[Qemu-devel] [PATCH 17/26] target/arm: Overlap VECSTRIDE and XSCALE_CPAR TB flags

[Peter Maydell <peter.maydell@linaro.org>]

We are close to running out of TB flags for AArch32; we could
start using the cs_base word, but before we do that we can
economise on our usage by sharing the same bits for the VFP
VECSTRIDE field and the XScale XSCALE_CPAR field. This
works because no XScale CPU ever had VFP.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 target/arm/cpu.h       | 10 ++++++----
 target/arm/cpu.c       |  7 +++++++
 target/arm/helper.c    |  6 +++++-
 target/arm/translate.c |  9 +++++++--
 4 files changed, 25 insertions(+), 7 deletions(-)

diff --git a/target/arm/cpu.h b/target/arm/cpu.h
index c436f628987..a4e4d17e787 100644
--- a/target/arm/cpu.h
+++ b/target/arm/cpu.h
@@ -3139,6 +3139,12 @@ FIELD(TBFLAG_ANY, BE_DATA, 23, 1)
 FIELD(TBFLAG_A32, THUMB, 0, 1)
 FIELD(TBFLAG_A32, VECLEN, 1, 3)
 FIELD(TBFLAG_A32, VECSTRIDE, 4, 2)
+/*
+ * We store the bottom two bits of the CPAR as TB flags and handle
+ * checks on the other bits at runtime. This shares the same bits as
+ * VECSTRIDE, which is OK as no XScale CPU has VFP.
+ */
+FIELD(TBFLAG_A32, XSCALE_CPAR, 4, 2)
 /*
  * Indicates whether cp register reads and writes by guest code should access
  * the secure or nonsecure bank of banked registers; note that this is not
@@ -3148,10 +3154,6 @@ FIELD(TBFLAG_A32, NS, 6, 1)
 FIELD(TBFLAG_A32, VFPEN, 7, 1)
 FIELD(TBFLAG_A32, CONDEXEC, 8, 8)
 FIELD(TBFLAG_A32, SCTLR_B, 16, 1)
-/* We store the bottom two bits of the CPAR as TB flags and handle
- * checks on the other bits at runtime
- */
-FIELD(TBFLAG_A32, XSCALE_CPAR, 17, 2)
 /* For M profile only, Handler (ie not Thread) mode */
 FIELD(TBFLAG_A32, HANDLER, 21, 1)
 /* For M profile only, whether we should generate stack-limit checks */
diff --git a/target/arm/cpu.c b/target/arm/cpu.c
index 3f9c81e7e9e..dd6c4f6da8d 100644
--- a/target/arm/cpu.c
+++ b/target/arm/cpu.c
@@ -1035,6 +1035,13 @@ static void arm_cpu_realizefn(DeviceState *dev, Error **errp)
         set_feature(env, ARM_FEATURE_THUMB_DSP);
     }
 
+    /*
+     * We rely on no XScale CPU having VFP so we can use the same bits in the
+     * TB flags field for VECSTRIDE and XSCALE_CPAR.
+     */
+    assert(!(arm_feature(env, ARM_FEATURE_VFP) &&
+             arm_feature(env, ARM_FEATURE_XSCALE)));
+
     if (arm_feature(env, ARM_FEATURE_V7) &&
         !arm_feature(env, ARM_FEATURE_M) &&
         !arm_feature(env, ARM_FEATURE_PMSA)) {
diff --git a/target/arm/helper.c b/target/arm/helper.c
index 0c5b0a73e95..d8a9620b870 100644
--- a/target/arm/helper.c
+++ b/target/arm/helper.c
@@ -13375,7 +13375,11 @@ void cpu_get_tb_cpu_state(CPUARMState *env, target_ulong *pc,
             || arm_el_is_aa64(env, 1) || arm_feature(env, ARM_FEATURE_M)) {
             flags = FIELD_DP32(flags, TBFLAG_A32, VFPEN, 1);
         }
-        flags = FIELD_DP32(flags, TBFLAG_A32, XSCALE_CPAR, env->cp15.c15_cpar);
+        /* Note that XSCALE_CPAR shares bits with VECSTRIDE */
+        if (arm_feature(env, ARM_FEATURE_XSCALE)) {
+            flags = FIELD_DP32(flags, TBFLAG_A32,
+                               XSCALE_CPAR, env->cp15.c15_cpar);
+        }
     }
 
     flags = FIELD_DP32(flags, TBFLAG_ANY, MMUIDX, arm_to_core_mmu_idx(mmu_idx));
diff --git a/target/arm/translate.c b/target/arm/translate.c
index d280b3a9a3a..9172a382c4d 100644
--- a/target/arm/translate.c
+++ b/target/arm/translate.c
@@ -13329,8 +13329,13 @@ static void arm_tr_init_disas_context(DisasContextBase *dcbase, CPUState *cs)
     dc->fp_excp_el = FIELD_EX32(tb_flags, TBFLAG_ANY, FPEXC_EL);
     dc->vfp_enabled = FIELD_EX32(tb_flags, TBFLAG_A32, VFPEN);
     dc->vec_len = FIELD_EX32(tb_flags, TBFLAG_A32, VECLEN);
-    dc->vec_stride = FIELD_EX32(tb_flags, TBFLAG_A32, VECSTRIDE);
-    dc->c15_cpar = FIELD_EX32(tb_flags, TBFLAG_A32, XSCALE_CPAR);
+    if (arm_feature(env, ARM_FEATURE_XSCALE)) {
+        dc->c15_cpar = FIELD_EX32(tb_flags, TBFLAG_A32, XSCALE_CPAR);
+        dc->vec_stride = 0;
+    } else {
+        dc->vec_stride = FIELD_EX32(tb_flags, TBFLAG_A32, VECSTRIDE);
+        dc->c15_cpar = 0;
+    }
     dc->v7m_handler_mode = FIELD_EX32(tb_flags, TBFLAG_A32, HANDLER);
     dc->v8m_secure = arm_feature(env, ARM_FEATURE_M_SECURITY) &&
         regime_is_secure(env, dc->mmu_idx);
-- 
2.20.1