target/arm: Implement CLRM instruction

In v8.1M the new CLRM instruction allows zeroing an arbitrary set of
the general-purpose registers and APSR.  Implement this.

The encoding is a subset of the LDMIA T2 encoding, using what would
be Rn=0b1111 (which UNDEFs for LDMIA).

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20201119215617.29887-6-peter.maydell@linaro.org

2 files changed, 43 insertions, 1 deletions

diff --git a/target/arm/t32.decode b/target/arm/t32.decode
index cfcc71b..f045eb6 100644
--- a/target/arm/t32.decode
+++ b/target/arm/t32.decode
@@ -609,7 +609,11 @@ UXTAB            1111 1010 0101 .... 1111 .... 10.. ....      @rrr_rot
 
 STM_t32          1110 1000 10.0 .... ................         @ldstm i=1 b=0
 STM_t32          1110 1001 00.0 .... ................         @ldstm i=0 b=1
-LDM_t32          1110 1000 10.1 .... ................         @ldstm i=1 b=0
+{
+  # Rn=15 UNDEFs for LDM; M-profile CLRM uses that encoding
+  CLRM           1110 1000 1001 1111 list:16
+  LDM_t32        1110 1000 10.1 .... ................         @ldstm i=1 b=0
+}
 LDM_t32          1110 1001 00.1 .... ................         @ldstm i=0 b=1
 
 &rfe             !extern rn w pu
diff --git a/target/arm/translate.c b/target/arm/translate.c
index 9f2b601..47a1a57 100644
--- a/target/arm/translate.c
+++ b/target/arm/translate.c
@@ -7968,6 +7968,44 @@ static bool trans_LDM_t16(DisasContext *s, arg_ldst_block *a)
     return do_ldm(s, a, 1);
 }
 
+static bool trans_CLRM(DisasContext *s, arg_CLRM *a)
+{
+    int i;
+    TCGv_i32 zero;
+
+    if (!dc_isar_feature(aa32_m_sec_state, s)) {
+        return false;
+    }
+
+    if (extract32(a->list, 13, 1)) {
+        return false;
+    }
+
+    if (!a->list) {
+        /* UNPREDICTABLE; we choose to UNDEF */
+        return false;
+    }
+
+    zero = tcg_const_i32(0);
+    for (i = 0; i < 15; i++) {
+        if (extract32(a->list, i, 1)) {
+            /* Clear R[i] */
+            tcg_gen_mov_i32(cpu_R[i], zero);
+        }
+    }
+    if (extract32(a->list, 15, 1)) {
+        /*
+         * Clear APSR (by calling the MSR helper with the same argument
+         * as for "MSR APSR_nzcvqg, Rn": mask = 0b1100, SYSM=0)
+         */
+        TCGv_i32 maskreg = tcg_const_i32(0xc << 8);
+        gen_helper_v7m_msr(cpu_env, maskreg, zero);
+        tcg_temp_free_i32(maskreg);
+    }
+    tcg_temp_free_i32(zero);
+    return true;
+}
+
 /*
  * Branch, branch with link
  */