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"... -- Sent from my Android device with K-9 Mail. Please excuse my brevity.
