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