* [Qemu-devel] [Bug 1841442] Re: floating point emulation can fail to set FE_INEXACT
2019-08-26 15:00 [Qemu-devel] [Bug 1841442] [NEW] floating point emulation can fail to set FE_INEXACT Paul Clarke
@ 2019-08-26 15:31 ` Richard Henderson
2019-08-26 16:11 ` Alex Bennée
2019-08-26 15:57 ` Paul Clarke
` (3 subsequent siblings)
4 siblings, 1 reply; 8+ messages in thread
From: Richard Henderson @ 2019-08-26 15:31 UTC (permalink / raw)
To: qemu-devel
Well, maybe yes and maybe no. What you've done is choose two targets
whose floating point emulation have not been well maintained.
If I try this same test on aarch64, it passes:
$ ~/a.out 0x0000000000000001
0x0000000000000001 0.000000
0x0
0x18
FE_INEXACT FE_UNDERFLOW
0x0000000000000000 0.000000
$ ./aarch64-linux-user/qemu-aarch64 ~/a.out 0x0000000000000001
0x0000000000000001 0.000000
0x0
0x18
FE_INEXACT FE_UNDERFLOW
0x0000000000000000 0.000000
--
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https://bugs.launchpad.net/bugs/1841442
Title:
floating point emulation can fail to set FE_INEXACT
Status in QEMU:
New
Bug description:
Floating point emulation can fail to set FE_INEXACT in some
circumstances. This shows up quite often in glibc's "math" tests. A
similar test is attached.
On ppc64le native:
--
$ gcc nextafter.c -o nextafter -lm
$ ./nextafter $(./nextafter)
0x0000000000000001 0.000000
0x0
0xa000000
FE_INEXACT FE_UNDERFLOW
0x0000000000000000 0.000000
--
On x86_64:
--
$ gcc nextafter.c -o nextafter -lm
$ ./nextafter $(./nextafter)
0x0000000000000001 0.000000
0x0
0x30
FE_INEXACT FE_UNDERFLOW
0x0000000000000000 0.000000
--
Using qemu-system-ppc64
--
$ ./nextafter $(./nextafter)
0x0000000000000001 0.000000
0x0
0x8000000
FE_UNDERFLOW
0x0000000000000000 0.000000
--
Using qemu-x86_64:
--
$ ./nextafter $(./nextafter)
0x0000000000000001 0.000000
0x0
0x0
0x0000000000000000 0.000000
--
QEMU versions vary, but not too much, and are pretty close to git HEAD:
- 586f3dced9 (HEAD -> master, origin/master, origin/HEAD) Merge remote-tracking branch 'remotes/cohuck/tags/s390x-20190822' into staging
- 864ab31 Update version for v4.1.0-rc4 release
Since the issue happens nearly identically on different targets, I
suspect the issue lies somewhere in fpu/softfloat.c.
To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1841442/+subscriptions
^ permalink raw reply [flat|nested] 8+ messages in thread* Re: [Qemu-devel] [Bug 1841442] Re: floating point emulation can fail to set FE_INEXACT
@ 2019-08-26 16:11 ` Alex Bennée
0 siblings, 0 replies; 8+ messages in thread
From: Alex Bennée @ 2019-08-26 16:11 UTC (permalink / raw)
To: Bug 1841442; +Cc: qemu-devel
Richard Henderson <rth@twiddle.net> writes:
> Well, maybe yes and maybe no. What you've done is choose two targets
> whose floating point emulation have not been well maintained.
So this is a failure on the x86_64 and ppc64 frontends to correctly set
the softfloat modes when their appropriate registers are set?
>
> If I try this same test on aarch64, it passes:
>
> $ ~/a.out 0x0000000000000001
> 0x0000000000000001 0.000000
> 0x0
>
> 0x18
> FE_INEXACT FE_UNDERFLOW
> 0x0000000000000000 0.000000
>
> $ ./aarch64-linux-user/qemu-aarch64 ~/a.out 0x0000000000000001
> 0x0000000000000001 0.000000
> 0x0
>
> 0x18
> FE_INEXACT FE_UNDERFLOW
> 0x0000000000000000 0.000000
--
Alex Bennée
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [Qemu-devel] [Bug 1841442] Re: floating point emulation can fail to set FE_INEXACT
@ 2019-08-26 16:11 ` Alex Bennée
0 siblings, 0 replies; 8+ messages in thread
From: Alex Bennée @ 2019-08-26 16:11 UTC (permalink / raw)
To: qemu-devel
Richard Henderson <rth@twiddle.net> writes:
> Well, maybe yes and maybe no. What you've done is choose two targets
> whose floating point emulation have not been well maintained.
