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When generating notoc call and branch stubs without the benefit of pc-relative insns, the stubs need to use LR to access the run time PC. All LR changes must be described in .eh_frame if we're to support unwinding through asynchronous exceptions. That's what this patch does. The patch has gone through way too many iterations. At first I attempted to add multiple FDEs, one for each stub. That ran into difficulties with do_plt_fde_location which is only capable of setting the address of a single FDE per Output_data section, and with removing any FDEs added on a previous do_relax pass. Removing FDEs (git commit be897fb774) went overboard in matching the FDE contents. That means either stashing the contents created for add_eh_frame_for_plt to use when calling remove_eh_frame_for_plt, or recreating contents on the fly (*) just to remove FDEs. In fact, FDE content matching is quite unnecesary. FDEs added by a previous do_relax pass are those with u_.from_linker.post_map set. So they can easily be recognised just by looking at that flag. This patch keeps that part of the multiple FDE changes. In the end I went for just one FDE per stub group to describe the call stubs. That's reasonably efficient for the common case of only needing to describe the __tls_get_addr_opt call stub. We don't expect to be making many calls using notoc stubs without pc-relative insns. *) Which has it's own set of problems. The contents must be recreated using the old stub layout, but .eh_frame size can affect stub requirements so you need to temporarily keep the old .eh_frame size when creating new stubs, then reset .eh_frame size before adding new FDEs. * ehframe.cc (Fde::operator==): Delete. (Cie::remove_fde): Delete. (Eh_frame::remove_ehframe_for_plt): Delete fde_data and fde_length parameters. Remove all post-map plt FDEs. * ehframe.h (Fde:post_map): Make const, add variant to compare plt. (Fde::operator==): Delete. (Cie::remove_fde): Implement here. (Cie::last_fde): New accessor. (Eh_frame::remove_ehframe_for_plt): Update prototype. * layout.cc (Layout::remove_eh_frame_for_plt): Delete fde_data and fde_length parameters. * layout.h (Layout::remove_eh_frame_for_plt): Update prototype. * powerpc.cc (Stub_table::tls_get_addr_opt_bctrl_): Delete. (Stub_table::plt_fde_len_, plt_fde_, init_plt_fde): Delete. (Stub_table::add_plt_call_entry): Don't set tls_get_addr_opt_bctrl_. (eh_advance): New function. (stub_sort): New function. (Stub_table::add_eh_frame): Emit eh_frame for notoc plt calls and branches as well as __tls_get_addr_opt plt call stub. (Stub_table::remove_eh_frame): Update to suit.
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