On March 18, 2019 2:31:13 PM PDT, Matthias Kaehlcke <m...@chromium.org> wrote: >On Fri, Mar 15, 2019 at 01:54:50PM -0700, Matthias Kaehlcke 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' >> >> 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 <m...@chromium.org> > >With "Revert "kbuild: use -Oz instead of -Os when using clang" >(https://lore.kernel.org/patchwork/patch/1051932/) the above >error is fixed, a few comments inline for if the patch is >resurrected in the future because __lshrti3 is emitted in a >different context. > >> 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))); > >Consider using __int128 instead. Definition and use need a >'defined(__SIZEOF_INT128__)' guard (similar for mode (TI)), since >these 128 bit types aren't supported on all platforms. > >> #ifdef __BIG_ENDIAN >> struct DWstruct { >> int high, low; >> }; >> + >> +struct DWstruct128 { >> + long long high, low; >> +}; > >This struct isn't needed, struct DWstruct can be used. > >> 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) > >use TItype for input/output, which is what gcc does, though the above >matches the interface in the documentation. > >> +{ >> + 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; > >include <linux/types.h> and use u64 instead of unsigned long long.
Ok, now I'm really puzzled. How could we need a 128-bit shift when the prototype only has 64 bits of input?! -- Sent from my Android device with K-9 Mail. Please excuse my brevity.