warning: implicit declaration of function 'sbrk' and 'strdup'

[fordfrog]

while installing latest (20160531) raspberrypi-userland on gentoo, i got these QA warnings:

 * QA Notice: Package triggers severe warnings which indicate that it
 *            may exhibit random runtime failures.
 * /var/tmp/portage/media-libs/raspberrypi-userland-0_pre20160531/work/raspberrypi-userland-ed59ee1/interface/vcos/pthreads/vcos_platform.h:777:4: warning: implicit declaration of function ‘sbrk’ [-Wimplicit-function-declaration]
 * /var/tmp/portage/media-libs/raspberrypi-userland-0_pre20160531/work/raspberrypi-userland-ed59ee1/interface/vcos/pthreads/vcos_platform.h:818:4: warning: implicit declaration of function ‘strdup’ [-Wimplicit-function-declaration]

i don't know whether it is intended or it should be fixed so can someone who knows this stuff please clarify it?

[fordfrog]

i found this info: http://stackoverflow.com/questions/8440816/warning-implicit-declaration-of-function

so it means that these two functions are used before they are declared (either in header file or before they are first used).

[popcornmix]

sbrk should be declared in <unistd.h> which is being included. strdup should be declared in <string.h> which is being included. I'm not sure if the gentoo compiler doesn't support these?

I don't think sbrk or strdup are typically used by userland (mostly for test functions), and the lack of a declaration for a function with simple types is normally not fatal, so it's probably not a big issue.

@6by9 @pelwell any thoughts?

[pelwell]

strdup is part of POSIX so ought to be included. sbrk has been removed, so perhaps that failure is more understandable. Which compiler (including version) are you using?

[ED6E0F17]

I have seen this error previously, and now that I have checked "string,h" on wheezy I understand why.

[ED6E0F17]

It look as though "_GNU_SOURCE" needs to be defined to get "USE_XOPEN_EXTENDED", and then define sbrk and strdup. "_GNU_SOURCE" is defined in some places, but not everywhere that it is needed.

[fordfrog]

@pelwell gcc 4.9.3

[ED6E0F17]

It becomes an issue when the compiler is throwing so many warnings that you stop reading them, and warning is given every time that "vcos.h" is included. Most of these seem to be in the "containers" directory, which defines POSIX level 2001, but strdup requires POSIX level 2008: https://github.com/raspberrypi/userland/blob/master/containers/CMakeLists.txt#L16

What I have done is this: https://github.com/ED6E0F17/userland/commit/cc3eb42f10ee3603649e586e1b196c1ae10f8a2e

[popcornmix]

@fordfrog does @ED6E0F17's commit work for you? If so, I'm happy to include a change like that.

[ED6E0F17]

I need to abandon that patch. Cmake is not always used to build the applications in HelloPi, so it is necessary to keep the local definitions of _GNU_SOURCE there.

[fordfrog]

@popcornmix, @ED6E0F17: the patch works fine when building using cmake.

i will use it untill a more general solution is found. thank you.

[luked99]

I think it might be possible to just remove the function that calls sbrk().

e.g.

https://github.com/luked99/userland-1/commit/627eaebe50a26e28be365aca03efb932a25228cf

[ED6E0F17]

@luked99 : Didn`t you already fix this by sneaking a -D_GNU_SOURCE into your last pull request ?

[luked99]

That pull request got abandoned in the end. I think just removing the code seems better. It was originally (IIRC) for the benefit of VideoCore test harnesses that wanted to check for memory leaks. But trying to do so that way just seems very optimistic (the VideoCore version of the same function is fine). Better to use Valgrind, and better to remove a function that is ill-defined and likely to confuse at best.

(In my opinion, obviously; feel free to disagree :-)

[JamesH65]

After @luked99 merge last year, has this issue gone away? Seems related to #188

[JamesH65]

I believe this has been fixed.

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[aperezdc]

FWIW, there is a related problem (missing definition of _GNU_SOURCE) for the calls to clock_gettime() which use the CLOCK_* macros. Code that uses them is present in vcos_platform.h, see https://github.com/Igalia/buildroot-wpe/pull/2#discussion_r224958314

My impression is that in general the headers assume that the compiler will be using -std=gnu<something> (for example -std=gnu99) and when a program is built with a plain -std=c<something> (like -std=c99) the compiler will complain.

There are two solutions I can think of: One is removing the usage of clock_gettime() from the header and put it into a .c file which gets built with the needed preprocessor symbol(s) defined; and the other is adding -D_GNU_SOURCE to the compiler flags listed in bcm_host.pc.in. The first option seems better to me, because it does not force every program which uses the userland drivers to be compiled with _GNU_SOURCE defined (and many may not need it, or even not build with it defined!).