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@xxxxxxxxxx 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
