target/arm: Handle FPU check for FPCXT_NS insns via vfp_access_check_m()

Instead of open-coding the "take NOCP exception if FPU disabled,
otherwise call gen_preserve_fp_state()" code in the accessors for
FPCXT_NS, add an argument to vfp_access_check_m() which tells it to
skip the gen_update_fp_context() call, so we can use it for the
FPCXT_NS case.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210618141019.10671-8-peter.maydell@linaro.org

target/arm/translate-a32.h

@@ -32,7 +32,7 @@ bool disas_neon_shared(DisasContext *s, uint32_t insn);
 void load_reg_var(DisasContext *s, TCGv_i32 var, int reg);
 void arm_gen_condlabel(DisasContext *s);
 bool vfp_access_check(DisasContext *s);
-void gen_preserve_fp_state(DisasContext *s);
+bool vfp_access_check_m(DisasContext *s, bool skip_context_update);
 void read_neon_element32(TCGv_i32 dest, int reg, int ele, MemOp memop);
 void read_neon_element64(TCGv_i64 dest, int reg, int ele, MemOp memop);
 void write_neon_element32(TCGv_i32 src, int reg, int ele, MemOp memop);

target/arm/translate-m-nocp.c

@@ -371,17 +371,14 @@ static bool gen_M_fp_sysreg_write(DisasContext *s, int regno,
          * otherwise PreserveFPState(), and then FPCXT_NS writes
          * behave the same as FPCXT_S writes.
          */
-        if (s->fp_excp_el) {
-            gen_exception_insn(s, s->pc_curr, EXCP_NOCP,
-                               syn_uncategorized(), s->fp_excp_el);
+        if (!vfp_access_check_m(s, true)) {
             /*
              * This was only a conditional exception, so override
              * gen_exception_insn()'s default to DISAS_NORETURN
              */
             s->base.is_jmp = DISAS_NEXT;
             break;
         }
-        gen_preserve_fp_state(s);
     }
     /* fall through */
     case ARM_VFP_FPCXT_S:
@@ -527,17 +524,14 @@ static bool gen_M_fp_sysreg_read(DisasContext *s, int regno,
          * otherwise PreserveFPState(), and then FPCXT_NS
          * reads the same as FPCXT_S.
          */
-        if (s->fp_excp_el) {
-            gen_exception_insn(s, s->pc_curr, EXCP_NOCP,
-                               syn_uncategorized(), s->fp_excp_el);
+        if (!vfp_access_check_m(s, true)) {
             /*
              * This was only a conditional exception, so override
              * gen_exception_insn()'s default to DISAS_NORETURN
              */
             s->base.is_jmp = DISAS_NEXT;
             break;
         }
-        gen_preserve_fp_state(s);
         tmp = tcg_temp_new_i32();
         sfpa = tcg_temp_new_i32();
         fpscr = tcg_temp_new_i32();

target/arm/translate-vfp.c

@@ -109,7 +109,7 @@ static inline long vfp_f16_offset(unsigned reg, bool top)
  * Generate code for M-profile lazy FP state preservation if needed;
  * this corresponds to the pseudocode PreserveFPState() function.
  */
-void gen_preserve_fp_state(DisasContext *s)
+static void gen_preserve_fp_state(DisasContext *s)
 {
     if (s->v7m_lspact) {
         /*
@@ -218,8 +218,9 @@ static bool vfp_access_check_a(DisasContext *s, bool ignore_vfp_enabled)
  * If VFP is enabled, do the necessary M-profile lazy-FP handling and then
  * return true. If not, emit code to generate an appropriate exception and
  * return false.
+ * skip_context_update is true to skip the "update FP context" part of this.
  */
-static bool vfp_access_check_m(DisasContext *s)
+bool vfp_access_check_m(DisasContext *s, bool skip_context_update)
 {
     if (s->fp_excp_el) {
         /*
@@ -239,8 +240,10 @@ static bool vfp_access_check_m(DisasContext *s)
     /* Trigger lazy-state preservation if necessary */
     gen_preserve_fp_state(s);
 
-    /* Update ownership of FP context and create new FP context if needed */
-    gen_update_fp_context(s);
+    if (!skip_context_update) {
+        /* Update ownership of FP context and create new FP context if needed */
+        gen_update_fp_context(s);
+    }
 
     return true;
 }
@@ -252,7 +255,7 @@ static bool vfp_access_check_m(DisasContext *s)
 bool vfp_access_check(DisasContext *s)
 {
     if (arm_dc_feature(s, ARM_FEATURE_M)) {
-        return vfp_access_check_m(s);
+        return vfp_access_check_m(s, false);
     } else {
         return vfp_access_check_a(s, false);
     }