Messages in this thread | | | From | Nick Desaulniers <> | Date | Fri, 15 Mar 2019 14:31:09 -0700 | Subject | Re: [PATCH] x86/vdso: include generic __lshrdi3 in 32-bit vDSO |
| |
On Fri, Mar 15, 2019 at 12:54 PM 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.
__lshrdi3 is used for "logical shift right double-word by int" (best guess), so anywhere there's a right shift of a u64. Looks like there's a few of these in arch/x86/entry/vdso/, so it's legal for the compiler to emit this libcall. Do you know which function specifically in the .so has a relocation referencing __lshrdi3 specifically?
Is there a config I can set to reproduce this, in order to help test?
> > Signed-off-by: Matthias Kaehlcke <mka@chromium.org> > --- > arch/x86/entry/vdso/Makefile | 7 ++++++- > lib/lshrdi3.c | 4 +++- > 2 files changed, 9 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile > index 5bfe2243a08f..7517cd87e10b 100644 > --- a/arch/x86/entry/vdso/Makefile > +++ b/arch/x86/entry/vdso/Makefile > @@ -144,6 +144,7 @@ KBUILD_CFLAGS_32 += $(call cc-option, -fno-stack-protector) > KBUILD_CFLAGS_32 += $(call cc-option, -foptimize-sibling-calls) > KBUILD_CFLAGS_32 += -fno-omit-frame-pointer > KBUILD_CFLAGS_32 += -DDISABLE_BRANCH_PROFILING > +KBUILD_CFLAGS_32 += -DBUILD_VDSO > > ifdef CONFIG_RETPOLINE > ifneq ($(RETPOLINE_VDSO_CFLAGS),) > @@ -153,12 +154,16 @@ endif > > $(obj)/vdso32.so.dbg: KBUILD_CFLAGS = $(KBUILD_CFLAGS_32) > > +$(obj)/vdso32/lshrdi3.o: $(srctree)/lib/lshrdi3.c FORCE > + $(call if_changed_rule,cc_o_c)
+ Masahiro to help look at this part (I don't understand this part of kbuild).
> + > $(obj)/vdso32.so.dbg: FORCE \ > $(obj)/vdso32/vdso32.lds \ > $(obj)/vdso32/vclock_gettime.o \ > $(obj)/vdso32/note.o \ > $(obj)/vdso32/system_call.o \ > - $(obj)/vdso32/sigreturn.o > + $(obj)/vdso32/sigreturn.o \ > + $(obj)/vdso32/lshrdi3.o > $(call if_changed,vdso) > > # > 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>
Is this a simple cleanup, or?
> #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 > -- > 2.21.0.360.g471c308f928-goog
Compilers (GCC and Clang) will always assume their runtime has these helper functions; whether or not they emit libcalls vs inline routines is implementation defined. So I agree with this patch; I just would like to help confirm/test it. -- Thanks, ~Nick Desaulniers
| |