| Message ID | 20210512105440.748153-2-pbonzini@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | fix long division routines for ARM eabi | expand |
Hi Paolo, On 5/12/21 11:54 AM, Paolo Bonzini wrote: > Avoid possible uninitialized variables on machines where > division by zero does not trap. Add __divmoddi4, and > use it in __moddi3 and __divdi3. Looks good now, I like the change to __moddi3 and __divdi3 as that means that the tests will cover __divmoddi4, and the functions are now similar to their unsigned counterparts: Reviewed-by: Alexandru Elisei <alexandru.elisei@arm.com> Thanks, Alex > > Reported-by: Alexandru Elisei <alexandru.elisei@arm.com> > Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> > --- > lib/ldiv32.c | 40 ++++++++++++++++++++++++---------------- > 1 file changed, 24 insertions(+), 16 deletions(-) > > diff --git a/lib/ldiv32.c b/lib/ldiv32.c > index 96f4b35..897a4b9 100644 > --- a/lib/ldiv32.c > +++ b/lib/ldiv32.c > @@ -1,6 +1,7 @@ > #include <stdint.h> > > extern uint64_t __udivmoddi4(uint64_t num, uint64_t den, uint64_t *p_rem); > +extern int64_t __divmoddi4(int64_t num, int64_t den, int64_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); > @@ -11,8 +12,11 @@ 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) > + if (den == 0) { > + if (p_rem) > + *p_rem = 0; > return 1/((unsigned)den); > + } > > if (num >= den) { > /* Align den to num to avoid wasting time on leftmost zero bits. */ > @@ -35,31 +39,35 @@ uint64_t __udivmoddi4(uint64_t num, uint64_t den, uint64_t *p_rem) > return quot; > } > > -int64_t __moddi3(int64_t num, int64_t den) > +int64_t __divmoddi4(int64_t num, int64_t den, int64_t *p_rem) > { > - uint64_t mask = num < 0 ? -1 : 0; > + int32_t nmask = num < 0 ? -1 : 0; > + int32_t qmask = (num ^ den) < 0 ? -1 : 0; > + uint64_t quot; > > /* Compute absolute values and do an unsigned division. */ > - num = (num + mask) ^ mask; > + num = (num + nmask) ^ nmask; > if (den < 0) > den = -den; > > - /* Copy sign of num into result. */ > - return (__umoddi3(num, den) + mask) ^ mask; > + /* Copy sign of num^den into quotient, sign of num into remainder. */ > + quot = (__udivmoddi4(num, den, (uint64_t *)p_rem) + qmask) ^ qmask; > + if (p_rem) > + *p_rem = (*p_rem + nmask) ^ nmask; > + return quot; > } > > -int64_t __divdi3(int64_t num, int64_t den) > +int64_t __moddi3(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; > + int64_t rem; > + __divmoddi4(num, den, &rem); > + return rem; > +} > > - /* Copy sign of num^den into result. */ > - return (__udivdi3(num, den) + mask) ^ mask; > +int64_t __divdi3(int64_t num, int64_t den) > +{ > + int64_t rem; > + return __divmoddi4(num, den, &rem); > } > > uint64_t __udivdi3(uint64_t num, uint64_t den)
diff --git a/lib/ldiv32.c b/lib/ldiv32.c index 96f4b35..897a4b9 100644 --- a/lib/ldiv32.c +++ b/lib/ldiv32.c @@ -1,6 +1,7 @@ #include <stdint.h> extern uint64_t __udivmoddi4(uint64_t num, uint64_t den, uint64_t *p_rem); +extern int64_t __divmoddi4(int64_t num, int64_t den, int64_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); @@ -11,8 +12,11 @@ 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) + if (den == 0) { + if (p_rem) + *p_rem = 0; return 1/((unsigned)den); + } if (num >= den) { /* Align den to num to avoid wasting time on leftmost zero bits. */ @@ -35,31 +39,35 @@ uint64_t __udivmoddi4(uint64_t num, uint64_t den, uint64_t *p_rem) return quot; } -int64_t __moddi3(int64_t num, int64_t den) +int64_t __divmoddi4(int64_t num, int64_t den, int64_t *p_rem) { - uint64_t mask = num < 0 ? -1 : 0; + int32_t nmask = num < 0 ? -1 : 0; + int32_t qmask = (num ^ den) < 0 ? -1 : 0; + uint64_t quot; /* Compute absolute values and do an unsigned division. */ - num = (num + mask) ^ mask; + num = (num + nmask) ^ nmask; if (den < 0) den = -den; - /* Copy sign of num into result. */ - return (__umoddi3(num, den) + mask) ^ mask; + /* Copy sign of num^den into quotient, sign of num into remainder. */ + quot = (__udivmoddi4(num, den, (uint64_t *)p_rem) + qmask) ^ qmask; + if (p_rem) + *p_rem = (*p_rem + nmask) ^ nmask; + return quot; } -int64_t __divdi3(int64_t num, int64_t den) +int64_t __moddi3(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; + int64_t rem; + __divmoddi4(num, den, &rem); + return rem; +} - /* Copy sign of num^den into result. */ - return (__udivdi3(num, den) + mask) ^ mask; +int64_t __divdi3(int64_t num, int64_t den) +{ + int64_t rem; + return __divmoddi4(num, den, &rem); } uint64_t __udivdi3(uint64_t num, uint64_t den)
Avoid possible uninitialized variables on machines where division by zero does not trap. Add __divmoddi4, and use it in __moddi3 and __divdi3. Reported-by: Alexandru Elisei <alexandru.elisei@arm.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> --- lib/ldiv32.c | 40 ++++++++++++++++++++++++---------------- 1 file changed, 24 insertions(+), 16 deletions(-)