Messages in this thread | | | From | Masahiro Yamada <> | Date | Wed, 20 Mar 2019 23:06:20 +0900 | Subject | Re: [PATCH] x86/vdso: include generic __lshrdi3 in 32-bit vDSO |
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On Sat, Mar 16, 2019 at 6:32 AM Nick Desaulniers <ndesaulniers@google.com> wrote: > > 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).
This is a copy from scripts/Makefile.build, which is globally used to compile %.c -> %.o
-- Best Regards Masahiro Yamada
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