On Mon, Aug 17, 2015 at 10:29:41PM -0700, Cary Coutant wrote: > > So far, I've been prototyping static PIE support by having GCC pass > > the following options to ld instead of -static -pie: > > > > -static -shared -Bsymbolic > > > > This partly works, but since ld does not know it's producing a main > > executable, it misses important details, including the ability to link > > initial-exec and local-exec model TLS code correctly, as well as > > various linking optimizations. So I think the right way forward is > > making ld accept -static and -pie together to do the right thing. > > For the uses you have in mind, -static and -pie together make perfect > sense, but I'd argue that the output file in that case ought to be > ET_EXEC, since it will be in fact a standalone binary to be loaded > directly by the kernel. Not only would you want to omit the .interp > section (actually the PT_INTERP segment), but you also have no need > for the PT_DYNAMIC segment (.dynamic section).
As far as I can tell, on the kernel side ET_EXEC implies MAP_FIXED. Use of ET_EXEC vs ET_DYN is a separate matter from whether or not PT_DYNAMIC exists. Non-PIE dynamic-linked main executables with type ET_EXEC have PT_DYNAMIC, for example. > The only thing you need over a standard ET_EXEC file is the dynamic > relocations, with linker-generated symbols bracketing the start and > end of the relocations so that your custom startup code can find them. > It should be reasonably easy to arrange for these. Yes but it's much easier to use _DYNAMIC, and this is also more compatible with existing tools. I suspect gdb would have trouble if _DYNAMIC were missing, though I haven't checked. There's also the matter of arch-specific mess in _DYNAMIC (e.g. the wacky MIPS 'compacted' relocation table for the GOT) that would be a lot of arch-specific work to reimplement with an alternate scheme. bFLT already played the game of "let's redo relocation information in an ad-hoc way instead of using existing ELF mechanisms" and it was an utter mess; I don't want to go down that road again. Rich
