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    SubjectRe: [RFC PATCH v2 03/17] KVM: selftest: Adding TDX life cycle test.
    On Wed, Aug 31, 2022, Isaku Yamahata wrote:
    > Sometimes compiler (my gcc is (Ubuntu 11.1.0-1ubuntu1~20.04) 11.1.0) doesn't like
    > clobering the frame pointer as follows. (I edited the caller site for other test.)
    >
    > x86_64/tdx_vm_tests.c:343:1: error: bp cannot be used in ‘asm’ here
    >
    > I ended up the following workaround. I didn't use pushq/popq pair because
    > I didn't want to play with offset in the stack of the caller.
    >
    >
    > diff --git a/tools/testing/selftests/kvm/lib/x86_64/tdx.h b/tools/testing/selftests/kvm/lib/x86_64/tdx.h
    > index aa6961c6f304..8ddf3b64f003 100644
    > --- a/tools/testing/selftests/kvm/lib/x86_64/tdx.h
    > +++ b/tools/testing/selftests/kvm/lib/x86_64/tdx.h
    > @@ -122,7 +122,11 @@ void prepare_source_image(struct kvm_vm *vm, void *guest_code,
    > */
    > static inline void tdcall(struct kvm_regs *regs)
    > {
    > + unsigned long saved_rbp = 0;
    > +
    > asm volatile (
    > + /* gcc complains that frame pointer %rbp can't be clobbered. */
    > + "movq %%rbp, %28;\n\t"
    > "mov %13, %%rax;\n\t"
    > "mov %14, %%rbx;\n\t"
    > "mov %15, %%rcx;\n\t"
    > @@ -152,6 +156,8 @@ static inline void tdcall(struct kvm_regs *regs)
    > "mov %%r15, %10;\n\t"
    > "mov %%rsi, %11;\n\t"
    > "mov %%rdi, %12;\n\t"
    > + "movq %28, %%rbp\n\t"
    > + "movq $0, %28\n\t"
    > : "=m" (regs->rax), "=m" (regs->rbx), "=m" (regs->rdx),
    > "=m" (regs->r8), "=m" (regs->r9), "=m" (regs->r10),
    > "=m" (regs->r11), "=m" (regs->r12), "=m" (regs->r13),
    > @@ -161,9 +167,10 @@ static inline void tdcall(struct kvm_regs *regs)
    > "m" (regs->rdx), "m" (regs->r8), "m" (regs->r9),
    > "m" (regs->r10), "m" (regs->r11), "m" (regs->r12),
    > "m" (regs->r13), "m" (regs->r14), "m" (regs->r15),
    > - "m" (regs->rbp), "m" (regs->rsi), "m" (regs->rdi)
    > + "m" (regs->rbp), "m" (regs->rsi), "m" (regs->rdi),
    > + "m" (saved_rbp)
    > : "rax", "rbx", "rcx", "rdx", "r8", "r9", "r10", "r11",
    > - "r12", "r13", "r14", "r15", "rbp", "rsi", "rdi");
    > + "r12", "r13", "r14", "r15", "rsi", "rdi");
    > }

    Inline assembly for TDCALL is going to be a mess. Assuming proper assembly doesn't
    Just Work for selftests, we should solve that problem and build this on top.

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