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stack smashing in or after recvmsg system call in aarch64 user mode

A program that invokes recvmsg aborts with "*** stack smashing detected ***" when run in qemu-aarch64 (user mode), but works fine when running on native aarch64 hardware.

How to reproduce:
$ aarch64-linux-gnu-gcc-5 -O -Wall /media/develdata/devel/qemu-bug/testpassfd.c -static -DEXTRA_SPACE=0
$ QEMU_LD_PREFIX=/usr/aarch64-linux-gnu ~/inst-qemu/2.9.0/bin/qemu-aarch64 ./a.out
*** stack smashing detected ***: ./a.out terminated
qemu: uncaught target signal 6 (Aborted) - core dumped

On native aarch64 hardware:
$ ./a.out 
$ echo $?
0

The parameter EXTRA_SPACE can be used to add additional space to the array that receives the recvmsg data. With -DEXTRA_SPACE=9 (or larger), the program runs fine. Which suggests that recvmsg is storing up to 9 bytes more than allowed in memory.





Likewise for 32-bit arm:
$ ~/inst-qemu/2.9.0/bin/qemu-arm ./a.arm 
*** stack smashing detected ***: ./a.arm terminated
qemu: uncaught target signal 6 (Aborted) - core dumped


The behaviour in qemu-2.10 is the same as in qemu-2.9.

The behaviour in qemu-2.11 is the same as in qemu-2.9.

This should be fixed by http://patchwork.ozlabs.org/patch/849170/ I think.


Patch has been included here:
https://git.qemu.org/?p=qemu.git;a=commitdiff;h=7174970a94df10ee84143

Confirmed: It's fixed in qemu-2.12.