* qsort() issue on ARM
@ 2019-07-23 14:09 piotr.krzysztof.gawel
2019-07-23 14:24 ` Rich Felker
0 siblings, 1 reply; 3+ messages in thread
From: piotr.krzysztof.gawel @ 2019-07-23 14:09 UTC (permalink / raw)
To: musl
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Hi MUSL developers,
I encountered an issue when running LTP tests on my ARM A15 machine. Tests executed with tst_timer_test where dumping cores. Further analysis of tst_timer_test.c file led me to qsort() function which they call. Their
code relies on sorted array.
I wrote a sample application which you may find in attachment. Here is the output from that tool on my machine:
# /media/qsort
Before sorting:
00: 100126
01: 100193
02: 100143
03: 100131
04: 100129
05: 100129
06: 100128
07: 100128
08: 100125
09: 100125
Samples number: 10, width: 8
cmp: comparing 100143 with 100126 (0)
...
cmp: comparing 100143 with 100131 (0)
cmp: comparing 100126 with 100193 (1)
After sorting:
00: 100193
01: 100126
02: 100143
03: 100131
04: 100129
05: 100129
06: 100128
07: 100128
08: 100125
09: 100125
Before sorting:
00: 100126
01: 100193
02: 100143
03: 100131
04: 100129
05: 100129
06: 100128
07: 100128
08: 100125
09: 100125
Samples number: 10, width: 8
cmp: comparing 100143 with 100126 (0)
...
cmp: comparing 100126 with 100193 (1)
After sorting:
00: 100193
01: 100126
02: 100143
03: 100131
04: 100129
05: 100129
06: 100128
07: 100128
08: 100125
09: 100125
Observations from that output:
comparison function works as expectedarray is sorted from max to min value as expected except second item (index 01) which looks like a bugarray on heap and stack presents exactly the same problem
In case of LTP, the issue was more random – it was not always second item in wrong position, items were more disordered.
When I compiled the testing app for my PC (x86_64) with GNU libc (Ubuntu), array was sorted correctly.
I use gcc toolchain from Yocto. Whole image, including toolchain, LTP and musl are built with Yocto.
Thanks for any help or suggestion in advance! I’m looking forward to hear from you if this is machine/architecture related issue, or if you can see it also in your system. Please also add me to replies if possible since I am not subscribed to mailing list.
Best regards,
Piotr Gawel
null
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^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: qsort() issue on ARM
2019-07-23 14:09 qsort() issue on ARM piotr.krzysztof.gawel
@ 2019-07-23 14:24 ` Rich Felker
2019-07-23 15:14 ` Piotr Gaweł
0 siblings, 1 reply; 3+ messages in thread
From: Rich Felker @ 2019-07-23 14:24 UTC (permalink / raw)
To: piotr.krzysztof.gawel; +Cc: musl
On Tue, Jul 23, 2019 at 04:09:04PM +0200, piotr.krzysztof.gawel wrote:
> Hi MUSL developers,
>
> I encountered an issue when running LTP tests on my ARM A15 machine. Tests executed with tst_timer_test where dumping cores. Further analysis of tst_timer_test.c file led me to qsort() function which they call. Their
> code relies on sorted array.
> I wrote a sample application which you may find in attachment. Here is the output from that tool on my machine:
> # /media/qsort
> Before sorting:
> 00: 100126
> 01: 100193
> 02: 100143
> 03: 100131
> 04: 100129
> 05: 100129
> 06: 100128
> 07: 100128
> 08: 100125
> 09: 100125
>
> Samples number: 10, width: 8
> cmp: comparing 100143 with 100126 (0)
> ...
> cmp: comparing 100143 with 100131 (0)
> cmp: comparing 100126 with 100193 (1)
>
>
> After sorting:
> 00: 100193
> 01: 100126
> 02: 100143
> 03: 100131
> 04: 100129
> 05: 100129
> 06: 100128
> 07: 100128
> 08: 100125
> 09: 100125
> Before sorting:
> 00: 100126
> 01: 100193
> 02: 100143
> 03: 100131
> 04: 100129
> 05: 100129
> 06: 100128
> 07: 100128
> 08: 100125
> 09: 100125
>
> Samples number: 10, width: 8
> cmp: comparing 100143 with 100126 (0)
> ...
> cmp: comparing 100126 with 100193 (1)
>
>
> After sorting:
> 00: 100193
> 01: 100126
> 02: 100143
> 03: 100131
> 04: 100129
> 05: 100129
> 06: 100128
> 07: 100128
> 08: 100125
> 09: 100125
>
> Observations from that output:
>
> comparison function works as expectedarray is sorted from max to min
> value as expected except second item (index 01) which looks like a
> bugarray on heap and stack presents exactly the same problem
>
> In case of LTP, the issue was more random – it was not always second
> item in wrong position, items were more disordered.
> When I compiled the testing app for my PC (x86_64) with GNU libc
> (Ubuntu), array was sorted correctly.
>
> I use gcc toolchain from Yocto. Whole image, including toolchain,
> LTP and musl are built with Yocto.
>
> Thanks for any help or suggestion in advance! I’m looking forward to
> hear from you if this is machine/architecture related issue, or if
> you can see it also in your system. Please also add me to replies if
> possible since I am not subscribed to mailing list.
