Re: [uml-devel] Kernel panic: check_ptrace : child exited with status 0x100

[Bodo Stroesser <bstroesser@fujitsu-siemens.com>]

Bodo Stroesser wrote:
> The patch is tested, AFAICS, it works fine, i.e. sysemu can be switched on and
> off dynamically without crash.
> 
Here is a new version of the patch. I changed it to use TIF_SYSCALL_EMU
instead of TIF_SINGLETSTEP. This is more intuitive, I think.


Bodo

---

--- a/arch/i386/kernel/ptrace.c	2004-10-20 16:57:25.000000000 +0200
+++ b/arch/i386/kernel/ptrace.c	2004-10-21 09:55:00.000000000 +0200
@@ -585,7 +585,7 @@
  __attribute__((regparm(3)))
  int do_syscall_trace(struct pt_regs *regs, int entryexit)
  {
-	int is_sysemu;
+	int is_sysemu, is_systrace;
  	if (unlikely(current->audit_context)) {
  		if (!entryexit)
  			audit_syscall_entry(current, regs->orig_eax,
@@ -595,9 +595,19 @@
  			audit_syscall_exit(current, regs->eax);
  	}
  	is_sysemu = test_thread_flag(TIF_SYSCALL_EMU);
+	is_systrace = test_thread_flag(TIF_SYSCALL_TRACE);

-	if (!test_thread_flag(TIF_SYSCALL_TRACE) && !is_sysemu)
+	if (!is_systrace && !is_sysemu)
  		return 0;
+	/* We can detect the case of coming from PTRACE_SYSEMU and now
+	 * running with PTRACE_SYSCALL, by TIF_SYSCALL_EMU being set
+	 * additionally.
+	 * If so let's reset the flag and return without action.
+	 */
+	if (is_sysemu && is_systrace) {
+		clear_thread_flag(TIF_SYSCALL_EMU);
+		return 0;
+	}
  	if (!(current->ptrace & PT_PTRACED))
  		return 0;
  	/* the 0x80 provides a way for the tracing parent to distinguish
@@ -605,6 +615,15 @@
  	ptrace_notify(SIGTRAP | ((current->ptrace & PT_TRACESYSGOOD)
  				 ? 0x80 : 0));

+	/* If we came here with PTRACE_SYSEMU and now continue with
+	 * PTRACE_SYSCALL, entry.S used to intercept the syscall return. But it
+	 * shouldn't!
+	 * So we additionally use TIF_SYSCALL_EMU, which is always unused in this
+	 * special case, to remember, we came from SYSEMU.
+	 */
+	if (is_sysemu && test_thread_flag(TIF_SYSCALL_TRACE))
+		set_thread_flag(TIF_SYSCALL_EMU);
+
  	/*
  	 * this isn't the same as continuing with a signal, but it will do
  	 * for normal use.  strace only continues with a signal if the


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