Re: [RFC patch] vsprintf: Allow %pe to print non PTR_ERR %pe uses as decimal

On Wed, 2021-03-24 at 18:33 +0100, Rasmus Villemoes wrote:

On 24/03/2021 18.20, Joe Perches wrote:

quoted

On Wed, 2021-03-24 at 09:52 -0700, Joe Perches wrote:

quoted

On Wed, 2021-03-24 at 17:42 +0100, Arnd Bergmann wrote:

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On Wed, Mar 24, 2021 at 3:20 PM Joe Perches [off-list ref] wrote:

[]

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diff --git a/drivers/gpu/drm/imx/imx-ldb.c b/drivers/gpu/drm/imx/imx-ldb.c

[]

quoted

@@ -197,6 +197,12 @@ static void imx_ldb_encoder_enable(struct drm_encoder *encoder)

      int dual = ldb->ldb_ctrl & LDB_SPLIT_MODE_EN;
      int mux = drm_of_encoder_active_port_id(imx_ldb_ch->child, encoder);

+     if (mux < 0 || mux >= ARRAY_SIZE(ldb->clk_sel)) {
+             dev_warn(ldb->dev, "%s: invalid mux %d\n",
+                      __func__, ERR_PTR(mux));

This does not compile without warnings.

drivers/gpu/drm/imx/imx-ldb.c: In function ‘imx_ldb_encoder_enable’:
drivers/gpu/drm/imx/imx-ldb.c:201:22: warning: format ‘%d’ expects argument of type ‘int’, but argument 4 has type ‘void *’ [-Wformat=]
  201 |   dev_warn(ldb->dev, "%s: invalid mux %d\n",
      |                      ^~~~~~~~~~~~~~~~~~~~~~

If you want to use ERR_PTR, the %d should be %pe as ERR_PTR
is converting an int a void * to decode the error type and
emit it as a string.

Sorry about that.

I decided against using ERR_PTR() in order to also check for
positive array overflow, but the version I tested was different from
the version I sent.

v3 coming.

Thanks.  No worries.

Up to you, vsprintf would emit the positive mux as a funky hashed
hex value by default if you use ERR_PTR with mux > ARRAY_SIZE so
perhaps %d without the ERR_PTR use makes the most sense.

quoted

Maybe it's better to output non PTR_ERR %pe uses as decimal so this
sort of code would work.

No, because that would leak the pointer value when somebody has
accidentally passed a real kernel pointer to %pe.

I think it's not really an issue.

_All_ code that uses %p<foo> extensions need inspection anyway.

It's already possible to intentionally 'leak' the ptr value
by using %pe, -ptr so I think that's not really an issue.

If the code wants a cute -EFOO string explaining what's wrong, what
about "%pe", ERR_PTR(mux < 0 : mux : -ERANGE)? Or two separate error
messages

if (mux < 0)
  ...
else if (mux >= ARRAY_SIZE())
  ...

Multiple tests, more unnecessary code, multiple format strings, etc...



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