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