linux-user/signal.c: Create a common rewind_if_in_safe_syscall

All instances of rewind_if_in_safe_syscall are the same, differing only
in how the instruction point is fetched from the ucontext and the size
of the registers. Use host_signal_pc and new host_signal_set_pc
interfaces to fetch the pointer to the PC and adjust if needed. Delete
all the old copies of rewind_if_in_safe_syscall.

Acked-by: Laurent Vivier <laurent@vivier.eu>
Signed-off-by: Warner Losh <imp@bsdimp.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20211113045603.60391-3-imp@bsdimp.com>
[rth: include safe-syscall.h, simplify ifdefs]
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

linux-user/signal.c

@@ -31,6 +31,7 @@
 #include "trace.h"
 #include "signal-common.h"
 #include "host-signal.h"
+#include "safe-syscall.h"
 
 static struct target_sigaction sigact_table[TARGET_NSIG];
 
@@ -793,12 +794,20 @@ int queue_signal(CPUArchState *env, int sig, int si_type,
     return 1; /* indicates that the signal was queued */
 }
 
-#ifndef HAVE_SAFE_SYSCALL
+
+/* Adjust the signal context to rewind out of safe-syscall if we're in it */
 static inline void rewind_if_in_safe_syscall(void *puc)
 {
-    /* Default version: never rewind */
-}
+#ifdef HAVE_SAFE_SYSCALL
+    ucontext_t *uc = (ucontext_t *)puc;
+    uintptr_t pcreg = host_signal_pc(uc);
+
+    if (pcreg > (uintptr_t)safe_syscall_start
+        && pcreg < (uintptr_t)safe_syscall_end) {
+        host_signal_set_pc(uc, (uintptr_t)safe_syscall_start);
+    }
 #endif
+}
 
 static void host_signal_handler(int host_sig, siginfo_t *info, void *puc)
 {