[Bug server/30387] gdbserver assert error on arm platform

["kevinb at redhat dot com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=30387

--- Comment #24 from Kevin Buettner <kevinb at redhat dot com> ---
I did some testing and found that with the loop count (for the 'next'
commands) set to 200, it would take my Raspberry Pi, using
--target_board=native-gdbserver, nearly seven minutes to run the new
test, gdb.threads/next-fork-exec-other-thread.exp.  My macbook running
F38 would take nearly a minute and a half while an x86-64 VM also
running F38 would run the test in a little under a minute.

After a bunch of testing, I settled on changing that loop count to
30.  This would still reliably reproduce the bug that Zhiyong had
reported, but also finished considerably more quickly.  The Raspberry
Pi would finish in under a minute and a half while the macbook and
the x86-64 VM would finish in around 15 seconds. Native testing for
these targets completes in less than 10 seconds.

Therefore, in the interest of not causing overall testing to slow
down too much, I've reduced the loop count from 200 to 30.

My complete findings are below - stop here for the TLDR version!...

Command used for native-gdbserver:

time make check RUNTESTFLAGS="--target_board=native-gdbserver"
TESTS=gdb.threads/next-fork-exec-other-thread.exp

Command used for native:

time make check RUNTESTFLAGS=""
TESTS=gdb.threads/next-fork-exec-other-thread.exp

200 iterations:

rpi, unpatched, native-gdbserver: 2m51.976s (14 failures reported)
rpi, patched, native-gdbserver:   6m48.753s (2 failures reported)
rpi, unpatched, native:           2m11.673s 
rpi, patched, native:             2m9.436s

macbook, unpatched, native-gdbserver: 1m24.372s
macbook, patched, native-gdbserver:   1m26.793s
macbook, unpatched, native:           0m17.314s
macbook, patched, native:             0m18.017s

f38-1, unpatched, native-gdbserver: 0m55.265s
f38-1, patched, native-gdbserver:   0m52.767s
f38-1, unpatched, native:           0m23.419s
f38-1, patched, native:             0m23.119s

150 iterations:

rpi, unpatched, native-gdbserver: 2m31.826s (13 failures reported)
rpi, patched, native-gdbserver:   5m3.467s (2 failures reported)
rpi, unpatched, native:           1m43.856s
rpi, patched, native:             1m41.656s

macbook, unpatched, native-gdbserver: 1m9.472s
macbook, patched, native-gdbserver:   1m13.066s
macbook, unpatched, native:           0m13.646s
macbook, patched, native:             0m13.460s

f38-1, unpatched, native-gdbserver: 0m42.931s
f38-1, patched, native-gdbserver:   0m42.484s
f38-1, unpatched, native:           0m20.117s
f38-1, patched, native:             0m19.720s

100 iterations:

rpi, unpatched, native-gdbserver: 2m4.937s (13 failures reported)
rpi, patched, native-gdbserver:   3m56.154s (1 failure reported)
rpi, unpatched, native:           1m16.185s
rpi, patched, native:             1m14.161s

macbook, unpatched, native-gdbserver: 0m44.304s
macbook, patched, native-gdbserver:   0m41.998s
macbook, unpatched, native:           0m9.782s
macbook, patched, native:             0m10.400s

f38-1, unpatched, native-gdbserver: 0m30.188s
f38-1, patched, native-gdbserver:   0m30.122s
f38-1, unpatched, native:           0m15.375s
f38-1, patched, native:             0m15.306s

50 iterations:

rpi, unpatched, native-gdbserver: 1m22.541s (13 failures reported)
rpi, patched, native-gdbserver:   1m4.468s ( 1 failure reported)
rpi, unpatched, native:           0m48.767s
rpi, patched, native:             0m46.831s

macbook, unpatched, native-gdbserver: 0m25.266s
macbook, patched, native-gdbserver:   0m24.684s
macbook, unpatched, native:           0m6.302s
macbook, patched, native:             0m6.542s

f38-1, unpatched, native-gdbserver: 0m19.392s
f38-1, patched, native-gdbserver:   0m19.449s
f38-1, unpatched, native:           0m11.191s
f38-1, patched, native:             0m11.409s

30 iterations:

rpi, unpatched, native-gdbserver: 1m3.633s (12 failures reported)
rpi, patched, native-gdbserver:   1m27.072s (0 failures reported!)
rpi, unpatched, native:           0m37.846s
rpi, patched, native:             0m35.950s

macbook, unpatched, native-gdbserver: 0m14.870s
macbook, patched, native-gdbserver:   0m14.537s
macbook, unpatched, native:           0m4.605s
macbook, patched, native:             0m4.770s

f38-1, unpatched, native-gdbserver: 0m15.249s
f38-1, patched, native-gdbserver:   0m14.830s
f38-1, unpatched, native:           0m9.762s
f38-1, patched, native:             0m9.674s

20 iterations:

rpi, unpatched, native-gdbserver: 0m53.582s (11 failures reported)
rpi, patched, native-gdbserver:   1m5.585s (0 failures reported)
rpi, unpatched, native:           0m32.360s
rpi, patched, native:             0m30.554s

macbook, unpatched, native-gdbserver: 0m10.432s
macbook, patched, native-gdbserver:   0m10.776s
macbook, unpatched, native:           0m4.029s
macbook, patched, native:             0m4.189s

f38-1, unpatched, native-gdbserver: 0m12.492s
f38-1, patched, native-gdbserver:   0m12.477s
f38-1, unpatched, native:           0m8.801s
f38-1, patched, native:             0m8.729s

Back to 30 iterations, only rpi w/ native-gdbserver, multiple runs:

rpi, unpatched, native-gdbserver:

0m51.597s       : 13 failures, 12 core files
0m54.998s       : 13 failures, 12 core files
1m0.335s        : 12 failures, 12 core files
0m54.722s       : 12 failures, 11 core files
0m55.992s       : 12 failures, 12 core files

rpi, patched, native-gdbserver:

1m27.186s       : no failures
1m27.660s       : no failures
1m28.207s       : no failures
1m26.833s       : no failures
1m27.291s       : no failures

But note that no failures noted above doesn't mean that there isn't a
problem!  We just haven't iterated through enough GDB 'next' commands
to see it.

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