 104 and “Handling sproc System

Calls and Process Group Debugging” on page 107.The execv and execve

system calls are treated specially as they change a process into a new

program. For more information, see “Handling exec System Calls” on

page 106.

The system calls are listed in /usr/include/sys.s. dbx ignores the case of the

system call names in all syscall commands; therefore, you can use uppercase

or lowercase in these commands.

A particularly useful setting is:

(dbx) syscall catch call exit

This stops your program upon entry to exit. With your program stopped,

you can do a stack trace before the termination to see why exit was called.