[PATCH] lib: Add shared copy of __lshrti3 from libgcc

Matthias Kaehlcke
2019-03-15T20:54:54Z

The compiler may emit calls to __lshrti3 from the compiler runtime
library, which results in undefined references:

arch/x86/kvm/x86.o: In function `mul_u64_u64_shr':
include/linux/math64.h:186: undefined reference to `__lshrti3'

Add a copy of the __lshrti3 libgcc routine (from gcc v4.9.2).

Include the function for x86 builds with clang, which is the
environment where the above error was observed.

Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
---
arch/x86/Kconfig | 1 +
include/linux/libgcc.h | 16 ++++++++++++++++
lib/Kconfig | 3 +++
lib/Makefile | 1 +
lib/lshrti3.c | 31 +++++++++++++++++++++++++++++++
5 files changed, 52 insertions(+)
create mode 100644 lib/lshrti3.c

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index c1f9b3cf437c..a5e0d923845d 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -105,6 +105,7 @@ config X86
select GENERIC_IRQ_PROBE
select GENERIC_IRQ_RESERVATION_MODE
select GENERIC_IRQ_SHOW
+ select GENERIC_LIB_LSHRTI3 if CC_IS_CLANG
select GENERIC_PENDING_IRQ if SMP
select GENERIC_SMP_IDLE_THREAD
select GENERIC_STRNCPY_FROM_USER
diff --git a/include/linux/libgcc.h b/include/linux/libgcc.h
index 32e1e0f4b2d0..a71036471838 100644
--- a/include/linux/libgcc.h
+++ b/include/linux/libgcc.h
@@ -22,15 +22,26 @@
#include <asm/byteorder.h>

typedef int word_type __attribute__ ((mode (__word__)));
+typedef int TItype __attribute__ ((mode (TI)));

#ifdef __BIG_ENDIAN
struct DWstruct {
int high, low;
};
+
+struct DWstruct128 {
+ long long high, low;
+};
+
#elif defined(__LITTLE_ENDIAN)
struct DWstruct {
int low, high;
};
+
+struct DWstruct128 {
+ long long low, high;
+};
+
#else
#error I feel sick.
#endif
@@ -40,4 +51,9 @@ typedef union {
long long ll;
} DWunion;

+typedef union {
+ struct DWstruct128 s;
+ TItype ll;
+} DWunion128;
+
#endif /* __ASM_LIBGCC_H */
diff --git a/lib/Kconfig b/lib/Kconfig
index a9e56539bd11..369e10259ea6 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -624,6 +624,9 @@ config GENERIC_LIB_ASHRDI3
config GENERIC_LIB_LSHRDI3
bool

+config GENERIC_LIB_LSHRTI3
+ bool
+
config GENERIC_LIB_MULDI3
bool

diff --git a/lib/Makefile b/lib/Makefile
index 4e066120a0d6..42648411f451 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -277,6 +277,7 @@ obj-$(CONFIG_PARMAN) += parman.o
obj-$(CONFIG_GENERIC_LIB_ASHLDI3) += ashldi3.o
obj-$(CONFIG_GENERIC_LIB_ASHRDI3) += ashrdi3.o
obj-$(CONFIG_GENERIC_LIB_LSHRDI3) += lshrdi3.o
+obj-$(CONFIG_GENERIC_LIB_LSHRTI3) += lshrti3.o
obj-$(CONFIG_GENERIC_LIB_MULDI3) += muldi3.o
obj-$(CONFIG_GENERIC_LIB_CMPDI2) += cmpdi2.o
obj-$(CONFIG_GENERIC_LIB_UCMPDI2) += ucmpdi2.o
diff --git a/lib/lshrti3.c b/lib/lshrti3.c
new file mode 100644
index 000000000000..2d2123bb3030
--- /dev/null
+++ b/lib/lshrti3.c
@@ -0,0 +1,31 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/export.h>
+#include <linux/libgcc.h>
+
+long long __lshrti3(long long u, word_type b)
+{
+ DWunion128 uu, w;
+ word_type bm;
+
+ if (b == 0)
+ return u;
+
+ uu.ll = u;
+ bm = 64 - b;
+
+ if (bm <= 0) {
+ w.s.high = 0;
+ w.s.low = (unsigned long long) uu.s.high >> -bm;
+ } else {
+ const unsigned long long carries =
+ (unsigned long long) uu.s.high << bm;
+ w.s.high = (unsigned long long) uu.s.high >> b;
+ w.s.low = ((unsigned long long) uu.s.low >> b) | carries;
+ }
+
+ return w.ll;
+}
+#ifndef BUILD_VDSO
+EXPORT_SYMBOL(__lshrti3);
+#endif
--
2.21.0.360.g471c308f928-goog