[PATCH] powerpc: silence a -Wcast-function-type warning in dawr_write_file_bool

[PATCH] powerpc: silence a -Wcast-function-type warning in dawr_write_file_bool

[Mathieu Malaterre]

In commit c1fe190c0672 ("powerpc: Add force enable of DAWR on P9
option") the following piece of code was added:

   smp_call_function((smp_call_func_t)set_dawr, &null_brk, 0);

Since GCC 8 this trigger the following warning about incompatible
function types:

  arch/powerpc/kernel/hw_breakpoint.c:408:21: error: cast between incompatible function types from 'int (*)(struct arch_hw_breakpoint *)' to 'void (*)(void *)' [-Werror=cast-function-type]

Cast the function to an intermediate (void*) to make the compiler loose
knowledge about actual type.

Fixes: c1fe190c0672 ("powerpc: Add force enable of DAWR on P9 option")
Cc: Michael Neuling <mikey@neuling.org>
Signed-off-by: Mathieu Malaterre <malat@debian.org>
---
 arch/powerpc/kernel/hw_breakpoint.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/hw_breakpoint.c b/arch/powerpc/kernel/hw_breakpoint.c
index f70fb89dbf60..baeb4c58de3b 100644
--- a/arch/powerpc/kernel/hw_breakpoint.c
+++ b/arch/powerpc/kernel/hw_breakpoint.c
@@ -405,7 +405,8 @@ static ssize_t dawr_write_file_bool(struct file *file,
 
 	/* If we are clearing, make sure all CPUs have the DAWR cleared */
 	if (!dawr_force_enable)
-		smp_call_function((smp_call_func_t)set_dawr, &null_brk, 0);
+		smp_call_function((smp_call_func_t)(void *)set_dawr,
+				  &null_brk, 0);
 
 	return rc;
 }
-- 
2.20.1

Re: [PATCH] powerpc: silence a -Wcast-function-type warning in dawr_write_file_bool

[Christoph Hellwig]

On Wed, May 15, 2019 at 02:09:42PM +0200, Mathieu Malaterre wrote:
> In commit c1fe190c0672 ("powerpc: Add force enable of DAWR on P9
> option") the following piece of code was added:
> 
>    smp_call_function((smp_call_func_t)set_dawr, &null_brk, 0);
> 
> Since GCC 8 this trigger the following warning about incompatible
> function types:

And the warning is there for a reason, and should not be hidden
behind a cast.  This should instead be fixed by something like this:

diff --git a/arch/powerpc/kernel/hw_breakpoint.c b/arch/powerpc/kernel/hw_breakpoint.c
index da307dd93ee3..a26b67a1be83 100644
--- a/arch/powerpc/kernel/hw_breakpoint.c
+++ b/arch/powerpc/kernel/hw_breakpoint.c
@@ -384,6 +384,12 @@ void hw_breakpoint_pmu_read(struct perf_event *bp)
 bool dawr_force_enable;
 EXPORT_SYMBOL_GPL(dawr_force_enable);
 
+
+static void set_dawr_cb(void *info)
+{
+	set_dawr(info);
+}
+
 static ssize_t dawr_write_file_bool(struct file *file,
 				    const char __user *user_buf,
 				    size_t count, loff_t *ppos)
@@ -403,7 +409,7 @@ static ssize_t dawr_write_file_bool(struct file *file,
 
 	/* If we are clearing, make sure all CPUs have the DAWR cleared */
 	if (!dawr_force_enable)
-		smp_call_function((smp_call_func_t)set_dawr, &null_brk, 0);
+		smp_call_function(set_dawr_cb, &null_brk, 0);
 
 	return rc;
 }

Re: [PATCH] powerpc: silence a -Wcast-function-type warning in dawr_write_file_bool

[Mathieu Malaterre]

Hi Christoph,

On Wed, May 15, 2019 at 3:14 PM Christoph Hellwig <hch@infradead.org> wrote:
>
> On Wed, May 15, 2019 at 02:09:42PM +0200, Mathieu Malaterre wrote:
> > In commit c1fe190c0672 ("powerpc: Add force enable of DAWR on P9
> > option") the following piece of code was added:
> >
> >    smp_call_function((smp_call_func_t)set_dawr, &null_brk, 0);
> >
> > Since GCC 8 this trigger the following warning about incompatible
> > function types:
>
> And the warning is there for a reason, and should not be hidden
> behind a cast.  This should instead be fixed by something like this:

<meme: I have no idea what I am doing>
OK, thanks for the quick feedback, will send a v2 asap.

