Hi

On 22.10.20 01:06, Laurent Pinchart wrote:

Hi Thomas,

Thank you for the patch.

On Wed, Oct 21, 2020 at 02:12:41PM +0200, Thomas Zimmermann wrote:

quoted

Trying to copy into the string fields with strncpy() gives a warning from
gcc. Both fields are part of a packed HDMI header and do not require a
terminating \0 character.

../drivers/video/hdmi.c: In function 'hdmi_spd_infoframe_init':
../drivers/video/hdmi.c:230:2: warning: 'strncpy' specified bound 8 equals destination size [-Wstringop-truncation]
  230 |  strncpy(frame->vendor, vendor, sizeof(frame->vendor));
      |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../drivers/video/hdmi.c:231:2: warning: 'strncpy' specified bound 16 equals destination size [-Wstringop-truncation]
  231 |  strncpy(frame->product, product, sizeof(frame->product));
      |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Just use memcpy() instead.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
---
 drivers/video/hdmi.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/video/hdmi.c b/drivers/video/hdmi.c
index b7a1d6fae90d..1e4cb63d0d11 100644
--- a/drivers/video/hdmi.c
+++ b/drivers/video/hdmi.c

@@ -221,14 +221,18 @@ EXPORT_SYMBOL(hdmi_avi_infoframe_pack);
 int hdmi_spd_infoframe_init(struct hdmi_spd_infoframe *frame,
 			    const char *vendor, const char *product)
 {
+	size_t len;
+
 	memset(frame, 0, sizeof(*frame));
 
 	frame->type = HDMI_INFOFRAME_TYPE_SPD;
 	frame->version = 1;
 	frame->length = HDMI_SPD_INFOFRAME_SIZE;
 
-	strncpy(frame->vendor, vendor, sizeof(frame->vendor));
-	strncpy(frame->product, product, sizeof(frame->product));
+	len = strlen(vendor);
+	memcpy(frame->vendor, vendor, min(len, sizeof(frame->vendor)));
+	len = strlen(product);
+	memcpy(frame->product, product, min(len, sizeof(frame->product)));

As this seems to be a legitimate use of strncpy(), isn't there a way to
silence the warning without requiring this additional runtime complexity
?

Yes, the original code this correct. I looked through include/string.h
if there's better string function, but none fits. Most of them
0-terminate the output string.

The only simple fix seems to be to set gcc's -Wno-stringop-truncation
here. I'd expect that would be an even less preferable change.

Best regards
Thomas

quoted

 
 	return 0;
 }

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer