[PATCH] Silence an uninitialized variable warning

[PATCH] Silence an uninitialized variable warning

[Dan Carpenter]

Smatch complains that "ret" could be uninitialized if we don't enter the
loop.  I don't know if that's possible, but it's nicer to return a
literal zero instead.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
---
 kernel/trace/trace_syscalls.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
index 73140d80dd46..63528f458826 100644
--- a/kernel/trace/trace_syscalls.c
+++ b/kernel/trace/trace_syscalls.c
@@ -286,7 +286,7 @@ static int __init syscall_enter_define_fields(struct trace_event_call *call)
 		offset += sizeof(unsigned long);
 	}
 
-	return ret;
+	return 0;
 }
 
 static void ftrace_syscall_enter(void *data, struct pt_regs *regs, long id)
-- 
2.11.0

Re: [PATCH] Silence an uninitialized variable warning

[Steven Rostedt]

On Tue, 26 Nov 2019 15:19:34 +0300
Dan Carpenter <dan.carpenter@oracle.com> wrote:

> Smatch complains that "ret" could be uninitialized if we don't enter the
> loop.  I don't know if that's possible, but it's nicer to return a
> literal zero instead.
> 
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> ---
>  kernel/trace/trace_syscalls.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
> index 73140d80dd46..63528f458826 100644
> --- a/kernel/trace/trace_syscalls.c
> +++ b/kernel/trace/trace_syscalls.c
> @@ -286,7 +286,7 @@ static int __init syscall_enter_define_fields(struct trace_event_call *call)
>  		offset += sizeof(unsigned long);
>  	}
>  
> -	return ret;
> +	return 0;
>  }
>  
>  static void ftrace_syscall_enter(void *data, struct pt_regs *regs, long id)

The current code has this:

static int __init syscall_enter_define_fields(struct trace_event_call *call)
{
	struct syscall_trace_enter trace;
	struct syscall_metadata *meta = call->data;
	int ret;
	int i;
	int offset = offsetof(typeof(trace), args);

	ret = trace_define_field(call, SYSCALL_FIELD(int, nr, __syscall_nr),
				 FILTER_OTHER);
	if (ret)
		return ret;

	for (i = 0; i < meta->nb_args; i++) {
		ret = trace_define_field(call, meta->types[i],
					 meta->args[i], offset,
					 sizeof(unsigned long), 0,
					 FILTER_OTHER);
		offset += sizeof(unsigned long);
	}

	return ret;
}


How can ret possibly be uninitialized?

-- Steve

Re: [PATCH] Silence an uninitialized variable warning

[Dan Carpenter]

On Wed, Dec 04, 2019 at 09:26:40AM -0500, Steven Rostedt wrote:
> On Tue, 26 Nov 2019 15:19:34 +0300
> Dan Carpenter <dan.carpenter@oracle.com> wrote:
> 
> > Smatch complains that "ret" could be uninitialized if we don't enter the
> > loop.  I don't know if that's possible, but it's nicer to return a
> > literal zero instead.
> > 
> > Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> > ---
> >  kernel/trace/trace_syscalls.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
> > index 73140d80dd46..63528f458826 100644
> > --- a/kernel/trace/trace_syscalls.c
> > +++ b/kernel/trace/trace_syscalls.c
> > @@ -286,7 +286,7 @@ static int __init syscall_enter_define_fields(struct trace_event_call *call)
> >  		offset += sizeof(unsigned long);
> >  	}
> >  
> > -	return ret;
> > +	return 0;
> >  }
> >  
> >  static void ftrace_syscall_enter(void *data, struct pt_regs *regs, long id)
> 
> The current code has this:
> 
> static int __init syscall_enter_define_fields(struct trace_event_call *call)
> {
> 	struct syscall_trace_enter trace;
> 	struct syscall_metadata *meta = call->data;
> 	int ret;
> 	int i;
> 	int offset = offsetof(typeof(trace), args);
> 
> 	ret = trace_define_field(call, SYSCALL_FIELD(int, nr, __syscall_nr),
> 				 FILTER_OTHER);

In linux-next this ret = trace_define_field() assignment is removed.
That was commit 60fdad00827c ("ftrace: Rework event_create_dir()").

