Re: Q: what user_enable_single_step() actually means?

[Oleg Nesterov]

On 09/21, Oleg Nesterov wrote:
>
> Yes, I modified the patch a bit (see below) to print the syscall number,

Forgot to attach the patch. I guess it is not really needed, but
just in case.

Oleg.

--- TTT/kernel/sys.c~TF_FBG     2009-06-17 14:11:26.000000000 +0200
+++ TTT/kernel/sys.c    2009-09-21 20:03:27.000000000 +0200
@@ -1428,6 +1428,12 @@ SYSCALL_DEFINE5(prctl, int, option, unsi
 
        error = 0;
        switch (option) {
+               case 666:
+                       printk(KERN_INFO "prctl: before=%lX\n", 
task_pt_regs(current)->flags);
+                       user_enable_single_step(current);
+                       printk(KERN_INFO "prctl: after=%lX\n", 
task_pt_regs(current)->flags);
+                       break;
+
                case PR_SET_PDEATHSIG:
                        if (!valid_signal(arg2)) {
                                error = -EINVAL;
--- TTT/arch/x86/kernel/ptrace.c~TF_FBG 2009-06-11 14:16:46.000000000 +0200
+++ TTT/arch/x86/kernel/ptrace.c        2009-09-21 21:18:00.000000000 +0200
@@ -1446,6 +1446,8 @@ void send_sigtrap(struct task_struct *ts
 {
        struct siginfo info;
 
+       printk(KERN_INFO "send_sigtrap: ip=%lX\n", regs->ip);
+
        tsk->thread.trap_no = 1;
        tsk->thread.error_code = error_code;
 
@@ -1520,6 +1522,8 @@ asmregparm long syscall_trace_enter(stru
 
 asmregparm void syscall_trace_leave(struct pt_regs *regs)
 {
+       printk(KERN_INFO "trace_leave enter: ip=%lX nr=%ld\n", regs->ip, 
regs->orig_ax);
+
        if (unlikely(current->audit_context))
                audit_syscall_exit(AUDITSC_RESULT(regs->ax), regs->ax);
 
@@ -1543,6 +1547,8 @@ asmregparm void syscall_trace_leave(stru
         * system call instruction.
         */
        if (test_thread_flag(TIF_SINGLESTEP) &&
-           tracehook_consider_fatal_signal(current, SIGTRAP))
+           tracehook_consider_fatal_signal(current, SIGTRAP)) {
+               printk(KERN_INFO "trace_leave sends SIGTRAP\n");
                send_sigtrap(current, regs, 0, TRAP_BRKPT);
+       }
 }