Re: [PATCH] x86/vdso: include generic __lshrdi3 in 32-bit vDSO

[Matthias Kaehlcke <mka@chromium.org>]

On Wed, Mar 20, 2019 at 10:55:06PM +0900, Masahiro Yamada wrote:
> On Sat, Mar 16, 2019 at 4:55 AM Matthias Kaehlcke <mka@chromium.org> wrote:
> >
> > Building the 32-bit vDSO with a recent clang version fails due
> > to undefined symbols:
> >
> > arch/x86/entry/vdso/vdso32.so.dbg: undefined symbols found
> >
> > The undefined symbol in this case is __lshrdi3, which is part of
> > the compiler runtime library, however the vDSO isn't linked against
> > this library.
> >
> > Include the kernel version of __lshrdi3 in the 32-bit vDSO build.
> >
> > Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
> > ---
> > diff --git a/lib/lshrdi3.c b/lib/lshrdi3.c
> > index 99cfa5721f2d..8a4fc6bcf3a4 100644
> > --- a/lib/lshrdi3.c
> > +++ b/lib/lshrdi3.c
> > @@ -16,7 +16,7 @@
> >   * to the Free Software Foundation, Inc.
> >   */
> >
> > -#include <linux/module.h>
> > +#include <linux/export.h>
> >  #include <linux/libgcc.h>
> >
> >  long long notrace __lshrdi3(long long u, word_type b)
> > @@ -42,4 +42,6 @@ long long notrace __lshrdi3(long long u, word_type b)
> >
> >         return w.ll;
> >  }
> > +#ifndef BUILD_VDSO
> >  EXPORT_SYMBOL(__lshrdi3);
> > +#endif
> 
> 
> I picked up
> https://patchwork.kernel.org/patch/10858565/

Great, thanks!

> I do not know if this patch is still needed.

no, with the change to -Os the patch isn't needed anymore.

> FYI, just a tip to turn EXPORT_SYMBOL into no-op cleanly.
> 
> You can use __DISABLE_EXPORTS
> as drivers/firmware/efi/libstub/Makefile does.
> 
> See commit f922c4abdf76.

Good to know, thanks for the pointer!