Their code just has undefined behavior by violating the contract of
qsort with the cmp function they submit to it:
https://github.com/linux-test-project/ltp/blob/4053a2551b926d372dd47485f7381ec3fa19772a/lib/tst_timer_test.c#L170
qsort requires that the comparison return a negative, zero, or
positive value depending on whether the relationship is less-than,
equal, or greater-than. In particular, if cmp(a,b) is positive,
cmp(b,a) must be negative, and vice versa. In one direction,
cmp(100126,100193) is reporting them unequal, while in the other
direction, cmp(100193,100126) is reporting them equal.
FYI, LTP (and the OPTS code lots of it is derived from) has *lots* of
UB/invalid-tests...
Rich
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: qsort() issue on ARM
2019-07-23 14:24 ` Rich Felker
@ 2019-07-23 15:14 ` Piotr Gaweł
0 siblings, 0 replies; 3+ messages in thread
From: Piotr Gaweł @ 2019-07-23 15:14 UTC (permalink / raw)
To: Rich Felker; +Cc: musl
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Good point. Thank You very much Rich! I already noticed that LTP has a lot
of bugs. I will fix it in my distribution.
Many thanks for the support.
Have a nice day.
Best regards,
Piotr
wt., 23 lip 2019, 16:24 użytkownik Rich Felker <dalias@libc.org> napisał:
> On Tue, Jul 23, 2019 at 04:09:04PM +0200, piotr.krzysztof.gawel wrote:
> > Hi MUSL developers,
> >
> > I encountered an issue when running LTP tests on my ARM A15 machine.
> Tests executed with tst_timer_test where dumping cores. Further analysis of
> tst_timer_test.c file led me to qsort() function which they call. Their
> > code relies on sorted array.
> > I wrote a sample application which you may find in attachment. Here is
> the output from that tool on my machine:
> > # /media/qsort
> > Before sorting:
> > 00: 100126
> > 01: 100193
> > 02: 100143
> > 03: 100131
> > 04: 100129
> > 05: 100129
> > 06: 100128
> > 07: 100128
> > 08: 100125
> > 09: 100125
> >
> > Samples number: 10, width: 8
> > cmp: comparing 100143 with 100126 (0)
> > ...
> > cmp: comparing 100143 with 100131 (0)
> > cmp: comparing 100126 with 100193 (1)
> >
> >
> > After sorting:
> > 00: 100193
> > 01: 100126
> > 02: 100143
> > 03: 100131
> > 04: 100129
> > 05: 100129
> > 06: 100128
> > 07: 100128
> > 08: 100125
> > 09: 100125
> > Before sorting:
> > 00: 100126
> > 01: 100193
> > 02: 100143
> > 03: 100131
> > 04: 100129
> > 05: 100129
> > 06: 100128
> > 07: 100128
> > 08: 100125
> > 09: 100125
> >
> > Samples number: 10, width: 8
> > cmp: comparing 100143 with 100126 (0)
> > ...
> > cmp: comparing 100126 with 100193 (1)
> >
> >
> > After sorting:
> > 00: 100193
> > 01: 100126
> > 02: 100143
> > 03: 100131
> > 04: 100129
> > 05: 100129
> > 06: 100128
> > 07: 100128
> > 08: 100125
> > 09: 100125
> >
> > Observations from that output:
> >
> > comparison function works as expectedarray is sorted from max to min
> > value as expected except second item (index 01) which looks like a
> > bugarray on heap and stack presents exactly the same problem
> >
> > In case of LTP, the issue was more random – it was not always second
> > item in wrong position, items were more disordered.
> > When I compiled the testing app for my PC (x86_64) with GNU libc
> > (Ubuntu), array was sorted correctly.
> >
> > I use gcc toolchain from Yocto. Whole image, including toolchain,
> > LTP and musl are built with Yocto.
> >
> > Thanks for any help or suggestion in advance! I’m looking forward to
> > hear from you if this is machine/architecture related issue, or if
> > you can see it also in your system. Please also add me to replies if
> > possible since I am not subscribed to mailing list.
>
> Their code just has undefined behavior by violating the contract of
> qsort with the cmp function they submit to it:
>
>
> https://github.com/linux-test-project/ltp/blob/4053a2551b926d372dd47485f7381ec3fa19772a/lib/tst_timer_test.c#L170
>
> qsort requires that the comparison return a negative, zero, or
> positive value depending on whether the relationship is less-than,
> equal, or greater-than. In particular, if cmp(a,b) is positive,
> cmp(b,a) must be negative, and vice versa. In one direction,
> cmp(100126,100193) is reporting them unequal, while in the other
> direction, cmp(100193,100126) is reporting them equal.
>
> FYI, LTP (and the OPTS code lots of it is derived from) has *lots* of
> UB/invalid-tests...
>
> Rich
>
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^ permalink raw reply [flat|nested] 3+ messages in thread
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2019-07-23 14:09 qsort() issue on ARM piotr.krzysztof.gawel
2019-07-23 14:24 ` Rich Felker
2019-07-23 15:14 ` Piotr Gaweł
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