Re: ptrace single-stepping change breaks Wine

Jesse Allen
2004-12-30T04:28:55Z

On Wed, 29 Dec 2004 16:44:05 -0800 (PST), Linus Torvalds
<torvalds@osdl.org> wrote:
>
> That still leaves the problem of the clearing of TF_MASK. I _appears_ that
> the problem is that TF was set both by Wine doing a PTRACE_SINGLESTEP
> (since PT_DTRACE is set) _and_ the application having TF enabled in eflags
> from before (since it seems to want to keep it enabled).
>
> How about something like the attachment for the TF_MASK issue (replacing
> your "don't clear" code)? The comments should make the intention pretty
> obvious, but I have equally obviously not actually _tested_ any of this..
>

The following patch works for me. I still have to remove
TIF_SINGLESTEP test. I also went ahead and tried adding the other fix
on the ptrace_notify call and _TIF_WORK_MASK, but for some reason,
changing _TIF_WORK_MASK seems to break the program now. This patch
does fix the TF clearing problem.

Jesse

--- linux/arch/i386/kernel/ptrace.c 2004-12-29 14:10:34.000000000 -0700
+++ linux-mod/arch/i386/kernel/ptrace.c 2004-12-29 20:50:00.000000000 -0700
@@ -142,18 +142,31 @@
{
long eflags;

+ /*
+ * Always set TIF_SINGLESTEP - this guarantees that
+ * we single-step system calls etc..
+ */
set_tsk_thread_flag(child, TIF_SINGLESTEP);
+
+ /*
+ * If TF was already set, don't do anything else
+ */
eflags = get_stack_long(child, EFL_OFFSET);
+ if (eflags & TRAP_FLAG)
+ return;
put_stack_long(child, EFL_OFFSET, eflags | TRAP_FLAG);
child->ptrace |= PT_DTRACE;
}

static void clear_singlestep(struct task_struct *child)
{
+ /* Always clear TIF_SINGLESTEP... */
+ clear_tsk_thread_flag(child, TIF_SINGLESTEP);
+
+ /* But touch TF only if it was set by us.. */
if (child->ptrace & PT_DTRACE) {
long eflags;

- clear_tsk_thread_flag(child, TIF_SINGLESTEP);
eflags = get_stack_long(child, EFL_OFFSET);
put_stack_long(child, EFL_OFFSET, eflags & ~TRAP_FLAG);
child->ptrace &= ~PT_DTRACE;
@@ -568,15 +581,13 @@
audit_syscall_exit(current, regs->eax);
}

- if (!test_thread_flag(TIF_SYSCALL_TRACE) &&
- !test_thread_flag(TIF_SINGLESTEP))
+ if (!test_thread_flag(TIF_SYSCALL_TRACE))
return;
if (!(current->ptrace & PT_PTRACED))
return;
/* the 0x80 provides a way for the tracing parent to distinguish
between a syscall stop and SIGTRAP delivery */
- ptrace_notify(SIGTRAP | ((current->ptrace & PT_TRACESYSGOOD) &&
- !test_thread_flag(TIF_SINGLESTEP) ? 0x80 : 0));
+ ptrace_notify(SIGTRAP | ((current->ptrace & PT_TRACESYSGOOD) ? 0x80 : 0));

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