* [PATCH kvm-unit-tests 0/2] fix long division routines for ARM eabi
@ 2021-05-11 17:41 Paolo Bonzini
2021-05-11 17:41 ` [PATCH kvm-unit-tests 1/2] libcflat: clean up and complete long division routines Paolo Bonzini
2021-05-11 17:41 ` [PATCH kvm-unit-tests 2/2] arm: add eabi version of 64-bit division functions Paolo Bonzini
0 siblings, 2 replies; 5+ messages in thread
From: Paolo Bonzini @ 2021-05-11 17:41 UTC (permalink / raw)
To: kvm; +Cc: Alexandru Elisei
As reported by Alexandru, ARM follows a different convention than
x86 so it needs __aeabi_ldivmod and __aeabi_uldivmod. Because
it does not use __divdi3 and __moddi3, it also needs __divmoddi4
to build the eabi function upon.
Paolo
Paolo Bonzini (2):
libcflat: clean up and complete long division routines
arm: add eabi version of 64-bit division functions
arm/Makefile.arm | 1 +
lib/arm/ldivmod.S | 32 ++++++++++++++++++++++++++++++++
lib/ldiv32.c | 28 +++++++++++++++++++++++++---
3 files changed, 58 insertions(+), 3 deletions(-)
create mode 100644 lib/arm/ldivmod.S
--
2.31.1
^ permalink raw reply [flat|nested] 5+ messages in thread
* [PATCH kvm-unit-tests 1/2] libcflat: clean up and complete long division routines
2021-05-11 17:41 [PATCH kvm-unit-tests 0/2] fix long division routines for ARM eabi Paolo Bonzini
@ 2021-05-11 17:41 ` Paolo Bonzini
2021-05-12 10:39 ` Alexandru Elisei
2021-05-11 17:41 ` [PATCH kvm-unit-tests 2/2] arm: add eabi version of 64-bit division functions Paolo Bonzini
1 sibling, 1 reply; 5+ messages in thread
From: Paolo Bonzini @ 2021-05-11 17:41 UTC (permalink / raw)
To: kvm; +Cc: Alexandru Elisei
Avoid possible uninitialized variables on machines where
division by zero does not trap. Add __divmoddi4, and
do not use 64-bit math unnecessarily in __moddi3 and __divdi3.
Reported-by: Alexandru Elisei <alexandru.elisei@arm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
lib/ldiv32.c | 28 +++++++++++++++++++++++++---
1 file changed, 25 insertions(+), 3 deletions(-)
diff --git a/lib/ldiv32.c b/lib/ldiv32.c
index 96f4b35..c39fccd 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. */
@@ -35,9 +39,27 @@ uint64_t __udivmoddi4(uint64_t num, uint64_t den, uint64_t *p_rem)
return quot;
}
+int64_t __divmoddi4(int64_t num, int64_t den, int64_t *p_rem)
+{
+ 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 + nmask) ^ nmask;
+ if (den < 0)
+ den = -den;
+
+ /* Copy sign of num^den into quotient, sign of num into remainder. */
+ quot = (__divmoddi4(num, den, p_rem) + qmask) ^ qmask;
+ if (p_rem)
+ *p_rem = (*p_rem + nmask) ^ nmask;
+ return quot;
+}
+
int64_t __moddi3(int64_t num, int64_t den)
{
- uint64_t mask = num < 0 ? -1 : 0;
+ int32_t mask = num < 0 ? -1 : 0;
/* Compute absolute values and do an unsigned division. */
num = (num + mask) ^ mask;
@@ -50,7 +72,7 @@ int64_t __moddi3(int64_t num, int64_t den)
int64_t __divdi3(int64_t num, int64_t den)
{
- uint64_t mask = (num ^ den) < 0 ? -1 : 0;
+ int32_t mask = (num ^ den) < 0 ? -1 : 0;
/* Compute absolute values and do an unsigned division. */
if (num < 0)
--
2.31.1
^ permalink raw reply related [flat|nested] 5+ messages in thread
* [PATCH kvm-unit-tests 2/2] arm: add eabi version of 64-bit division functions
2021-05-11 17:41 [PATCH kvm-unit-tests 0/2] fix long division routines for ARM eabi Paolo Bonzini
2021-05-11 17:41 ` [PATCH kvm-unit-tests 1/2] libcflat: clean up and complete long division routines Paolo Bonzini
@ 2021-05-11 17:41 ` Paolo Bonzini
1 sibling, 0 replies; 5+ messages in thread
From: Paolo Bonzini @ 2021-05-11 17:41 UTC (permalink / raw)
To: kvm; +Cc: Alexandru Elisei
eabi prescribes different entry points for 64-bit division on
32-bit platforms. Implement a wrapper for the GCC-style __divmoddi4
and __udivmoddi4 functions.
Reported-by: Alexandru Elisei <alexandru.elisei@arm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arm/Makefile.arm | 1 +
lib/arm/ldivmod.S | 32 ++++++++++++++++++++++++++++++++
2 files changed, 33 insertions(+)
create mode 100644 lib/arm/ldivmod.S
diff --git a/arm/Makefile.arm b/arm/Makefile.arm
index 687a8ed..3a4cc6b 100644
--- a/arm/Makefile.arm
+++ b/arm/Makefile.arm
@@ -24,6 +24,7 @@ cflatobjs += lib/arm/spinlock.o
cflatobjs += lib/arm/processor.o
cflatobjs += lib/arm/stack.o
cflatobjs += lib/ldiv32.o
+cflatobjs += lib/arm/ldivmod.o
# arm specific tests
tests =
diff --git a/lib/arm/ldivmod.S b/lib/arm/ldivmod.S
new file mode 100644
index 0000000..de11ac9
--- /dev/null
+++ b/lib/arm/ldivmod.S
@@ -0,0 +1,32 @@
+// EABI ldivmod and uldivmod implementation based on libcompiler-rt
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses.
