target/arm: Implement GCSSTR, GCSSTTR

Note that CreateAccDescGCS() does not enable tagchecked,
and Data Aborts from GCS instructions do not set iss.isv.

Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20251008215613.300150-47-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

target/arm/tcg/a64.decode

@@ -571,6 +571,9 @@ LDAPR_i         10 011001 10 0 ......... 00 ..... ..... @ldapr_stlr_i sign=1 ext
 LDAPR_i         00 011001 11 0 ......... 00 ..... ..... @ldapr_stlr_i sign=1 ext=1 sz=0
 LDAPR_i         01 011001 11 0 ......... 00 ..... ..... @ldapr_stlr_i sign=1 ext=1 sz=1
 
+# GCSSTR, GCSSTTR
+GCSSTR          11011001 000 11111 000 unpriv:1 11 rn:5 rt:5
+
 # Load/store multiple structures
 # The 4-bit opcode in [15:12] encodes repeat count and structure elements
 &ldst_mult      rm rn rt sz q p rpt selem

target/arm/tcg/translate-a64.c

@@ -139,6 +139,12 @@ static int core_a64_user_mem_index(DisasContext *s, bool unpriv)
     return arm_to_core_mmu_idx(full_a64_user_mem_index(s, unpriv));
 }
 
+/* For a given translation regime, return the core mmu_idx for gcs access. */
+static int core_gcs_mem_index(ARMMMUIdx armidx)
+{
+    return arm_to_core_mmu_idx(regime_to_gcs(armidx));
+}
+
 static void set_btype_raw(int val)
 {
     tcg_gen_st_i32(tcg_constant_i32(val), tcg_env,
@@ -3989,6 +3995,42 @@ static bool trans_STLR_i(DisasContext *s, arg_ldapr_stlr_i *a)
     return true;
 }
 
+static bool trans_GCSSTR(DisasContext *s, arg_GCSSTR *a)
+{
+    ARMMMUIdx armidx;
+
+    if (!dc_isar_feature(aa64_gcs, s)) {
+        return false;
+    }
+
+    /*
+     * The pseudocode for GCSSTTR is
+     *
+     *   effective_el = AArch64.IsUnprivAccessPriv() ? PSTATE.EL : EL0;
+     *   if (effective_el == PSTATE.EL) CheckGCSSTREnabled();
+     *
+     * We have cached the result of IsUnprivAccessPriv in DisasContext,
+     * but since we need the result of full_a64_user_mem_index anyway,
+     * use the mmu_idx test as a proxy for the effective_el test.
+     */
+    armidx = full_a64_user_mem_index(s, a->unpriv);
+    if (armidx == s->mmu_idx && s->gcsstr_el != 0) {
+        gen_exception_insn_el(s, 0, EXCP_UDEF,
+                              syn_gcs_gcsstr(a->rn, a->rt),
+                              s->gcsstr_el);
+        return true;
+    }
+
+    if (a->rn == 31) {
+        gen_check_sp_alignment(s);
+    }
+    tcg_gen_qemu_st_i64(cpu_reg(s, a->rt),
+                        clean_data_tbi(s, cpu_reg_sp(s, a->rn)),
+                        core_gcs_mem_index(armidx),
+                        finalize_memop(s, MO_64 | MO_ALIGN));
+    return true;
+}
+
 static bool trans_LD_mult(DisasContext *s, arg_ldst_mult *a)
 {
     TCGv_i64 clean_addr, tcg_rn, tcg_ebytes;