Add README.md file to rsabigexponent system test

This README.md describes why is bigkey needed.

(cherry picked from commit a247f24d)
89 jobs for !4632 with mnowak/add-rsabigexponent-README-v9_11 in 21 minutes (queued for 8 seconds)
detached
Status Job ID Name Coverage
  Precheck
passed #1444257
linux amd64
autoreconf

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passed #1444259
linux amd64
clang-format

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linux amd64
coccinelle

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linux amd64
danger

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linux amd64
misc

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  Build
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linux amd64
clang:asan

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clang:buster:amd64

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amd64 libvirt
clang:freebsd11:amd64

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amd64 libvirt
clang:freebsd12:amd64

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amd64 libvirt
clang:openbsd:amd64

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linux amd64
clang:tsan

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passed #1444280
linux amd64
clang:tsan:noatomics

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linux amd64
gcc:alpine3.12:amd64

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linux amd64
gcc:asan

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linux amd64
gcc:buster:amd64

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linux amd64
gcc:centos6:amd64

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linux i386
gcc:centos6:i386

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linux amd64
gcc:centos7:amd64

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linux amd64
gcc:centos8:amd64

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linux amd64
gcc:fedora33:amd64

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passed #1444274
linux amd64
gcc:focal:amd64

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passed #1444281
linux amd64
gcc:mutexatomics

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linux amd64
gcc:noatomics

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passed #1444270
linux amd64
gcc:out-of-tree

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passed #1444284
linux amd64
gcc:pkcs11

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passed #1444269
linux amd64
gcc:sid:amd64

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passed #1444267
linux amd64
gcc:stretch:amd64

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passed #1444277
linux amd64
gcc:tsan

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linux amd64
gcc:tsan:noatomics

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passed #1444271
linux amd64
gcc:tumbleweed:amd64

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passed #1444273
linux amd64
gcc:xenial:amd64

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amd64 windows
msvc:windows:amd64

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linux amd64
nolibtool:sid:amd64

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  Unit
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linux amd64
unit:clang:asan

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linux amd64
unit:clang:buster:amd64

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amd64 libvirt
unit:clang:freebsd11:amd64

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amd64 libvirt
unit:clang:freebsd12:amd64

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passed #1444305
linux amd64
unit:clang:tsan

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passed #1444307
linux amd64
unit:clang:tsan:noatomics

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passed #1444290
linux amd64
unit:gcc:alpine3.12:amd64

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passed #1444302
linux amd64
unit:gcc:asan

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passed #1444296
linux amd64
unit:gcc:buster:amd64

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linux amd64
unit:gcc:centos6:amd64

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passed #1444291
linux i386
unit:gcc:centos6:i386

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passed #1444293
linux amd64
unit:gcc:centos7:amd64

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passed #1444294
linux amd64
unit:gcc:centos8:amd64

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passed #1444299
linux amd64
unit:gcc:fedora33:amd64

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passed #1444301
linux amd64
unit:gcc:focal:amd64

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passed #1444308
linux amd64
unit:gcc:mutexatomics

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passed #1444309
linux amd64
unit:gcc:noatomics

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passed #1444311
linux amd64
unit:gcc:pkcs11

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linux amd64
unit:gcc:sid:amd64

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passed #1444295
linux amd64
unit:gcc:stretch:amd64

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passed #1444304
linux amd64
unit:gcc:tsan

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linux amd64
unit:gcc:tsan:noatomics

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linux amd64
unit:gcc:tumbleweed:amd64

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linux amd64
unit:gcc:xenial:amd64

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passed #1444314
linux amd64
unit:nolibtool:sid:amd64

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  System
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linux amd64
system:clang:asan

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linux amd64
system:clang:buster:amd64

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amd64 libvirt
system:clang:freebsd11:amd64

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passed #1444338
amd64 libvirt
system:clang:freebsd12:amd64

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passed #1444330
linux amd64
system:clang:tsan

00:11:23

failed #1444332
linux amd64 allowed to fail
system:clang:tsan:noatomics

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passed #1444315
linux amd64
system:gcc:alpine3.12:amd64

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passed #1444327
linux amd64
system:gcc:asan

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linux amd64
system:gcc:buster:amd64

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linux amd64
system:gcc:centos6:amd64

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linux i386
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linux amd64
system:gcc:centos7:amd64

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linux amd64
system:gcc:centos8:amd64

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linux amd64
system:gcc:fedora33:amd64

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linux amd64
system:gcc:focal:amd64

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linux amd64
system:gcc:mutexatomics

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linux amd64
system:gcc:noatomics

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linux amd64
system:gcc:pkcs11

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linux amd64
system:gcc:sid:amd64

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linux amd64
system:gcc:stretch:amd64

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passed #1444329
linux amd64
system:gcc:tsan

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linux amd64
system:gcc:tsan:noatomics

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linux amd64
system:gcc:tumbleweed:amd64

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linux amd64
system:gcc:xenial:amd64

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passed #1444339
linux amd64
system:nolibtool:sid:amd64

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  Docs
passed #1444340
linux amd64
docs

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  Postcheck
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linux amd64
cppcheck

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passed #1444341
linux amd64
flake8

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passed #1444345
linux amd64
gcov

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74.0%
passed #1444342
linux amd64
pylint

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passed #1444343
linux amd64
scan-build

00:09:30

 
Name Stage Failure
failed
system:clang:tsan:noatomics System
Running after_script
Running after script...
$ find bin -name 'tsan.*' -exec python3 util/parse_tsan.py {} \;
Uploading artifacts for failed job
Uploading artifacts...
untracked: found 1450 files

Uploading artifacts as "archive" to coordinator... ok
id=1444332 responseStatus=201 Created token=rcF3Jznh
Cleaning up file based variables
ERROR: Job failed: exit code 1