target/s390x: Tidy SRST

Since we require all registers saved on input, read R0 from ENV instead
of passing it manually.  Recognize the specification exception when R0
contains incorrect data.  Keep high bits of result registers unmodified
when in 31 or 24-bit mode.
Reviewed-by: NAurelien Jarno <aurelien@aurel32.net>
Signed-off-by: NRichard Henderson <rth@twiddle.net>

target/s390x/helper.h

@@ -12,7 +12,7 @@ DEF_HELPER_FLAGS_3(divs32, TCG_CALL_NO_WG, s64, env, s64, s64)
 DEF_HELPER_FLAGS_3(divu32, TCG_CALL_NO_WG, i64, env, i64, i64)
 DEF_HELPER_FLAGS_3(divs64, TCG_CALL_NO_WG, s64, env, s64, s64)
 DEF_HELPER_FLAGS_4(divu64, TCG_CALL_NO_WG, i64, env, i64, i64, i64)
-DEF_HELPER_4(srst, i64, env, i64, i64, i64)
+DEF_HELPER_3(srst, void, env, i32, i32)
 DEF_HELPER_4(clst, i64, env, i64, i64, i64)
 DEF_HELPER_FLAGS_4(mvn, TCG_CALL_NO_WG, void, env, i32, i64, i64)
 DEF_HELPER_FLAGS_4(mvo, TCG_CALL_NO_WG, void, env, i32, i64, i64)

target/s390x/insn-data.def

@@ -736,7 +736,7 @@
     C(0xec57, RXSBG,   RIE_f, GIE, 0, r2, r1, 0, rosbg, 0)
 
 /* SEARCH STRING */
-    C(0xb25e, SRST,    RRE,   Z,   r1_o, r2_o, 0, 0, srst, 0)
+    C(0xb25e, SRST,    RRE,   Z,   0, 0, 0, 0, srst, 0)
 
 /* SET ACCESS */
     C(0xb24e, SAR,     RRE,   Z,   0, r2_o, 0, 0, sar, 0)

target/s390x/mem_helper.c

@@ -538,18 +538,21 @@ static inline void set_length(CPUS390XState *env, int reg, uint64_t length)
 }
 
 /* search string (c is byte to search, r2 is string, r1 end of string) */
-uint64_t HELPER(srst)(CPUS390XState *env, uint64_t r0, uint64_t end,
-                      uint64_t str)
+void HELPER(srst)(CPUS390XState *env, uint32_t r1, uint32_t r2)
 {
     uintptr_t ra = GETPC();
+    uint64_t end, str;
     uint32_t len;
-    uint8_t v, c = r0;
+    uint8_t v, c = env->regs[0];
 
-    str = wrap_address(env, str);
-    end = wrap_address(env, end);
+    /* Bits 32-55 must contain all 0.  */
+    if (env->regs[0] & 0xffffff00u) {
+        cpu_restore_state(ENV_GET_CPU(env), ra);
+        program_interrupt(env, PGM_SPECIFICATION, 6);
+    }
 
-    /* Assume for now that R2 is unmodified.  */
-    env->retxl = str;
+    str = get_address(env, r2);
+    end = get_address(env, r1);
 
     /* Lest we fail to service interrupts in a timely manner, limit the
        amount of work we're willing to do.  For now, let's cap at 8k.  */
@@ -557,20 +560,20 @@ uint64_t HELPER(srst)(CPUS390XState *env, uint64_t r0, uint64_t end,
         if (str + len == end) {
             /* Character not found.  R1 & R2 are unmodified.  */
             env->cc_op = 2;
-            return end;
+            return;
         }
         v = cpu_ldub_data_ra(env, str + len, ra);
         if (v == c) {
             /* Character found.  Set R1 to the location; R2 is unmodified.  */
             env->cc_op = 1;
-            return str + len;
+            set_address(env, r1, str + len);
+            return;
         }
     }
 
     /* CPU-determined bytes processed.  Advance R2 to next byte to process.  */
-    env->retxl = str + len;
     env->cc_op = 3;
-    return end;
+    set_address(env, r2, str + len);
 }
 
 /* unsigned string compare (c is string terminator) */

target/s390x/translate.c

@@ -4287,9 +4287,14 @@ static ExitStatus op_stpq(DisasContext *s, DisasOps *o)
 
 static ExitStatus op_srst(DisasContext *s, DisasOps *o)
 {
-    gen_helper_srst(o->in1, cpu_env, regs[0], o->in1, o->in2);
+    TCGv_i32 r1 = tcg_const_i32(get_field(s->fields, r1));
+    TCGv_i32 r2 = tcg_const_i32(get_field(s->fields, r2));
+
+    gen_helper_srst(cpu_env, r1, r2);
+
+    tcg_temp_free_i32(r1);
+    tcg_temp_free_i32(r2);
     set_cc_static(s);
-    return_low128(o->in2);
     return NO_EXIT;
 }