On 30/09/21 02:36, Jim Mattson wrote:
Though gcc conveniently compiles a simple memset to "rep stos," clang prefers to call the libc version of memset. If a test is dynamically linked, the libc memset isn't available in L1 (nor is the PLT or the GOT, for that matter). Even if the test is statically linked, the libc memset may choose to use some CPU features, like AVX, which may not be enabled in L1. Note that __builtin_memset doesn't solve the problem, because (a) the compiler is free to call memset anyway, and (b) __builtin_memset may also choose to use features like AVX, which may not be available in L1. To avoid a myriad of problems, use an explicit "rep stos" to clear the VMCB in generic_svm_setup(), which is called both from L0 and L1.
Queued, thanks. It would be nice if llvm at least had gcc's -minline-all-stringops and/or -mstringop-strategy=rep_byte, but even on gcc it wasn't really sure to work without those options.
Paolo