So this is a failure on the x86_64 and ppc64 frontends to correctly set
the softfloat modes when their appropriate registers are set?
>
> If I try this same test on aarch64, it passes:
>
> $ ~/a.out 0x0000000000000001
> 0x0000000000000001 0.000000
> 0x0
>
> 0x18
> FE_INEXACT FE_UNDERFLOW
> 0x0000000000000000 0.000000
>
> $ ./aarch64-linux-user/qemu-aarch64 ~/a.out 0x0000000000000001
> 0x0000000000000001 0.000000
> 0x0
>
> 0x18
> FE_INEXACT FE_UNDERFLOW
> 0x0000000000000000 0.000000
--
Alex Bennée
--
You received this bug notification because you are a member of qemu-
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https://bugs.launchpad.net/bugs/1841442
Title:
floating point emulation can fail to set FE_INEXACT
Status in QEMU:
New
Bug description:
Floating point emulation can fail to set FE_INEXACT in some
circumstances. This shows up quite often in glibc's "math" tests. A
similar test is attached.
On ppc64le native:
--
$ gcc nextafter.c -o nextafter -lm
$ ./nextafter $(./nextafter)
0x0000000000000001 0.000000
0x0
0xa000000
FE_INEXACT FE_UNDERFLOW
0x0000000000000000 0.000000
--
On x86_64:
--
$ gcc nextafter.c -o nextafter -lm
$ ./nextafter $(./nextafter)
0x0000000000000001 0.000000
0x0
0x30
FE_INEXACT FE_UNDERFLOW
0x0000000000000000 0.000000
--
Using qemu-system-ppc64
--
$ ./nextafter $(./nextafter)
0x0000000000000001 0.000000
0x0
0x8000000
FE_UNDERFLOW
0x0000000000000000 0.000000
--
Using qemu-x86_64:
--
$ ./nextafter $(./nextafter)
0x0000000000000001 0.000000
0x0
0x0
0x0000000000000000 0.000000
--
QEMU versions vary, but not too much, and are pretty close to git HEAD:
- 586f3dced9 (HEAD -> master, origin/master, origin/HEAD) Merge remote-tracking branch 'remotes/cohuck/tags/s390x-20190822' into staging
- 864ab31 Update version for v4.1.0-rc4 release
Since the issue happens nearly identically on different targets, I
suspect the issue lies somewhere in fpu/softfloat.c.
To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1841442/+subscriptions
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Qemu-devel] [Bug 1841442] Re: floating point emulation can fail to set FE_INEXACT
2019-08-26 15:00 [Qemu-devel] [Bug 1841442] [NEW] floating point emulation can fail to set FE_INEXACT Paul Clarke
2019-08-26 15:31 ` [Qemu-devel] [Bug 1841442] " Richard Henderson
@ 2019-08-26 15:57 ` Paul Clarke
2019-08-26 17:06 ` Richard Henderson
` (2 subsequent siblings)
4 siblings, 0 replies; 8+ messages in thread
From: Paul Clarke @ 2019-08-26 15:57 UTC (permalink / raw)
To: qemu-devel
Interesting. Did you run qemu-aarch64 on aarch64? If so, it may have
been using "hardfloat". I ran "qemu-system-ppc64" on x86_64 and "qemu-
x86_64" on ppc64le to ensure I was using "softfloat".
--
You received this bug notification because you are a member of qemu-
devel-ml, which is subscribed to QEMU.
https://bugs.launchpad.net/bugs/1841442
Title:
floating point emulation can fail to set FE_INEXACT
Status in QEMU:
New
Bug description:
Floating point emulation can fail to set FE_INEXACT in some
circumstances. This shows up quite often in glibc's "math" tests. A
similar test is attached.
On ppc64le native:
--
$ gcc nextafter.c -o nextafter -lm
$ ./nextafter $(./nextafter)
0x0000000000000001 0.000000
0x0
0xa000000
FE_INEXACT FE_UNDERFLOW
0x0000000000000000 0.000000
--
On x86_64:
--
$ gcc nextafter.c -o nextafter -lm
$ ./nextafter $(./nextafter)
0x0000000000000001 0.000000
0x0
0x30
FE_INEXACT FE_UNDERFLOW
0x0000000000000000 0.000000
--
Using qemu-system-ppc64
--
$ ./nextafter $(./nextafter)
0x0000000000000001 0.000000
0x0
0x8000000
FE_UNDERFLOW
0x0000000000000000 0.000000
--
Using qemu-x86_64:
--
$ ./nextafter $(./nextafter)
0x0000000000000001 0.000000
0x0
0x0
0x0000000000000000 0.000000
--
QEMU versions vary, but not too much, and are pretty close to git HEAD:
- 586f3dced9 (HEAD -> master, origin/master, origin/HEAD) Merge remote-tracking branch 'remotes/cohuck/tags/s390x-20190822' into staging
- 864ab31 Update version for v4.1.0-rc4 release
Since the issue happens nearly identically on different targets, I
suspect the issue lies somewhere in fpu/softfloat.c.
