vcgencmd: Avoid compiler complaints

[popcornmix]

Latest compilers are more fussy and this doesn't build with debian build scripts. Fix this.

[popcornmix]

@XECDesign does this fix your build issues?

[pelwell]

See #64.

[popcornmix]

Okay - dropped eeptools commit.

[XECDesign]

Seems to build, yeah.

[XECDesign]

I can update the package once this is merged.

[popcornmix]

@pelwell is this okay?

[pelwell]

I don't understand (without seeing the errors) why memset (which will happily copy beyond the end of the string) is somehow more acceptable than strncpy, but I'm happy for this to be merged.

[XECDesign]

Full disclosure: I didn't try building from head of tree without this commit. So if there's a chance it's not needed, I can try without it.

Update: seems happy without it.

[XECDesign]

I was curious why it wasn't failing and it looks like some cmake files have this line: set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wall -Wextra -Werror -pedantic")

vcgencmd doesn't, so it only inherits the CFLAGS passed down by Debian's build system - CFLAGS=-g -O2 -ffile-prefix-map=<snip>=. -fstack-protector-strong -Wformat -Werror=format-security

[popcornmix]

I don't understand (without seeing the errors) why memset (which will happily copy beyond the end of the string) is somehow more acceptable than strncpy, but I'm happy for this to be merged.

In the commit message was the error:

In file included from /usr/include/string.h:535,
from /<>/vcgencmd/vcgencmd.c:34:
In function ‘strncat’,
inlined from ‘gencmd’ at /<>/vcgencmd/vcgencmd.c:109:4,
inlined from ‘main’ at /<>/vcgencmd/vcgencmd.c:152:14:
/usr/include/arm-linux-gnueabihf/bits/string_fortified.h:138:10: warning: ‘__builtin___strncat_chk’ specified bound 1024 equals destination size [-Wstringop-overflow=]
138 | return __builtin___strncat_chk (__dest, __src, __len,
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
139 | __glibc_objsize (__dest));
| ~~~~~~~~~~~~~~~~~~~~~~~~~

it seems strncat triggers some additional bounds checking that memcpy does not.

[chewi]

Please can we not include -Werror in the default flags as it's a pain for both distributions and users building themselves. Perhaps we could only add it when CMAKE_BUILD_TYPE is Debug.