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Re: [PATCH 1/1] gold: Avoid duplicate PLT stub symbols on PowerPC

On Mon, Jun 19, 2017 at 12:34:42PM +0930, Alan Modra wrote:
> On Sun, Jun 18, 2017 at 10:58:03PM +0100, James Clarke wrote:
> > If two objects are compiled with -fPIC or -fPIE and call the same
> > function, two different PLT entries are created, one for each object,
> I'd be surprised if that was so when using your simple testcase, and
> testing here verifies it.  There is a situation where this can occur:
> In a very large binary it may be necessary to create multiple stubs to
> call a given function, because calls are so far apart that a single
> stub cannot be reached by a "bl" instruction.  However, that case
> ought to be covered by this->uniq_ being different for each
> stub_table.  So I'm not sure how you are getting the failure.

Incidentally, you can provoke multiple stubs with the small testcase
by using a ridiculously small --stub-group-size=64 (and ignore all the
warnings about section "exceeds group size".  If I do that, I see

nm printf | grep puts
0000000000000840 t 00000004.plt_call.puts
00000000000008a0 t 00000005.plt_call.puts
                 U puts

objdump also shows the two plt call stubs for puts.

> > but the same stub symbol name is used for both. Therefore let's make
> > the names unique by incorporating the object's uniq_ value where
> > necessary.
> > 
> > gold/
> > 	* (Stub_table::define_stub_syms): Include object's uniq_ value
> > 	when set for non-local symbols as well.
> This won't work.  object_ isn't set for ppc64 globals.  See the
> Plt_stub_ent constructors.

Alan Modra
Australia Development Lab, IBM

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