Messages in this thread | | | From | Nick Desaulniers <> | Date | Fri, 15 Mar 2019 15:06:37 -0700 | Subject | Re: [PATCH] lib: Add shared copy of __lshrti3 from libgcc |
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On Fri, Mar 15, 2019 at 1:54 PM Matthias Kaehlcke <mka@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 <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)));
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? -- Thanks, ~Nick Desaulniers
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