[PATCH v2 0/7] KVM: selftests: Fix "fix hypercall test" build errors

[Sean Christopherson <seanjc@google.com>]

After a toolchain upgrade, the x86 fix_hypercall_test started throwing
warnings due to -Werror=array-bounds rightly complaining that the test is
generating an out-of-bounds array access.

The "obvious" fix is to replace the memcpy() with a memcmp() and compare
only the exact size of the hypercall instruction.  That worked, until I
fiddled with the code a bit more and suddenly the test started jumping into
the weeds due to gcc generating a call to the external memcmp() through the
PLT, which isn't supported in the selftests.

To fix that mess, which has been a pitfall for quite some time, provide
implementations of memcmp(), memcpy(), and memset() to effectively override
the compiler built-ins.  My thought is to start with the helpers that are
most likely to be used in guest code, and then add more as needed.

v2:
 - Revert a patch that avoided memset(). [Jim]
 - Collect reviews. [Oliver]
 - Rename kvm_string.c => string_overrides.c. [David]
 - Tweak the "fix hypercall" test to verify that the original opcode
   is preserved exactly. [Oliver]
 - Further dedup code in the "fix hypercall" test.

v1: https://lore.kernel.org/all/20220908233134.3523339-1-seanjc@google.com

Sean Christopherson (7):
  KVM: selftests: Implement memcmp(), memcpy(), and memset() for guest
    use
  KVM: selftests: Compare insn opcodes directly in fix_hypercall_test
  KVM: selftests: Remove unnecessary register shuffling in
    fix_hypercall_test
  KVM: selftests: Hardcode VMCALL/VMMCALL opcodes in "fix hypercall"
    test
  KVM: selftests: Explicitly verify KVM doesn't patch hypercall if
    quirk==off
  KVM: selftests: Dedup subtests of fix_hypercall_test
  Revert "KVM: selftests: Fix nested SVM tests when built with clang"

 tools/testing/selftests/kvm/Makefile          |  11 +-
 .../selftests/kvm/lib/string_override.c       |  39 +++++
 tools/testing/selftests/kvm/lib/x86_64/svm.c  |  14 +-
 .../selftests/kvm/x86_64/fix_hypercall_test.c | 134 +++++++-----------
 4 files changed, 103 insertions(+), 95 deletions(-)
 create mode 100644 tools/testing/selftests/kvm/lib/string_override.c


base-commit: c59fb127583869350256656b7ed848c398bef879
-- 
2.37.3.998.g577e59143f-goog