> 	if (ret)
> 		return ret;
> 
> 	for (i = 0; i < meta->nb_args; i++) {
> 		ret = trace_define_field(call, meta->types[i],
> 					 meta->args[i], offset,
> 					 sizeof(unsigned long), 0,
> 					 FILTER_OTHER);
> 		offset += sizeof(unsigned long);
> 	}
> 
> 	return ret;
> }
> 
> 
> How can ret possibly be uninitialized?

I should have written this commit more carefully and verified whether
meta->nb_args can actually be zero instead of just assuming it was a
false positive...

regards,
dan carpenter

Re: [PATCH] Silence an uninitialized variable warning

[Peter Zijlstra]

On Wed, Dec 04, 2019 at 09:42:47PM +0300, Dan Carpenter wrote:

> > The current code has this:
> > 
> > static int __init syscall_enter_define_fields(struct trace_event_call *call)
> > {
> > 	struct syscall_trace_enter trace;
> > 	struct syscall_metadata *meta = call->data;
> > 	int ret;
> > 	int i;
> > 	int offset = offsetof(typeof(trace), args);
> > 
> > 	ret = trace_define_field(call, SYSCALL_FIELD(int, nr, __syscall_nr),
> > 				 FILTER_OTHER);
> 
> In linux-next this ret = trace_define_field() assignment is removed.
> That was commit 60fdad00827c ("ftrace: Rework event_create_dir()").

Yep, mea culpa.

> > 	if (ret)
> > 		return ret;
> > 
> > 	for (i = 0; i < meta->nb_args; i++) {
> > 		ret = trace_define_field(call, meta->types[i],
> > 					 meta->args[i], offset,
> > 					 sizeof(unsigned long), 0,
> > 					 FILTER_OTHER);
> > 		offset += sizeof(unsigned long);
> > 	}
> > 
> > 	return ret;
> > }
> > 
> > 
> > How can ret possibly be uninitialized?
> 
> I should have written this commit more carefully and verified whether
> meta->nb_args can actually be zero instead of just assuming it was a
> false positive...

Right, I'm thinking this is in fact possible. We have syscalls without
arguments (sys_sched_yield for exmaple).

Re: [PATCH] Silence an uninitialized variable warning

[Dan Carpenter]

On Thu, Dec 05, 2019 at 10:32:29AM +0100, Peter Zijlstra wrote:
> On Wed, Dec 04, 2019 at 09:42:47PM +0300, Dan Carpenter wrote:
> 
> > > The current code has this:
> > > 
> > > static int __init syscall_enter_define_fields(struct trace_event_call *call)
> > > {
> > > 	struct syscall_trace_enter trace;
> > > 	struct syscall_metadata *meta = call->data;
> > > 	int ret;
> > > 	int i;
> > > 	int offset = offsetof(typeof(trace), args);
> > > 
> > > 	ret = trace_define_field(call, SYSCALL_FIELD(int, nr, __syscall_nr),
> > > 				 FILTER_OTHER);
> > 
> > In linux-next this ret = trace_define_field() assignment is removed.
> > That was commit 60fdad00827c ("ftrace: Rework event_create_dir()").
> 
> Yep, mea culpa.
> 
> > > 	if (ret)
> > > 		return ret;
> > > 
> > > 	for (i = 0; i < meta->nb_args; i++) {
> > > 		ret = trace_define_field(call, meta->types[i],
> > > 					 meta->args[i], offset,
> > > 					 sizeof(unsigned long), 0,
> > > 					 FILTER_OTHER);
> > > 		offset += sizeof(unsigned long);
> > > 	}
> > > 
> > > 	return ret;
> > > }
> > > 
> > > 
> > > How can ret possibly be uninitialized?
> > 
> > I should have written this commit more carefully and verified whether
> > meta->nb_args can actually be zero instead of just assuming it was a
> > false positive...
> 
> Right, I'm thinking this is in fact possible. We have syscalls without
> arguments (sys_sched_yield for exmaple).

Well, it would have triggered a run time bug because of that thing with
GCC where it sometimes initializes variables to zero.

Let me resend properly with a Fixes tag.

regards,
dan carpenter