musl - qsort() issue on ARM

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Date: Tue, 23 Jul 2019 16:09:04 +0200
From: "piotr.krzysztof.gawel" <piotr.krzysztof.gawel@...il.com>
To: musl@...ts.openwall.com
Subject: qsort() issue on ARM

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

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Download attachment "qsort.c" of type "application/c" (1430 bytes)

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