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:

...

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

...

return 0; }

Hi

Am 01.11.20 um 10:50 schrieb Sam Ravnborg:

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

...

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

I assume vendor is guaranteed to be 0-termindated.

It's a fixed-length field in the protocol. There's similar code in radeon IIRC. So it would be nice to disable the warning in these cases. But that's probably to much fiddling.

Reviewed-by: Sam Ravnborg sam@ravnborg.org

Thanks.

Best regards Thomas

...

---

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)));

  return 0;

}

2.28.0

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