hw/core: Add TCGCPUOps.record_sigbus

Add a new user-only interface for updating cpu state before
raising a signal.  This will take the place of do_unaligned_access
for user-only and should result in less boilerplate for each guest.

Reviewed-by: Warner Losh <imp@bsdimp.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

include/hw/core/tcg-cpu-ops.h

@@ -135,6 +135,29 @@ struct TCGCPUOps {
     void (*record_sigsegv)(CPUState *cpu, vaddr addr,
                            MMUAccessType access_type,
                            bool maperr, uintptr_t ra);
+    /**
+     * record_sigbus:
+     * @cpu: cpu context
+     * @addr: misaligned guest address
+     * @access_type: access was read/write/execute
+     * @ra: host pc for unwinding
+     *
+     * We are about to raise SIGBUS with si_code BUS_ADRALN,
+     * and si_addr set for @addr.  Record anything further needed
+     * for the signal ucontext_t.
+     *
+     * If the emulated kernel does not provide the signal handler with
+     * anything besides the user context registers, and the siginfo_t,
+     * then this hook need do nothing and may be omitted.
+     * Otherwise, record the data and return; the caller will raise
+     * the signal, unwind the cpu state, and return to the main loop.
+     *
+     * If it is simpler to re-use the sysemu do_unaligned_access code,
+     * @ra is provided so that a "normal" cpu exception can be raised.
+     * In this case, the signal must be raised by the architecture cpu_loop.
+     */
+    void (*record_sigbus)(CPUState *cpu, vaddr addr,
+                          MMUAccessType access_type, uintptr_t ra);
 #endif /* CONFIG_SOFTMMU */
 #endif /* NEED_CPU_H */