On Wed, May 5, 2021 at 6:16 AM Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
>
> On 05/05/21 15:14, Paolo Bonzini wrote:
> > The -nostdlib flag disables the driver from adding libclang_rt.*.a
> > during linking. Adding a specific library to the command line such as
> > libgcc then causes the linker to report unresolved symbols, because the
> > libraries that resolve those symbols aren't automatically added.
> >
> > libgcc however is only needed for long division (64-bit by 64-bit).
> > Instead of linking the whole of it, implement the routines that are
> > needed.
> >
> > Reported-by: Bill Wendling <morbo@xxxxxxxxxx>
> > Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
>
Thanks, Paolo!
-bw
> Oops, I didn't actually remove libgcc!
>
> diff --git a/Makefile b/Makefile
> index 24b7917..ddebcae 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -25,8 +25,6 @@ cc-option = $(shell if $(CC) -Werror $(1) -S -o /dev/null -xc /dev/null \
> #make sure env CFLAGS variable is not used
> CFLAGS =
>
> -libgcc := $(shell $(CC) --print-libgcc-file-name)
> -
> libcflat := lib/libcflat.a
> cflatobjs := \
> lib/argv.o \
> diff --git a/arm/Makefile.common b/arm/Makefile.common
> index 55478ec..38385e0 100644
> --- a/arm/Makefile.common
> +++ b/arm/Makefile.common
> @@ -58,9 +58,7 @@ OBJDIRS += lib/arm
> libeabi = lib/arm/libeabi.a
> eabiobjs = lib/arm/eabi_compat.o
>
> -libgcc := $(shell $(CC) $(machine) --print-libgcc-file-name)
> -
> -FLATLIBS = $(libcflat) $(LIBFDT_archive) $(libgcc) $(libeabi)
> +FLATLIBS = $(libcflat) $(LIBFDT_archive) $(libeabi)
> %.elf: LDFLAGS = -nostdlib $(arch_LDFLAGS)
> %.elf: %.o $(FLATLIBS) $(SRCDIR)/arm/flat.lds $(cstart.o)
> $(CC) $(CFLAGS) -c -o $(@:.elf=.aux.o) $(SRCDIR)/lib/auxinfo.c \
> diff --git a/x86/Makefile.common b/x86/Makefile.common
> index 55f7f28..52bb7aa 100644
> --- a/x86/Makefile.common
> +++ b/x86/Makefile.common
> @@ -37,12 +37,10 @@ COMMON_CFLAGS += -O1
> # stack.o relies on frame pointers.
> KEEP_FRAME_POINTER := y
>
> -libgcc := $(shell $(CC) -m$(bits) --print-libgcc-file-name)
> -
> # We want to keep intermediate file: %.elf and %.o
> .PRECIOUS: %.elf %.o
>
> -FLATLIBS = lib/libcflat.a $(libgcc)
> +FLATLIBS = lib/libcflat.a
> %.elf: %.o $(FLATLIBS) $(SRCDIR)/x86/flat.lds $(cstart.o)
> $(CC) $(CFLAGS) -nostdlib -o $@ -Wl,-T,$(SRCDIR)/x86/flat.lds \
> $(filter %.o, $^) $(FLATLIBS)
>
>
> > ---
> > arm/Makefile.arm | 1 +
> > lib/ldiv32.c | 105 ++++++++++++++++++++++++++++++++++++++++++++++
> > x86/Makefile.i386 | 2 +-
> > 3 files changed, 107 insertions(+), 1 deletion(-)
> > create mode 100644 lib/ldiv32.c
> >
> > diff --git a/arm/Makefile.arm b/arm/Makefile.arm
> > index d379a28..687a8ed 100644
> > --- a/arm/Makefile.arm
> > +++ b/arm/Makefile.arm
> > @@ -23,6 +23,7 @@ cstart.o = $(TEST_DIR)/cstart.o
> > cflatobjs += lib/arm/spinlock.o
> > cflatobjs += lib/arm/processor.o
> > cflatobjs += lib/arm/stack.o
> > +cflatobjs += lib/ldiv32.o
> >
> > # arm specific tests
> > tests =
> > diff --git a/lib/ldiv32.c b/lib/ldiv32.c
> > new file mode 100644
> > index 0000000..e9d434f
> > --- /dev/null
> > +++ b/lib/ldiv32.c
> > @@ -0,0 +1,105 @@
> > +#include <inttypes.h>
> > +
> > +extern uint64_t __udivmoddi4(uint64_t num, uint64_t den, uint64_t *p_rem);
> > +extern int64_t __moddi3(int64_t num, int64_t den);