To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1841442/+subscriptions
^ permalink raw reply [flat|nested] 8+ messages in thread* [Qemu-devel] [Bug 1841442] Re: floating point emulation can fail to set FE_INEXACT
2019-08-26 15:00 [Qemu-devel] [Bug 1841442] [NEW] floating point emulation can fail to set FE_INEXACT Paul Clarke
2019-08-26 15:31 ` [Qemu-devel] [Bug 1841442] " Richard Henderson
2019-08-26 15:57 ` Paul Clarke
@ 2019-08-26 17:06 ` Richard Henderson
2019-08-26 17:09 ` Richard Henderson
2020-03-10 8:47 ` Laurent Vivier
4 siblings, 0 replies; 8+ messages in thread
From: Richard Henderson @ 2019-08-26 17:06 UTC (permalink / raw)
To: qemu-devel
> Interesting. Did you run qemu-aarch64 on aarch64? If so, it may have been
> using "hardfloat". I ran "qemu-system-ppc64" on x86_64 and "qemu-x86_64"
> on ppc64le to ensure I was using "softfloat".
That's not how that works. Indeed, the point of the hardfloat path is to
accelerate fpu emulation for a non-native guest.
That said, qemu-system-ppc64 will *never* use hardfloat, because ppc always
need the current and correct result of inexact for emulation of the FI bit,
which requires that we use the softfloat path.
Also, use of the hardfloat path requires normal inputs. For this test case
we're passing the minimum denormal input: 0x0000_0000_0000_0001. So we will
always use the softfloat path for this.
** Changed in: qemu
Status: New => Confirmed
--
You received this bug notification because you are a member of qemu-
devel-ml, which is subscribed to QEMU.
https://bugs.launchpad.net/bugs/1841442
Title:
floating point emulation can fail to set FE_INEXACT
Status in QEMU:
Confirmed
Bug description:
Floating point emulation can fail to set FE_INEXACT in some
circumstances. This shows up quite often in glibc's "math" tests. A
similar test is attached.
On ppc64le native:
--
$ gcc nextafter.c -o nextafter -lm
$ ./nextafter $(./nextafter)
0x0000000000000001 0.000000
0x0
0xa000000
FE_INEXACT FE_UNDERFLOW
0x0000000000000000 0.000000
--
On x86_64:
--
$ gcc nextafter.c -o nextafter -lm
$ ./nextafter $(./nextafter)
0x0000000000000001 0.000000
0x0
0x30
FE_INEXACT FE_UNDERFLOW
0x0000000000000000 0.000000
--
Using qemu-system-ppc64
--
$ ./nextafter $(./nextafter)
0x0000000000000001 0.000000
0x0
0x8000000
FE_UNDERFLOW
0x0000000000000000 0.000000
--
Using qemu-x86_64:
--
$ ./nextafter $(./nextafter)
0x0000000000000001 0.000000
0x0
0x0
0x0000000000000000 0.000000
--
QEMU versions vary, but not too much, and are pretty close to git HEAD:
- 586f3dced9 (HEAD -> master, origin/master, origin/HEAD) Merge remote-tracking branch 'remotes/cohuck/tags/s390x-20190822' into staging
- 864ab31 Update version for v4.1.0-rc4 release
Since the issue happens nearly identically on different targets, I
suspect the issue lies somewhere in fpu/softfloat.c.
To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1841442/+subscriptions
^ permalink raw reply [flat|nested] 8+ messages in thread* [Qemu-devel] [Bug 1841442] Re: floating point emulation can fail to set FE_INEXACT
2019-08-26 15:00 [Qemu-devel] [Bug 1841442] [NEW] floating point emulation can fail to set FE_INEXACT Paul Clarke
` (2 preceding siblings ...)
2019-08-26 17:06 ` Richard Henderson
@ 2019-08-26 17:09 ` Richard Henderson
2020-03-10 8:47 ` Laurent Vivier
4 siblings, 0 replies; 8+ messages in thread
From: Richard Henderson @ 2019-08-26 17:09 UTC (permalink / raw)
To: qemu-devel
Patch for ppc:
https://lists.gnu.org/archive/html/qemu-devel/2019-08/msg05532.html
Fixing x86_64 is significantly harder, as support for fp exceptions
is completely lacking in the code currently.
