Greetings, I have been working on a few experimental system calls using a ptrace mechanism similar to UML to implement the calls. Naturally this lead me to look at PTRACE_SYSEMU vs. PTRACE_SYSCALL. Since the extra system calls are implemented entirely by the ptrace thread it seems a shame to take the context switch on entry and exit from the call. In some cases, I need to also implement a few of the standard Linux kernel calls in the ptrace thread as well, based on parameters of the call (for example, writes to specific open files).
The patch below for x86_64 implements a scheme where a ptraced system call is skipped if the ptrace thread sets a return value (in RAX) when it handles the syscall entry. Otherwise things proceed normally. A similar change is even easier on i386 since the needed logic is already in entry.S for SYSEMU. I chose changing RAX as the trigger since that is otherwise a useless thing for a tracing thread to do at syscall entry. G'day, sjames ||||| |||| ||||||||||||| ||| by Linux Labs International, Inc. Steven James, CTO 55 Marietta Street Suite 1830 Atlanta, Ga 30303 866 824 9737 support ------------------------------------------------------- Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642 _______________________________________________ User-mode-linux-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel
