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 <[email protected]>
---
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)
+
$(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>
#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
On Fri, Mar 15, 2019 at 12:54 PM Matthias Kaehlcke <[email protected]> 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 <[email protected]>
> ---
> 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
Hi Nick,
On Fri, Mar 15, 2019 at 02:31:09PM -0700, 'Nick Desaulniers' via Clang Built Linux wrote:
> On Fri, Mar 15, 2019 at 12:54 PM Matthias Kaehlcke <[email protected]> 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?
It's the right shifts in do_realtime() and do_monotonic().
> Is there a config I can set to reproduce this, in order to help
> test?
I encountered it with a Chrome OS specific configuration, but a
defconfig should do. Note that you probably need a development version
of clang to reproduce this.
> >
> > Signed-off-by: Matthias Kaehlcke <[email protected]>
> > ---
> > 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).
I bluntly stole that from arch/x86/purgatory/Makefile , which does
something similar.
>
> > +
> > $(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?
The vDSO build is unhappy when modules.h draws in a whole bunch of
other kernel headers and export.h is all that's need. It seemed
reasonable to do the 'cleanup' in this patch since we touch it anyway
to place EXPORT_SYMBOL within an #ifdef.
> > #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
>
> 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 for your help!
Matthias
On March 15, 2019 3:29:06 PM PDT, Matthias Kaehlcke <[email protected]> wrote:
>Hi Nick,
>
>On Fri, Mar 15, 2019 at 02:31:09PM -0700, 'Nick Desaulniers' via Clang
>Built Linux wrote:
>> On Fri, Mar 15, 2019 at 12:54 PM Matthias Kaehlcke <[email protected]>
>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?
>
>It's the right shifts in do_realtime() and do_monotonic().
>
>> Is there a config I can set to reproduce this, in order to help
>> test?
>
>I encountered it with a Chrome OS specific configuration, but a
>defconfig should do. Note that you probably need a development version
>of clang to reproduce this.
>
>> >
>> > Signed-off-by: Matthias Kaehlcke <[email protected]>
>> > ---
>> > 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).
>
>I bluntly stole that from arch/x86/purgatory/Makefile , which does
>something similar.
>
>>
>> > +
>> > $(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?
>
>The vDSO build is unhappy when modules.h draws in a whole bunch of
>other kernel headers and export.h is all that's need. It seemed
>reasonable to do the 'cleanup' in this patch since we touch it anyway
>to place EXPORT_SYMBOL within an #ifdef.
>
>> > #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
>>
>> 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 for your help!
>
>Matthias
Note: it is also probably no reason to use -Os/-Oz for the vdso.
--
Sent from my Android device with K-9 Mail. Please excuse my brevity.
On Fri, Mar 15, 2019 at 04:18:31PM -0700, [email protected] wrote:
> Note: it is also probably no reason to use -Os/-Oz for the vdso.
Is anyone actually using -Os and CONFIG_CC_OPTIMIZE_FOR_SIZE ? I've been
staring at compiler output a lot lately and -Os really generates
atrocious crap.
That is, should we just get rid of it?
On Fri, Mar 15, 2019 at 3:29 PM Matthias Kaehlcke <[email protected]> wrote:
> On Fri, Mar 15, 2019 at 02:31:09PM -0700, 'Nick Desaulniers' via Clang Built Linux wrote:
> > Is there a config I can set to reproduce this, in order to help
> > test?
>
> I encountered it with a Chrome OS specific configuration, but a
> defconfig should do.
defconfig selects CONFIG_OPTIMIZE_FOR_PERFORMANCE=y. I needed to
select CONFIG_CC_OPTIMIZE_FOR_SIZE=y to repro. My CI is simply
running defconfigs, which is why I didn't catch this.
> Note that you probably need a development version
> of clang to reproduce this.
Yep. Thanks for the patch.
Tested-by: Nick Desaulniers <[email protected]>
--
Thanks,
~Nick Desaulniers
On Mon, Mar 18, 2019 at 10:09:37AM -0700, Nick Desaulniers wrote:
> On Fri, Mar 15, 2019 at 3:29 PM Matthias Kaehlcke <[email protected]> wrote:
> > On Fri, Mar 15, 2019 at 02:31:09PM -0700, 'Nick Desaulniers' via Clang Built Linux wrote:
> > > Is there a config I can set to reproduce this, in order to help
> > > test?
> >
> > I encountered it with a Chrome OS specific configuration, but a
> > defconfig should do.
>
> defconfig selects CONFIG_OPTIMIZE_FOR_PERFORMANCE=y. I needed to
> select CONFIG_CC_OPTIMIZE_FOR_SIZE=y to repro. My CI is simply
> running defconfigs, which is why I didn't catch this.
I suspect the right fix is to make clang use -Os and abolish that -Oz
madness.
Hi Peter,
On Mon, Mar 18, 2019 at 06:16:04PM +0100, Peter Zijlstra wrote:
> On Mon, Mar 18, 2019 at 10:09:37AM -0700, Nick Desaulniers wrote:
> > On Fri, Mar 15, 2019 at 3:29 PM Matthias Kaehlcke <[email protected]> wrote:
> > > On Fri, Mar 15, 2019 at 02:31:09PM -0700, 'Nick Desaulniers' via Clang Built Linux wrote:
> > > > Is there a config I can set to reproduce this, in order to help
> > > > test?
> > >
> > > I encountered it with a Chrome OS specific configuration, but a
> > > defconfig should do.
> >
> > defconfig selects CONFIG_OPTIMIZE_FOR_PERFORMANCE=y. I needed to
> > select CONFIG_CC_OPTIMIZE_FOR_SIZE=y to repro. My CI is simply
> > running defconfigs, which is why I didn't catch this.
>
> I suspect the right fix is to make clang use -Os and abolish that -Oz
> madness.
You have a point, enabling -Oz (aggressive optimization for size)
doesn't seem a good choice for the entire kernel.
I'll send a patch to change it (back) to -Os.
Matthias
On Mon, Mar 18, 2019 at 01:44:35PM -0700, Matthias Kaehlcke wrote:
> You have a point, enabling -Oz (aggressive optimization for size)
> doesn't seem a good choice for the entire kernel.
Note that in this instance, -Os actually generates _smaller_ code than
-Oz, now that's mostly because of stupid register shuffling, but still.
> I'll send a patch to change it (back) to -Os.
Thanks!
On Sat, Mar 16, 2019 at 4:55 AM Matthias Kaehlcke <[email protected]> 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 <[email protected]>
> ---
> 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/
I do not know if this patch is still needed.
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.
--
Best Regards
Masahiro Yamada
On Sat, Mar 16, 2019 at 6:32 AM Nick Desaulniers
<[email protected]> wrote:
>
> On Fri, Mar 15, 2019 at 12:54 PM Matthias Kaehlcke <[email protected]> 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 <[email protected]>
> > ---
> > 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
On Wed, Mar 20, 2019 at 10:55:06PM +0900, Masahiro Yamada wrote:
> On Sat, Mar 16, 2019 at 4:55 AM Matthias Kaehlcke <[email protected]> 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 <[email protected]>
> > ---
> > 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!