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Date: Fri, 11 May 2012 23:27:13 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Raphael Santana carvalho <utroz@...coders.com>
Cc: fweisbec@...il.com, mingo@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] kernel/trace: gcc warning: uninitialized variable.
On Fri, 2012-05-11 at 23:08 -0400, Steven Rostedt wrote:
> On Fri, 2012-05-11 at 23:26 -0300, Raphael Santana carvalho wrote:
> > >From 2f1490c5e8e2a393d9376d959e2ff6836757f51a Mon Sep 17 00:00:00 2001
> > From: Raphael S.Carvalho <utroz@...coders.com>
> > Date: Fri, 11 May 2012 22:58:43 -0300
> > Subject: [PATCH 1/1] kernel/trace: gcc warning: uninitialized variable.
> >
> > I've received a problem in this file when I was compiling my own kernel.
> > It's a simple uninitialized variable, so that gcc is warning about it.
> >
> > The function is actually working correctly, because it's impossible to use the
> > variable(page2) uninitialized because it's only referenced if nr_pages == 2,
> > and we will have previously set it in that case.
>
> Correct.
>
> >
> > gcc version 4.5.2 (GCC) - Follows the warning:
>
> It's a bug in gcc. If you use gcc 4.6 or later it does not warn.
>
> As this code may change in the future, I don't want to hide errors that
> gcc 4.6 could catch. Thus I'm not going to take this patch.
>
> Don't feel bad, you're probably the 5th person I declined this change
> from. At least you noticed that it was just gcc complaining and did not
> blindly set the variable to NULL.
Although, this patch here cleans up the code slightly and should get rid
of the warning.
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 2a22255..d77b481 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3749,14 +3749,14 @@ tracing_mark_write(struct file *filp, const char __user *ubuf,
struct print_entry *entry;
unsigned long irq_flags;
struct page *pages[2];
+ void *map_page[2];
int nr_pages = 1;
ssize_t written;
- void *page1;
- void *page2;
int offset;
int size;
int len;
int ret;
+ int i;
if (tracing_disabled)
return -EINVAL;
@@ -3795,9 +3795,8 @@ tracing_mark_write(struct file *filp, const char __user *ubuf,
goto out;
}
- page1 = kmap_atomic(pages[0]);
- if (nr_pages == 2)
- page2 = kmap_atomic(pages[1]);
+ for (i = 0; i < nr_pages; i++)
+ map_page[i] = kmap_atomic(pages[i]);
local_save_flags(irq_flags);
size = sizeof(*entry) + cnt + 2; /* possible \n added */
@@ -3815,10 +3814,10 @@ tracing_mark_write(struct file *filp, const char __user *ubuf,
if (nr_pages == 2) {
len = PAGE_SIZE - offset;
- memcpy(&entry->buf, page1 + offset, len);
- memcpy(&entry->buf[len], page2, cnt - len);
+ memcpy(&entry->buf, map_page[0] + offset, len);
+ memcpy(&entry->buf[len], map_page[1], cnt - len);
} else
- memcpy(&entry->buf, page1 + offset, cnt);
+ memcpy(&entry->buf, map_page[0] + offset, cnt);
if (entry->buf[cnt - 1] != '\n') {
entry->buf[cnt] = '\n';
@@ -3833,11 +3832,10 @@ tracing_mark_write(struct file *filp, const char __user *ubuf,
*fpos += written;
out_unlock:
- if (nr_pages == 2)
- kunmap_atomic(page2);
- kunmap_atomic(page1);
- while (nr_pages > 0)
- put_page(pages[--nr_pages]);
+ for (i = 0; i < nr_pages; i++){
+ kunmap_atomic(map_page[i]);
+ put_page(pages[i]);
+ }
out:
return written;
}
--
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