Messages in this thread | | | Date | Thu, 22 Sep 2022 18:15:50 +0000 | From | Sean Christopherson <> | Subject | Re: [PATCH 0/5] KVM: selftests: Fix "fix hypercall test" build errors |
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On Thu, Sep 22, 2022, Jim Mattson wrote: > On Thu, Sep 22, 2022 at 10:20 AM David Matlack <dmatlack@google.com> wrote: > > > > On Thu, Sep 8, 2022 at 4:34 PM Sean Christopherson <seanjc@google.com> wrote: > > > > > > After a toolchain upgrade (I think), 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. > > > > Ah ha! This also fixes an issue I've long since noticed and finally > > got around to debugging this morning. userspace_io_test fails for me > > when built with Clang but passes with GCC. It turns out Clang > > generates a call to <memset@plt>, whereas GCC directly generates rep > > stos, to clear @buffer in guest_code(). > > Hey! Did I miss a revert of commit ed290e1c20da ("KVM: selftests: Fix > nested SVM tests when built with clang") in that patch set?
LOL, no, no you did not. I'll do that in v2.
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