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

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On Thu, 2020-01-23 at 17:23 -0500, Steve Grubb wrote:
> On Tuesday, January 21, 2020 1:52:54 PM EST Jeff Law wrote:
> > > > > That was the idea.   Provide a trivial opt-out so that upstreams had
> > > > > time to fix properly.  I even volunteered to add the opt-out marker
> > > > > where appropriate to minimize the FTBFS issues.  I also volunteered
> > > > > to help with the packages that don't honor flags injection.
> > > > 
> > > > This sounds reasonable to me.
> > > > 
> > > > The PR is
> > > > https://src.fedoraproject.org/rpms/redhat-rpm-config/pull-request/77
> > > > 
> > > > I have reopened it.
> > > > 
> > > > The mass rebuild will notify the maintainrs and they can use that macro
> > > > to short-workaround the problem. It' also easier to grep from the specs
> > > > than custom patches and whatnots
> > > 
> > > I need something like this for suricata. It has about 45 variables
> > > causing this. And it's not a simple "extern" addition because it looks
> > > like in many cases the variable was never placed in a C file. Simply
> > > adding extern keyword leads undefined reference errors. This will take a
> > > while to sort out with upstream.
> > 
> > You also have to be careful if you're building shared libraries -- I
> > was looking at a package (I forget which) which built multiple DSOs.
> > If you're not careful you can end up with some DSOs which wouldn't have
> > the definition -- worse yet, you're not going to get an undefined
> > symbol when you build those DSOs.
> 
> So, I have a weird one. I'm compiling audit and getting multiple definitions.
> 
> I have
> 
> /usr/bin/ld: ausearch-checkpt.o:/home/sgrubb/working/BUILD/audit-3.0/src/
> ausearch-common.h:53: multiple definition of `event_node_list'; ausearch.o:/
> home/sgrubb/working/BUILD/audit-3.0/src/ausearch-common.h:53: first defined 
> here
> 
> $ cat ausearch-checkpt.c | grep event_node_list
> 
> Hmm. Nothing found.
> 
> $ objdump --syms ausearch-checkpt.o | grep event_node_list
> 0000000000000040 g     O .bss	0000000000000008 event_node_list
> 
> It's in the object file? In ausearch-checkpt.c we have #include "ausearch-
> checkpt.h which does not define it. That file has #include "ausearch-llist.h" 
> which does not define it. That file has #include "ausearch-common.h" which does 
> define it as:
> 
> extern slist *event_node_list;
> 
> So, what appears to be happening is all these C files are creating a definition 
> based on this and they don't even use this variable. It seems like they would 
> create a spot in their table *if and only if* it was referenced somewhere in 
> the code.  I'm not sure if this was intended but it will be a big problem for 
> everyone.
Use -save-temps and post the .i file.

An "extern blah blah blah" should not be doing that.

jeff
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