Hi! On Fri, Jan 10, 2020 at 09:50:48PM +0530, Siddhesh Poyarekar wrote: > Statically built independent programs that implement their own program > entry points (i.e. -ffreestanding -nostartfiles) and call __builtin_* > functions break when the builtin function in question is implemented as > an IFUNC in glibc and the builtin results in a glibc call instead of > some inline code. > > This happens because the startup code where ifuncs are resolved never > gets executed (since glibc's startup code is never executed) and hence > the PLT jumps fail. The bug report talks about this as an aarch64 > problem but I've been able to reproduce the problem on x86_64 as well. > One just needs to make sure that the __builtin_foo call results in a > glibc call.
-ffreestanding means you might not have any of the C standard library, and -nostartfiles means you do not do any of the standard initialisation. Why then would you expect any ifunc to work? > I spent some time thinking about this and while it's trivial to fix by > disabling ifuncs for static glibc, I wanted a solution that wasn't such > a big hammer. The other alternative I could think of is to have an > exported alias (called __builtin_strlen for example instead of strlen) > of a default implementation of the builtin function in glibc that gcc > generates a call to if freestanding && nostartfiles && static. > > Any thoughts or other ideas on how this could be implemented? Why do you not want the startfiles, but do want their effects? Segher
