I have bee trying to prepare new patch to add libvdso support needed by golang based on the work of @benoit. I came across this discussion here https://groups.google.com/forum/#!searchin/osv-dev/Delay$20elf$20object$20initialization%7Csort:date/osv-dev/DOJ23sMsZuY/EgryjmqqCQAJ (look for "vdso fast syscall compatibility library" subthread).
The original patch prepared by Benoit add libvdso as a separate shared library whose base address gets passed to auxv as needed by Golang. Nadav argued in this thread that instead libvdso could be part of kernel and kernel base can be used instead (unless I misunderstood the conversation). To have better understanding I captured the based address of kernel by adding debug statement like so in application::prepare_argv() - https://github.com/benoit-canet/osv/blob/go4/core/app.cc#L298-L359: debug("***$$$$$ lbbvdso address: %#x\n", _libvdso->base()); auto _libxenstore = program->get_library("libxenstore.so.3.0"); if( _libxenstore) { debug("***$$$$$ libxenstore address: %#x\n", _libxenstore->base()); } libxenstore.so.3.0 is one of the "virtual" libraries that is resolvable as part of kernel (look at supplied_modules in program constructor). So if we added libvdso.so same way as libxenstore.so.3.0 we would pass its base address to auxv. Here is the output I am getting: ***$$$$$ lbbvdso address: 0x100000000000 ***$$$$$ libxenstore address: 0 For whatever reason the base address of any library provided by OSv kernel would be 0. Do we know why base address returned here is 0 instead of expected 0x200000? Here is the Golang portion of code with the guard that Benoit is referring - https://github.com/golang/go/blob/master/src/runtime/vdso_linux.go#L269-L273 case _AT_SYSINFO_EHDR: if val == 0 { // Something went wrong return } So clearly we cannot pass 0 as base address? So I wonder of there is some bug where base address of supplied modules is returned as 0 or indeed it is zero instead of 0x200000 and then the only choice we have is to have it a separate library. Am I missing something? Waldek -- You received this message because you are subscribed to the Google Groups "OSv Development" group. To unsubscribe from this group and stop receiving emails from it, send an email to osv-dev+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