> > +extern int64_t __divdi3(int64_t num, int64_t den);
> > +extern uint64_t __udivdi3(uint64_t num, uint64_t den);
> > +extern uint64_t __umoddi3(uint64_t num, uint64_t den);
> > +
> > +uint64_t __udivmoddi4(uint64_t num, uint64_t den, uint64_t *p_rem)
> > +{
> > + uint64_t quot = 0;
> > +
> > + /* Trigger a division by zero at run time (trick taken from iPXE). */
> > + if (den == 0)
> > + return 1/((unsigned)den);
> > +
> > + if (num >= den) {
> > + /* Align den to num to avoid wasting time on leftmost zero bits. */
> > + int n = __builtin_clzll(den) - __builtin_clzll(num);
> > + den <<= n;
> > +
> > + do {
> > + quot <<= 1;
> > + if (num >= den) {
> > + num -= den;
> > + quot |= 1;
> > + }
> > + den >>= 1;
> > + } while (n--);
> > + }
> > +
> > + if (p_rem)
> > + *p_rem = num;
> > +
> > + return quot;
> > +}
> > +
> > +int64_t __moddi3(int64_t num, int64_t den)
> > +{
> > + uint64_t mask = num < 0 ? -1 : 0;
> > +
> > + /* Compute absolute values and do an unsigned division. */
> > + num = (num + mask) ^ mask;
> > + if (den < 0)
> > + den = -den;
> > +
> > + /* Copy sign of num into result. */
> > + return (__umoddi3(num, den) + mask) ^ mask;
> > +}
> > +
> > +int64_t __divdi3(int64_t num, int64_t den)
> > +{
> > + uint64_t mask = (num ^ den) < 0 ? -1 : 0;
> > +
> > + /* Compute absolute values and do an unsigned division. */
> > + if (num < 0)
> > + num = -num;
> > + if (den < 0)
> > + den = -den;
> > +
> > + /* Copy sign of num^den into result. */
> > + return (__udivdi3(num, den) + mask) ^ mask;
> > +}
> > +
> > +uint64_t __udivdi3(uint64_t num, uint64_t den)
> > +{
> > + uint64_t rem;
> > + return __udivmoddi4(num, den, &rem);
> > +}
> > +
> > +uint64_t __umoddi3(uint64_t num, uint64_t den)
> > +{
> > + uint64_t rem;
> > + __udivmoddi4(num, den, &rem);
> > + return rem;
> > +}
> > +
> > +#ifdef TEST
> > +#include <assert.h>
> > +#define UTEST(a, b, q, r) assert(__udivdi3(a, b) == q && __umoddi3(a, b) == r)
> > +#define STEST(a, b, q, r) assert(__divdi3(a, b) == q && __moddi3(a, b) == r)
> > +int main()
> > +{
> > + UTEST(1, 1, 1, 0);
> > + UTEST(2, 2, 1, 0);
> > + UTEST(5, 3, 1, 2);
> > + UTEST(10, 3, 3, 1);
> > + UTEST(120, 3, 40, 0);
> > + UTEST(120, 1, 120, 0);
> > + UTEST(0x7FFFFFFFFFFFFFFFULL, 17, 0x787878787878787, 8);
> > + UTEST(0x7FFFFFFFFFFFFFFFULL, 0x787878787878787, 17, 8);
> > + UTEST(0x8000000000000001ULL, 17, 0x787878787878787, 10);
> > + UTEST(0x8000000000000001ULL, 0x787878787878787, 17, 10);
> > + UTEST(0, 5, 0, 0);
> > +
> > + STEST(0x7FFFFFFFFFFFFFFFULL, 17, 0x787878787878787, 8);
> > + STEST(0x7FFFFFFFFFFFFFFFULL, -17, -0x787878787878787, 8);
> > + STEST(-0x7FFFFFFFFFFFFFFFULL, 17, -0x787878787878787, -8);
> > + STEST(-0x7FFFFFFFFFFFFFFFULL, -17, 0x787878787878787, -8);
> > + STEST(33, 5, 6, 3);
> > + STEST(33, -5, -6, 3);
> > + STEST(-33, 5, -6, -3);
> > + STEST(-33, -5, 6, -3);
> > +}
> > +#endif
> > diff --git a/x86/Makefile.i386 b/x86/Makefile.i386
> > index c04e5aa..960e274 100644
> > --- a/x86/Makefile.i386
> > +++ b/x86/Makefile.i386
> > @@ -3,7 +3,7 @@ bits = 32
> > ldarch = elf32-i386
> > COMMON_CFLAGS += -mno-sse -mno-sse2
> >
> > -cflatobjs += lib/x86/setjmp32.o
> > +cflatobjs += lib/x86/setjmp32.o lib/ldiv32.o
> >
> > tests = $(TEST_DIR)/taskswitch.flat $(TEST_DIR)/taskswitch2.flat \
> > $(TEST_DIR)/cmpxchg8b.flat $(TEST_DIR)/la57.flat
> >
>
