lkml.org 
[lkml]   [2011]   [May]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: [PATCH] kernel: Fix ftrace.c compiler warning when calling ftrace_nop_replace()


On Mon, 23 May 2011, Steven Rostedt wrote:

> On Sun, 2011-05-22 at 18:36 -0700, H. Peter Anvin wrote:
> > On 05/22/2011 06:19 PM, Eduardo Silva wrote:
> > > the function ftrace_nop_replace() returns a 'static const unsigned char *'
> > > value, so when the caller perform a direct assignment to a
> > > 'static unsigned char *', the compiler raise the following warning message:
> > >
> > > ftrace.c:308:6: warning: assignment discards qualifiers from pointer target type
> > > ftrace.c:318:6: warning: assignment discards qualifiers from pointer target type
> > >
> > > Adding the proper casts the message goes away.
> > >
> > > Signed-off-by: Eduardo Silva <edsiper@gmail.com>
> >
> > This quiets a warning of something that potentially looks like a real
> > bug. Perhaps "new" should be const?
>
> Although there is no real bug here, I hate these "hide the warning"
> patches.
>
> The real solution is to change all the users into const *. This should
> be doable as the new and old pointers are not modified.
>
> And remember:
>
> char *changes;
> const char *no_changes;
>
> no_changes = changes; /* is OK! (no compiler warnings) */
>
> changes = no_changes; /* is not OK. (compiler will warn). */
>
> -- Steve

The following needs some testing, just compile tested for now.

From 71d6e5971cc90a03fd2d7bf8aaa2b81932bd0c7c Mon Sep 17 00:00:00 2001
From: John Kacur <jkacur@redhat.com>
Date: Mon, 23 May 2011 21:24:27 +0200
Subject: [PATCH] ftrace: Change unsigned char *new, *old to const
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

This removes the warning:
arch/x86/kernel/ftrace.c: In function ‘ftrace_make_nop’:
/arch/x86/kernel/ftrace.c:308: warning: assignment discards qualifiers from pointer target type

Steven Rostedt suggested to make these pointers const pointers.

This patch assumes that
https://patchwork.kernel.org/patch/798172/
is applied first.

Reported-by: Eduardo Silva <edsiper@gmail.com>
Signed-off-by: John Kacur <jkacur@redhat.com>
---
arch/x86/kernel/ftrace.c | 12 ++++++------
1 files changed, 6 insertions(+), 6 deletions(-)
diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index 0ba15a6..e4f23d1 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -123,7 +123,7 @@ static unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr)
static atomic_t nmi_running = ATOMIC_INIT(0);
static int mod_code_status; /* holds return value of text write */
static void *mod_code_ip; /* holds the IP to write to */
-static void *mod_code_newcode; /* holds the text to write to the IP */
+static const void *mod_code_newcode; /* holds the text to write to the IP */

static unsigned nmi_wait_count;
static atomic_t nmi_update_count = ATOMIC_INIT(0);
@@ -225,7 +225,7 @@ within(unsigned long addr, unsigned long start, unsigned long end)
}

static int
-do_ftrace_mod_code(unsigned long ip, void *new_code)
+do_ftrace_mod_code(unsigned long ip, const void *new_code)
{
/*
* On x86_64, kernel text mappings are mapped read-only with
@@ -266,8 +266,8 @@ static const unsigned char *ftrace_nop_replace(void)
}

static int
-ftrace_modify_code(unsigned long ip, unsigned char *old_code,
- unsigned char *new_code)
+ftrace_modify_code(unsigned long ip, const unsigned char *old_code,
+ const unsigned char *new_code)
{
unsigned char replaced[MCOUNT_INSN_SIZE];

@@ -301,7 +301,7 @@ ftrace_modify_code(unsigned long ip, unsigned char *old_code,
int ftrace_make_nop(struct module *mod,
struct dyn_ftrace *rec, unsigned long addr)
{
- unsigned char *new, *old;
+ const unsigned char *new, *old;
unsigned long ip = rec->ip;

old = ftrace_call_replace(ip, addr);
@@ -312,7 +312,7 @@ int ftrace_make_nop(struct module *mod,

int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
{
- unsigned char *new, *old;
+ const unsigned char *new, *old;
unsigned long ip = rec->ip;

old = ftrace_nop_replace();
--
1.7.2.3
\
 
 \ /
  Last update: 2011-05-23 22:03    [from the cache]
©2003-2011 Jasper Spaans