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Commit204c91eff7("KVM: selftests: do not blindly clobber registers in guest asm") was intended to make test more gcc-proof, however, the result is exactly the opposite: on newer gccs (e.g. 8.2.1) the test breaks with ==== Test Assertion Failure ==== x86_64/sync_regs_test.c:168: run->s.regs.regs.rbx == 0xBAD1DEA + 1 pid=14170 tid=14170 - Invalid argument 1 0x00000000004015b3: main at sync_regs_test.c:166 (discriminator 6) 2 0x00007f413fb66412: ?? ??:0 3 0x000000000040191d: _start at ??:? rbx sync regs value incorrect 0x1. Apparently, compile is still free to play games with registers even when they have variables attached. Re-write guest code with 'asm volatile' by embedding ucall there and making sure rbx is preserved. Fixes:204c91eff7("KVM: selftests: do not blindly clobber registers in guest asm") Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.