--
You received this bug notification because you are a member of qemu-
devel-ml, which is subscribed to QEMU.
https://bugs.launchpad.net/bugs/1841442
Title:
floating point emulation can fail to set FE_INEXACT
Status in QEMU:
Confirmed
Bug description:
Floating point emulation can fail to set FE_INEXACT in some
circumstances. This shows up quite often in glibc's "math" tests. A
similar test is attached.
On ppc64le native:
--
$ gcc nextafter.c -o nextafter -lm
$ ./nextafter $(./nextafter)
0x0000000000000001 0.000000
0x0
0xa000000
FE_INEXACT FE_UNDERFLOW
0x0000000000000000 0.000000
--
On x86_64:
--
$ gcc nextafter.c -o nextafter -lm
$ ./nextafter $(./nextafter)
0x0000000000000001 0.000000
0x0
0x30
FE_INEXACT FE_UNDERFLOW
0x0000000000000000 0.000000
--
Using qemu-system-ppc64
--
$ ./nextafter $(./nextafter)
0x0000000000000001 0.000000
0x0
0x8000000
FE_UNDERFLOW
0x0000000000000000 0.000000
--
Using qemu-x86_64:
--
$ ./nextafter $(./nextafter)
0x0000000000000001 0.000000
0x0
0x0
0x0000000000000000 0.000000
--
QEMU versions vary, but not too much, and are pretty close to git HEAD:
- 586f3dced9 (HEAD -> master, origin/master, origin/HEAD) Merge remote-tracking branch 'remotes/cohuck/tags/s390x-20190822' into staging
- 864ab31 Update version for v4.1.0-rc4 release
Since the issue happens nearly identically on different targets, I
suspect the issue lies somewhere in fpu/softfloat.c.
To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1841442/+subscriptions
^ permalink raw reply [flat|nested] 8+ messages in thread* [Bug 1841442] Re: floating point emulation can fail to set FE_INEXACT
2019-08-26 15:00 [Qemu-devel] [Bug 1841442] [NEW] floating point emulation can fail to set FE_INEXACT Paul Clarke
` (3 preceding siblings ...)
2019-08-26 17:09 ` Richard Henderson
@ 2020-03-10 8:47 ` Laurent Vivier
4 siblings, 0 replies; 8+ messages in thread
From: Laurent Vivier @ 2020-03-10 8:47 UTC (permalink / raw)
To: qemu-devel
Fixed by 16ce2fffa660 ("target/ppc: Fix do_float_check_status vs
inexact")
** Changed in: qemu
Status: Confirmed => Fix Released
--
You received this bug notification because you are a member of qemu-
devel-ml, which is subscribed to QEMU.
https://bugs.launchpad.net/bugs/1841442
Title:
floating point emulation can fail to set FE_INEXACT
Status in QEMU:
Fix Released
Bug description:
Floating point emulation can fail to set FE_INEXACT in some
circumstances. This shows up quite often in glibc's "math" tests. A
similar test is attached.
On ppc64le native:
--
$ gcc nextafter.c -o nextafter -lm
$ ./nextafter $(./nextafter)
0x0000000000000001 0.000000
0x0
0xa000000
FE_INEXACT FE_UNDERFLOW
0x0000000000000000 0.000000
--
On x86_64:
--
$ gcc nextafter.c -o nextafter -lm
$ ./nextafter $(./nextafter)
0x0000000000000001 0.000000
0x0
0x30
FE_INEXACT FE_UNDERFLOW
0x0000000000000000 0.000000
--
Using qemu-system-ppc64
--
$ ./nextafter $(./nextafter)
0x0000000000000001 0.000000
0x0
0x8000000
FE_UNDERFLOW
0x0000000000000000 0.000000
--
Using qemu-x86_64:
--
$ ./nextafter $(./nextafter)
0x0000000000000001 0.000000
0x0
0x0
0x0000000000000000 0.000000
--
QEMU versions vary, but not too much, and are pretty close to git HEAD:
- 586f3dced9 (HEAD -> master, origin/master, origin/HEAD) Merge remote-tracking branch 'remotes/cohuck/tags/s390x-20190822' into staging
- 864ab31 Update version for v4.1.0-rc4 release
Since the issue happens nearly identically on different targets, I
suspect the issue lies somewhere in fpu/softfloat.c.
To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1841442/+subscriptions
^ permalink raw reply [flat|nested] 8+ messages in thread