On 2016-04-19 at 14:15 -0700, Cary Coutant wrote: > > > > > In theory, I think you could build a shared object that has an > > > entry > > > point so it could act as an executable, but you'd need to build > > > some > > > startup files that don't currently exist. For a binary to act as > > > an > > > executable, it needs an entry point, but the entry point is not > > > "main" > > > -- it's "_start", defined in crt1.o, which performs a bunch of > > > runtime > > > initialization before actually calling "main". The crt1.o that > > > comes > > > with your compiler probably has non-PIC code in it, so you can't > > > link > > > it into a shared library. > > > > Yes, indeed, but I'm not calling _start() from the loader, I'm > > calling > > main()... so I guess non-PIC-ness of the startup code does not > > matter, > > does it? > > Maybe I misunderstood your original question. Yes, you're calling the > payload's main() from your loader, and that's OK because your loader > has already started up through the crt startup code. But I thought > you > were trying to link the payload binary so that it could also serve as > an executable that could be launched by itself rather than via the > loader. To do that, you need the startup code in the crt*.o files, > and > that code will call your payload's main(). Yes, I understand. But what does *not* work is exactly "calling the payload's main() from the loader". On the other hand, starting the payload directly *does* work. Speaking more generally, how can presence/absence of non-PIC startup code (in the payload) influence the code path where that startup code is *not* used? -- Ivan Shapovalov / intelfx / > > > What else differs between -shared and -pie so that dlopen()'ing > > -shared > > executable works well with TLS, but dlopen()'ing -pie executable > > does > > not work? > > Off the top of my head, I can't think of anything, but I suspect > there's at least a 50% chance that there are other obstacles. > > -cary
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