Re: [uml-devel] Re: [patch 1/1] SYSEMU: avoid intercepting syscall on return when using SYSCALL again.

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

Blaisorblade wrote:
> No. Just strace any process inside UML. Let's "strace ls". Last time I 
> checked, it does not work. Oh hell! It works (as of 2.6.9)! Well, you already 
> fixed that.
> 
No. Here you are wrong. The problem is still there (or is it again there?).
Sorry.

My latest patch "patch-singlestep-sighdlr" has been too complete!
Setting TIF_SIGPENDING after ptrace_notify() in syscall_trace() in neccessary
only on the 2nd tracepoint (entryexit == 1).
And setting it on the 1st tracepoint lets some specific systemcalls loop.
Example: sys_rt_sigaction() wants to be called without SIGPENDING. Thus it returns
with -ERESTARTNOINTR. On return do_signal() is called, which resets TIF_SIGPENDING
and sets EIP back to the syscall. Now the syscall starts, runs through
syscall_trace() and TIF_SIGPENDING is set again. Now it returns with -ERESTARTNOINTR
...
...

Here's the patch:

---

--- a/arch/um/kernel/ptrace.c	2004-10-29 02:27:42.000000000 +0200
+++ b/arch/um/kernel/ptrace.c	2004-10-29 02:28:24.000000000 +0200
@@ -330,7 +330,8 @@ void syscall_trace(union uml_pt_regs *re
  	   between a syscall stop and SIGTRAP delivery */
  	ptrace_notify(SIGTRAP | (((current->ptrace & PT_TRACESYSGOOD) &&
  				 !is_singlestep) ? SYSCALL_TRAP : 0));
-	set_thread_flag(TIF_SIGPENDING); /* force do_signal() --> is_syscall() */
+	if ( entryexit ) /* force do_signal() --> is_syscall() */
+		set_thread_flag(TIF_SIGPENDING);

  	/*
  	 * this isn't the same as continuing with a signal, but it will do



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