linux-user: Reorg handling for SIGSEGV

Add stub host-signal.h for all linux-user hosts.
Add new code replacing cpu_signal_handler.
Full migration will happen one host at a time.

Reviewed-by: Warner Losh <imp@bsdimp.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

linux-user/host/aarch64/host-signal.h

@@ -0,0 +1 @@
+#define HOST_SIGNAL_PLACEHOLDER

linux-user/host/arm/host-signal.h

@@ -0,0 +1 @@
+#define HOST_SIGNAL_PLACEHOLDER

linux-user/host/i386/host-signal.h

@@ -0,0 +1 @@
+#define HOST_SIGNAL_PLACEHOLDER

linux-user/host/mips/host-signal.h

@@ -0,0 +1 @@
+#define HOST_SIGNAL_PLACEHOLDER

linux-user/host/ppc/host-signal.h

@@ -0,0 +1 @@
+#define HOST_SIGNAL_PLACEHOLDER

linux-user/host/ppc64/host-signal.h

@@ -0,0 +1 @@
+#define HOST_SIGNAL_PLACEHOLDER

linux-user/host/riscv/host-signal.h

@@ -0,0 +1 @@
+#define HOST_SIGNAL_PLACEHOLDER

linux-user/host/s390/host-signal.h

@@ -0,0 +1 @@
+#define HOST_SIGNAL_PLACEHOLDER

linux-user/host/s390x/host-signal.h

@@ -0,0 +1 @@
+#define HOST_SIGNAL_PLACEHOLDER

linux-user/host/sparc/host-signal.h

@@ -0,0 +1 @@
+#define HOST_SIGNAL_PLACEHOLDER

linux-user/host/sparc64/host-signal.h

@@ -0,0 +1 @@
+#define HOST_SIGNAL_PLACEHOLDER

linux-user/host/x32/host-signal.h

@@ -0,0 +1 @@
+#define HOST_SIGNAL_PLACEHOLDER

linux-user/host/x86_64/host-signal.h

@@ -0,0 +1 @@
+#define HOST_SIGNAL_PLACEHOLDER

linux-user/signal.c

@@ -19,6 +19,7 @@
 #include "qemu/osdep.h"
 #include "qemu/bitops.h"
 #include "exec/gdbstub.h"
+#include "hw/core/tcg-cpu-ops.h"
 
 #include <sys/ucontext.h>
 #include <sys/resource.h>
@@ -29,6 +30,7 @@
 #include "loader.h"
 #include "trace.h"
 #include "signal-common.h"
+#include "host-signal.h"
 
 static struct target_sigaction sigact_table[TARGET_NSIG];
 
@@ -769,41 +771,116 @@ static inline void rewind_if_in_safe_syscall(void *puc)
 }
 #endif
 
-static void host_signal_handler(int host_signum, siginfo_t *info,
+static void host_signal_handler(int host_sig, siginfo_t *info, void *puc)
-                                void *puc)
 {
     CPUArchState *env = thread_cpu->env_ptr;
     CPUState *cpu = env_cpu(env);
     TaskState *ts = cpu->opaque;
-
-    int sig;
     target_siginfo_t tinfo;
     ucontext_t *uc = puc;
     struct emulated_sigtable *k;
+    int guest_sig;
 
+#ifdef HOST_SIGNAL_PLACEHOLDER
     /* the CPU emulator uses some host signals to detect exceptions,
        we forward to it some signals */
-    if ((host_signum == SIGSEGV || host_signum == SIGBUS)
+    if ((host_sig == SIGSEGV || host_sig == SIGBUS)
         && info->si_code > 0) {
-        if (cpu_signal_handler(host_signum, info, puc))
+        if (cpu_signal_handler(host_sig, info, puc)) {
+            return;
+        }
+    }
+#else
+    uintptr_t pc = 0;
+    bool sync_sig = false;
+
+    /*
+     * Non-spoofed SIGSEGV and SIGBUS are synchronous, and need special
+     * handling wrt signal blocking and unwinding.
+     */
+    if ((host_sig == SIGSEGV || host_sig == SIGBUS) && info->si_code > 0) {
+        MMUAccessType access_type;
+        uintptr_t host_addr;
+        abi_ptr guest_addr;
+        bool is_write;
+
+        host_addr = (uintptr_t)info->si_addr;
+
+        /*
+         * Convert forcefully to guest address space: addresses outside
+         * reserved_va are still valid to report via SEGV_MAPERR.
+         */
+        guest_addr = h2g_nocheck(host_addr);
+
+        pc = host_signal_pc(uc);
+        is_write = host_signal_write(info, uc);
+        access_type = adjust_signal_pc(&pc, is_write);
+
+        if (host_sig == SIGSEGV) {
+            const struct TCGCPUOps *tcg_ops;
+
+            if (info->si_code == SEGV_ACCERR && h2g_valid(host_addr)) {
+                /* If this was a write to a TB protected page, restart. */
+                if (is_write &&
+                    handle_sigsegv_accerr_write(cpu, &uc->uc_sigmask,
+                                                pc, guest_addr)) {
                     return;
                 }
 
+                /*
+                 * With reserved_va, the whole address space is PROT_NONE,
+                 * which means that we may get ACCERR when we want MAPERR.
+                 */
+                if (page_get_flags(guest_addr) & PAGE_VALID) {
+                    /* maperr = false; */
+                } else {
+                    info->si_code = SEGV_MAPERR;
+                }
+            }
+
+            sigprocmask(SIG_SETMASK, &uc->uc_sigmask, NULL);
+
+            tcg_ops = CPU_GET_CLASS(cpu)->tcg_ops;
+            tcg_ops->tlb_fill(cpu, guest_addr, 0, access_type,
+                              MMU_USER_IDX, false, pc);
+            g_assert_not_reached();
+        } else {
+            sigprocmask(SIG_SETMASK, &uc->uc_sigmask, NULL);
+        }
+
+        sync_sig = true;
+    }
+#endif
+
     /* get target signal number */
-    sig = host_to_target_signal(host_signum);
+    guest_sig = host_to_target_signal(host_sig);
-    if (sig < 1 || sig > TARGET_NSIG)
+    if (guest_sig < 1 || guest_sig > TARGET_NSIG) {
         return;
-    trace_user_host_signal(env, host_signum, sig);
+    }
+    trace_user_host_signal(env, host_sig, guest_sig);
+
+    host_to_target_siginfo_noswap(&tinfo, info);
+    k = &ts->sigtab[guest_sig - 1];
+    k->info = tinfo;
+    k->pending = guest_sig;
+    ts->signal_pending = 1;
+
+#ifndef HOST_SIGNAL_PLACEHOLDER
+    /*
+     * For synchronous signals, unwind the cpu state to the faulting
+     * insn and then exit back to the main loop so that the signal
+     * is delivered immediately.
+     */
+    if (sync_sig) {
+        cpu->exception_index = EXCP_INTERRUPT;
+        cpu_loop_exit_restore(cpu, pc);
+    }
+#endif
 
     rewind_if_in_safe_syscall(puc);
 
-    host_to_target_siginfo_noswap(&tinfo, info);
+    /*
-    k = &ts->sigtab[sig - 1];
+     * Block host signals until target signal handler entered. We
-    k->info = tinfo;
-    k->pending = sig;
-    ts->signal_pending = 1;
-
-    /* Block host signals until target signal handler entered. We
      * can't block SIGSEGV or SIGBUS while we're executing guest
      * code in case the guest code provokes one in the window between
      * now and it getting out to the main loop. Signals will be