linux-user/nios2: Fix EA vs PC confusion

The real kernel will talk about the user PC as EA,
because that's where the hardware will have copied it,
and where it expects to put it to then use ERET.
But qemu does not emulate all of the exception stuff
while emulating user-only.  Manipulate PC directly.

This fixes signal entry and return, and eliminates
some slight confusion from target_cpu_copy_regs.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20211221025012.1057923-6-richard.henderson@linaro.org>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

linux-user/nios2/cpu_loop.c

@@ -155,9 +155,6 @@ void target_cpu_copy_regs(CPUArchState *env, struct target_pt_regs *regs)
     env->regs[R_SP] = regs->sp;
     env->regs[R_GP] = regs->gp;
     env->regs[CR_ESTATUS] = regs->estatus;
-    env->regs[R_EA] = regs->ea;
-    /* TODO: unsigned long  orig_r7; */
-
-    /* Emulate eret when starting thread. */
     env->regs[R_PC] = regs->ea;
+    /* TODO: unsigned long  orig_r7; */
 }

linux-user/nios2/signal.c

@@ -73,7 +73,7 @@ static void rt_setup_ucontext(struct target_ucontext *uc, CPUNios2State *env)
     __put_user(env->regs[R_RA], &gregs[23]);
     __put_user(env->regs[R_FP], &gregs[24]);
     __put_user(env->regs[R_GP], &gregs[25]);
-    __put_user(env->regs[R_EA], &gregs[27]);
+    __put_user(env->regs[R_PC], &gregs[27]);
     __put_user(env->regs[R_SP], &gregs[28]);
 }
 
@@ -122,7 +122,7 @@ static int rt_restore_ucontext(CPUNios2State *env, struct target_ucontext *uc,
     __get_user(env->regs[R_GP], &gregs[25]);
     /* Not really necessary no user settable bits */
     __get_user(temp, &gregs[26]);
-    __get_user(env->regs[R_EA], &gregs[27]);
+    __get_user(env->regs[R_PC], &gregs[27]);
 
     __get_user(env->regs[R_RA], &gregs[23]);
     __get_user(env->regs[R_SP], &gregs[28]);
@@ -181,7 +181,7 @@ void setup_rt_frame(int sig, struct target_sigaction *ka,
     env->regs[4] = sig;
     env->regs[5] = frame_addr + offsetof(struct target_rt_sigframe, info);
     env->regs[6] = frame_addr + offsetof(struct target_rt_sigframe, uc);
-    env->regs[R_EA] = ka->_sa_handler;
+    env->regs[R_PC] = ka->_sa_handler;
 
     unlock_user_struct(frame, frame_addr, 1);
 }