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| author | Vitaly Kuznetsov <vkuznets@redhat.com> | 2019-10-08 20:08:08 +0200 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2019-10-22 13:31:18 +0200 |
| commit | ef4059809890f732c69cc1726d3a9a108a832a2f (patch) | |
| tree | 6ac0a5e1d902568a9a4cc374a5c34d7107ee2e2b /tools | |
| parent | 11eada4718a352a6a588de9908200c1e348530f1 (diff) | |
| download | linux-stable-ef4059809890f732c69cc1726d3a9a108a832a2f.tar.gz linux-stable-ef4059809890f732c69cc1726d3a9a108a832a2f.tar.bz2 linux-stable-ef4059809890f732c69cc1726d3a9a108a832a2f.zip | |
selftests: kvm: fix sync_regs_test with newer gccs
Commit 204c91eff798a ("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: 204c91eff798a ("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>
Diffstat (limited to 'tools')
| -rw-r--r-- | tools/testing/selftests/kvm/x86_64/sync_regs_test.c | 21 |
1 files changed, 11 insertions, 10 deletions
diff --git a/tools/testing/selftests/kvm/x86_64/sync_regs_test.c b/tools/testing/selftests/kvm/x86_64/sync_regs_test.c index 11c2a70a7b87..5c8224256294 100644 --- a/tools/testing/selftests/kvm/x86_64/sync_regs_test.c +++ b/tools/testing/selftests/kvm/x86_64/sync_regs_test.c @@ -22,18 +22,19 @@ #define VCPU_ID 5 +#define UCALL_PIO_PORT ((uint16_t)0x1000) + +/* + * ucall is embedded here to protect against compiler reshuffling registers + * before calling a function. In this test we only need to get KVM_EXIT_IO + * vmexit and preserve RBX, no additional information is needed. + */ void guest_code(void) { - /* - * use a callee-save register, otherwise the compiler - * saves it around the call to GUEST_SYNC. - */ - register u32 stage asm("rbx"); - for (;;) { - GUEST_SYNC(0); - stage++; - asm volatile ("" : : "r" (stage)); - } + asm volatile("1: in %[port], %%al\n" + "add $0x1, %%rbx\n" + "jmp 1b" + : : [port] "d" (UCALL_PIO_PORT) : "rax", "rbx"); } static void compare_regs(struct kvm_regs *left, struct kvm_regs *right) |