> diff --git a/arch/powerpc/kernel/hw_breakpoint.c b/arch/powerpc/kernel/hw_breakpoint.c
> index da307dd93ee3..a26b67a1be83 100644
> --- a/arch/powerpc/kernel/hw_breakpoint.c
> +++ b/arch/powerpc/kernel/hw_breakpoint.c
> @@ -384,6 +384,12 @@ void hw_breakpoint_pmu_read(struct perf_event *bp)
>  bool dawr_force_enable;
>  EXPORT_SYMBOL_GPL(dawr_force_enable);
>
> +
> +static void set_dawr_cb(void *info)
> +{
> +       set_dawr(info);
> +}
> +
>  static ssize_t dawr_write_file_bool(struct file *file,
>                                     const char __user *user_buf,
>                                     size_t count, loff_t *ppos)
> @@ -403,7 +409,7 @@ static ssize_t dawr_write_file_bool(struct file *file,
>
>         /* If we are clearing, make sure all CPUs have the DAWR cleared */
>         if (!dawr_force_enable)
> -               smp_call_function((smp_call_func_t)set_dawr, &null_brk, 0);
> +               smp_call_function(set_dawr_cb, &null_brk, 0);
>
>         return rc;
>  }

[PATCH v2] powerpc: silence a -Wcast-function-type warning in dawr_write_file_bool

[Mathieu Malaterre]

In commit c1fe190c0672 ("powerpc: Add force enable of DAWR on P9
option") the following piece of code was added:

   smp_call_function((smp_call_func_t)set_dawr, &null_brk, 0);

Since GCC 8 this triggers the following warning about incompatible
function types:

  arch/powerpc/kernel/hw_breakpoint.c:408:21: error: cast between incompatible function types from 'int (*)(struct arch_hw_breakpoint *)' to 'void (*)(void *)' [-Werror=cast-function-type]

Since the warning is there for a reason, and should not be hidden behind
a cast, provide an intermediate callback function to avoid the warning.

Fixes: c1fe190c0672 ("powerpc: Add force enable of DAWR on P9 option")
Suggested-by: Christoph Hellwig <hch@infradead.org>
Cc: Michael Neuling <mikey@neuling.org>
Signed-off-by: Mathieu Malaterre <malat@debian.org>
---
v2: do not hide warning using a hack

 arch/powerpc/kernel/hw_breakpoint.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/hw_breakpoint.c b/arch/powerpc/kernel/hw_breakpoint.c
index f70fb89dbf60..969092d84a2f 100644
--- a/arch/powerpc/kernel/hw_breakpoint.c
+++ b/arch/powerpc/kernel/hw_breakpoint.c
@@ -386,6 +386,11 @@ void hw_breakpoint_pmu_read(struct perf_event *bp)
 bool dawr_force_enable;
 EXPORT_SYMBOL_GPL(dawr_force_enable);
 
+static void set_dawr_cb(void *info)
+{
+	set_dawr(info);
+}
+
 static ssize_t dawr_write_file_bool(struct file *file,
 				    const char __user *user_buf,
 				    size_t count, loff_t *ppos)
@@ -405,7 +410,7 @@ static ssize_t dawr_write_file_bool(struct file *file,
 
 	/* If we are clearing, make sure all CPUs have the DAWR cleared */
 	if (!dawr_force_enable)
-		smp_call_function((smp_call_func_t)set_dawr, &null_brk, 0);
+		smp_call_function(set_dawr_cb, &null_brk, 0);
 
 	return rc;
 }
-- 
2.20.1