https://sourceware.org/bugzilla/show_bug.cgi?id=32462
--- Comment #1 from Michael Clark <michaeljclark at mac dot com> ---
QEMU ignores REP prefix and treats REX.B PAUSE as 'xchg eax, r8d':
/* If REX_B is set, then this is xchg eax, r8d, not a nop. */
if (REX_B(s)) {
goto do_xchg_reg_eax;
}
if (prefixes & PREFIX_REPZ) {
gen_update_cc_op(s);
gen_jmp_im(s, pc_start - s->cs_base);
gen_helper_pause(cpu_env, tcg_const_i32(s->pc - pc_start));
s->base.is_jmp = DISAS_NORETURN;
}
commit 7418027ea4fec276455abd4291558bc58a0a7ba7
target-i386: fix xchg rax,r8
We were ignoring REX_B while special-casing NOP, i.e. xchg eax,eax.
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