+
+ .syntax unified
+ .align 2
+ .globl __aeabi_uldivmod
+ .type __aeabi_uldivmod, %function
+__aeabi_uldivmod:
+ push {r11, lr}
+ sub sp, sp, #16
+ add r12, sp, #8
+ str r12, [sp] // third argument to __udivmoddi4
+ bl __udivmoddi4
+ ldr r2, [sp, #8] // remainder returned in r2-r3
+ ldr r3, [sp, #12]
+ add sp, sp, #16
+ pop {r11, pc}
+
+ .globl __aeabi_ldivmod
+ .type __aeabi_ldivmod, %function
+__aeabi_ldivmod:
+ push {r11, lr}
+ sub sp, sp, #16
+ add r12, sp, #8
+ str r12, [sp] // third argument to __divmoddi4
+ bl __divmoddi4
+ ldr r2, [sp, #8] // remainder returned in r2-r3
+ ldr r3, [sp, #12]
+ add sp, sp, #16
+ pop {r11, pc}
--
2.31.1
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH kvm-unit-tests 1/2] libcflat: clean up and complete long division routines
2021-05-11 17:41 ` [PATCH kvm-unit-tests 1/2] libcflat: clean up and complete long division routines Paolo Bonzini
@ 2021-05-12 10:39 ` Alexandru Elisei
2021-05-12 10:47 ` Paolo Bonzini
0 siblings, 1 reply; 5+ messages in thread
From: Alexandru Elisei @ 2021-05-12 10:39 UTC (permalink / raw)
To: Paolo Bonzini, kvm
Hi Paolo,
Thanks for sending this so quickly!
On 5/11/21 6:41 PM, Paolo Bonzini wrote:
> Avoid possible uninitialized variables on machines where
> division by zero does not trap. Add __divmoddi4, and
According to the ARM Architecture Reference Manual for ARMv7-A (ARM DDI 0406C.d),
hardware floating point support is optional (page A2-54), so initializing the
remainder to zero in the case of zero division makes sense.
> do not use 64-bit math unnecessarily in __moddi3 and __divdi3.
>
> Reported-by: Alexandru Elisei <alexandru.elisei@arm.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
> lib/ldiv32.c | 28 +++++++++++++++++++++++++---
> 1 file changed, 25 insertions(+), 3 deletions(-)
>
> diff --git a/lib/ldiv32.c b/lib/ldiv32.c
> index 96f4b35..c39fccd 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. */
> @@ -35,9 +39,27 @@ uint64_t __udivmoddi4(uint64_t num, uint64_t den, uint64_t *p_rem)
> return quot;
> }
>
> +int64_t __divmoddi4(int64_t num, int64_t den, int64_t *p_rem)
> +{
> + 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 + nmask) ^ nmask;
> + if (den < 0)
> + den = -den;
> +
> + /* Copy sign of num^den into quotient, sign of num into remainder. */
> + quot = (__divmoddi4(num, den, p_rem) + qmask) ^ qmask;
I see no early return statement in the function, it looks to me like the function
will recurse forever. Maybe you wanted to call here __*u*divmoddi4() (emphasis
added) instead?
Other than that, the function looks correct.
Thanks,
Alex
> + if (p_rem)
> + *p_rem = (*p_rem + nmask) ^ nmask;
> + return quot;
> +}
> +
> int64_t __moddi3(int64_t num, int64_t den)
> {
> - uint64_t mask = num < 0 ? -1 : 0;
> + int32_t mask = num < 0 ? -1 : 0;
>
> /* Compute absolute values and do an unsigned division. */
> num = (num + mask) ^ mask;
> @@ -50,7 +72,7 @@ int64_t __moddi3(int64_t num, int64_t den)
>
> int64_t __divdi3(int64_t num, int64_t den)
> {
> - uint64_t mask = (num ^ den) < 0 ? -1 : 0;
> + int32_t mask = (num ^ den) < 0 ? -1 : 0;
>
> /* Compute absolute values and do an unsigned division. */
> if (num < 0)
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH kvm-unit-tests 1/2] libcflat: clean up and complete long division routines
2021-05-12 10:39 ` Alexandru Elisei
@ 2021-05-12 10:47 ` Paolo Bonzini
0 siblings, 0 replies; 5+ messages in thread
From: Paolo Bonzini @ 2021-05-12 10:47 UTC (permalink / raw)
To: Alexandru Elisei, kvm
On 12/05/21 12:39, Alexandru Elisei wrote:
>> +
>> + /* Copy sign of num^den into quotient, sign of num into remainder. */
>> + quot = (__divmoddi4(num, den, p_rem) + qmask) ^ qmask;
> I see no early return statement in the function, it looks to me like the function
> will recurse forever. Maybe you wanted to call here __*u*divmoddi4() (emphasis
> added) instead?
Of course...
Paolo
^ permalink raw reply [flat|nested] 5+ messages in thread
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2021-05-11 17:41 [PATCH kvm-unit-tests 0/2] fix long division routines for ARM eabi Paolo Bonzini
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2021-05-12 10:39 ` Alexandru Elisei
2021-05-12 10:47 ` Paolo Bonzini
2021-05-11 17:41 ` [PATCH kvm-unit-tests 2/2] arm: add eabi version of 64-bit division functions Paolo Bonzini
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