[PATCH v6 0/6] ARM: vdso gettimeofday using generic timer architecture

[Russell King - ARM Linux]

On Tue, Apr 22, 2014 at 07:48:51PM -0500, Nathan Lynch wrote:
> - Build vdso.so with -lgcc: calls to __lshrdi3, __divsi3 sometimes
>   emitted (especially with -Os).  Override certain libgcc functions to
>   prevent undefined symbols.

This rather worries me.

For a start, the toolchain I use for cross-building kernels (which I
build myself from gnu.org source) never has a libgcc with it - that's
because in order to build libgcc, I need a libc, and I don't want to
have a full cross environment on my machine just to build the soddin
compiler.

So, I want to be able to build kernels without having a libgcc sitting
around.

Second point here is that we have multiple different versions of
userspace crap with multiple different ABIs.  Think about armel vs
armhf for starters.  There's at least *three* different ELF formats -
OABI, EABI armel, EABI armhf.  Okay, we can forget about OABI, but
what about the other two?  What about single zImage where you may
want a single kernel image which can run on either flavour?

It is not possible to build a single .so which is compatible with
both - an armhf dynamic linker rejects armel outright, and vice versa.

This, to me, sounds like one big fail... and as far as I'm aware, the
kernel has no idea itself which flavour of userspace is running, so it
has no idea which flavour of VDSO to offer (if it even had both.)

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