Re: [PATCH] x86-64 singlestep through sigreturn system call

[Roland McGrath <roland@redhat.com>]

> Hmm, but now the behaviour for 32bit processes is different from the
> native 32bit kernel, since 32bit didn't apply any patch so far AFAIK.

Well, I was (and am) advocating that Davide's patch for native 32-bit be
applied as well.  If it is, then my last x86-64 patch covers both 32-bit
and 64-bit cases with minimal cruft.  In particular, 2.6.8-rc1-mm1 contains
Davide's patch and both of my earlier x86-64 patches.  I hope Andrew will
replace those two patches with the later cleaner single x86-64 patch.  If
Linus merges that patch of mine and Davide's i386 patch, I will be a happy
camper.

> If you send me a patch that just changes the behaviour of 64bit 
> IRET I would apply it.

Ok.  This is just one line different from the patch I just posted.  In
32-bit processes, some ptrace operations will superfluously clear a flag
bit that can never be set, rather than test another flag bit to branch
around doing it.  If/when the native 32-bit behavior fix gets merged in and
you want to match it, just remove `if (!test_tsk_thread_flag(child, TIF_IA32))'
(which is the same as reverting this patch and applying the earlier one).


Thanks,
Roland


Index: linux-2.6/arch/x86_64/kernel/entry.S
===================================================================
RCS file: /home/roland/redhat/bkcvs/linux-2.5/arch/x86_64/kernel/entry.S,v
retrieving revision 1.22
diff -b -p -u -r1.22 entry.S
--- linux-2.6/arch/x86_64/kernel/entry.S 12 Apr 2004 20:29:12 -0000 1.22
+++ linux-2.6/arch/x86_64/kernel/entry.S 15 Jul 2004 23:45:59 -0000
@@ -297,7 +297,7 @@ int_very_careful:
 	sti
 	SAVE_REST
 	/* Check for syscall exit trace */	
-	testl $(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT),%edx
+	testl $(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT|_TIF_SINGLESTEP),%edx
 	jz int_signal
 	pushq %rdi
 	leaq 8(%rsp),%rdi	# &ptregs -> arg1	
Index: linux-2.6/ptrace.c
===================================================================
RCS file: /home/roland/redhat/bkcvs/linux-2.5/arch/x86_64/kernel/ptrace.c,v
retrieving revision 1.16
diff -u -b -p -r1.16 ptrace.c
--- linux-2.6/ptrace.c 31 May 2004 03:07:42 -0000 1.16
+++ linux-2.6/ptrace.c 22 Jul 2004 00:42:06 -0000
@@ -88,6 +88,7 @@ void ptrace_disable(struct task_struct *
 { 
 	long tmp;
 
+	clear_tsk_thread_flag(child, TIF_SINGLESTEP);
 	tmp = get_stack_long(child, EFL_OFFSET) & ~TRAP_FLAG;
 	put_stack_long(child, EFL_OFFSET, tmp);
 }
@@ -344,6 +345,7 @@ asmlinkage long sys_ptrace(long request,
 			set_tsk_thread_flag(child,TIF_SYSCALL_TRACE);
 		else
 			clear_tsk_thread_flag(child,TIF_SYSCALL_TRACE);
+		clear_tsk_thread_flag(child, TIF_SINGLESTEP);
 		child->exit_code = data;
 	/* make sure the single step bit is not set. */
 		tmp = get_stack_long(child, EFL_OFFSET);
@@ -395,6 +397,7 @@ asmlinkage long sys_ptrace(long request,
 		ret = 0;
 		if (child->state == TASK_ZOMBIE)	/* already dead */
 			break;
+		clear_tsk_thread_flag(child, TIF_SINGLESTEP);
 		child->exit_code = SIGKILL;
 		/* make sure the single step bit is not set. */
 		tmp = get_stack_long(child, EFL_OFFSET) & ~TRAP_FLAG;
@@ -416,6 +419,8 @@ asmlinkage long sys_ptrace(long request,
 		}
 		tmp = get_stack_long(child, EFL_OFFSET) | TRAP_FLAG;
 		put_stack_long(child, EFL_OFFSET, tmp);
+		if (!test_tsk_thread_flag(child, TIF_IA32))
+			set_tsk_thread_flag(child, TIF_SINGLESTEP);
 		child->exit_code = data;
 		/* give it a chance to run. */
 		wake_up_process(child);
@@ -528,7 +533,8 @@ asmlinkage void syscall_trace_leave(stru
 	if (unlikely(current->audit_context))
 		audit_syscall_exit(current, regs->rax);
 
-	if (test_thread_flag(TIF_SYSCALL_TRACE)
+	if ((test_thread_flag(TIF_SYSCALL_TRACE)
+	     || test_thread_flag(TIF_SINGLESTEP))
 	    && (current->ptrace & PT_PTRACED))
 		syscall_trace(regs);
 }