Re: gcc 10: Default to -fno-common, multiple definitions of ...

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On Wed, Jan 22, 2020 at 5:42 AM Miro Hrončok <mhroncok@xxxxxxxxxx> wrote:
>
> On 22. 01. 20 12:33, Fabio Valentini wrote:
> > On Wed, Jan 22, 2020 at 12:12 PM Kevin Kofler <kevin.kofler@xxxxxxxxx> wrote:
> >>
> >> Miro Hrončok wrote:
> >>> https://gcc.gnu.org/gcc-10/porting_to.html#common
> >>>
> >>> "Default to -fno-common
> >>>
> >>> A common mistake in C is omitting extern when declaring a global variable
> >>> in a header file. If the header is included by several files it results in
> >>> multiple definitions of the same variable. In previous GCC versions this
> >>> error is ignored. GCC 10 defaults to -fno-common, which means a linker
> >>> error will now be reported. To fix this, use extern in header files when
> >>> declaring global variables, and ensure each global is defined in exactly
> >>> one C file. As a workaround, legacy C code can be compiled with -fcommon.
> >>>
> >>>
> >>>         int x;  // tentative definition - avoid in header files
> >>>
> >>>         extern int y;  // correct declaration in a header file"
> >>
> >> I fail to see how this kind of incompatible change that breaks hundreds of
> >> packages (and certainly a lot more software out there) is an improvement.
> >>
> >>          Kevin Kofler
> >
> > Honestly, it would have been good to mention that GCC 10 contains such
> > a breaking change, either on the GCC10 Change proposal wiki page, or
> > in the FESCo ticket.
> > Neither was the case. :(
> >
> > Now we still don't have a publicly available list of broken packages
> > (which, apparently, was known?) - can we please get the list?
> > I don't care where, but adding a link to it to either the Change wiki
> > page or the FESCo ticket would be great, so we can better deal with
> > it.
>
> This is what I got offlist.
>
> "This was generated in early December.  There may be minor differences
> due to package updates, deprecations, etc.  But this should be  95%
> complete."
>
The list is certainly incomplete. Kernel and kernel-tools are not on
it, but don't build due to it.  And, the issues don't seem to be "due
to updates" rather code that has been there for quite some time.

Justin
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