* Alan Modra: > On Mon, Sep 23, 2019 at 09:42:52AM +0200, Florian Weimer wrote: >> At Cauldron, the question came up whether the dynamic loader needs to >> be taught about the new relocations for PC-relative addressing. >> >> I think they would only matter if we supported PC-relative addressing >> *and* text relocations. Is that really necessary? >> >> These text relocations would not work reliably anyway because the >> maximum displacement is not large enough. For example, with the >> current process layout, it's impossible to reach shared objects from >> the main program and vice versa. And some systems might want to add >> additional randomization, so that shared objects are not mapped closed >> together anymore. > > We've been discussing this inside IBM too. The conclusion is that > only one of the new relocs makes any possible sense as a dynamic > reloc, R_PPC64_TPREL34, and that one only if you allow > -ftls-model=local-exec when building shared libraries and accept that > DF_STATIC_TLS shared libraries that can't be dlopen'd are OK.
Is this still a text relocation? The displacement relative to the thread pointer is (usually) small, so I can see how this could work reliable. What's the restriction on dlopen? Wouldn't it be the same as regular initial-exec TLS memory, which also uses static TLS, but without a text relocation and an additional indirection to load the TLS offset from a place where a regular relocation has put it?
