On Fri, Mar 15, 2019 at 04:53:40PM -0700, h...@zytor.com wrote: > On March 15, 2019 4:47:01 PM PDT, Matthias Kaehlcke <m...@chromium.org> wrote: > >On Fri, Mar 15, 2019 at 03:12:08PM -0700, h...@zytor.com wrote: > >> On March 15, 2019 3:06:37 PM PDT, Nick Desaulniers > ><ndesaulni...@google.com> wrote: > >> >On Fri, Mar 15, 2019 at 1:54 PM Matthias Kaehlcke <m...@chromium.org> > >> >wrote: > >> >> > >> >> 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' > >> > > >> >Looks like Clang will emit this at -Oz (but not -O2): > >> >https://godbolt.org/z/w1_2YC > >> > > >> >> > >> >> Add a copy of the __lshrti3 libgcc routine (from gcc v4.9.2). > >> > > >> >Has it changed since? If so why not a newer version of libgcc_s? > >> > > >> >> > >> >> Include the function for x86 builds with clang, which is the > >> >> environment where the above error was observed. > >> >> > >> >> Signed-off-by: Matthias Kaehlcke <m...@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))); > >> > > >> >Well that's an interesting new compiler attribute. > >> > >>https://stackoverflow.com/questions/4559025/what-does-gcc-attribute-modexx-actually-do > >> >Please use `__mode(TI)` from include/linux/compiler_attributes.h ex. > >> >typedef int TItype __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 > >> > > >> >I don't think you want this. Maybe that was carried over from > >> >https://lkml.org/lkml/2019/3/15/669 > >> >by accident? The above linkage error mentions arch/x86/kvm/x86.o > >> >which I wouldn't expect to be linked into the VDSO image? > >> > >> Or just "u64"... > > > >Are you referring to TItype? It currenty is a 128-bit value. > > You're right, so "unsigned __int128"...
I liked the idea, however __int128 isn't supported by all platforms: include/linux/libgcc.h:57:11: error: __int128 is not supported on this target unsigned __int128 ll; That's from building the 32-bit VDSO for x86.