[Qemu-devel] [PATCH 10/26] target/arm: Handle floating point registers in exception entry

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

Handle floating point registers in exception entry.
This corresponds to the FP-specific parts of the pseudocode
functions ActivateException() and PushStack().

We defer the code corresponding to UpdateFPCCR() to a later patch.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 target/arm/helper.c | 98 +++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 95 insertions(+), 3 deletions(-)

diff --git a/target/arm/helper.c b/target/arm/helper.c
index a2222f84803..7b2174a5e61 100644
--- a/target/arm/helper.c
+++ b/target/arm/helper.c
@@ -8172,6 +8172,9 @@ static void v7m_exception_taken(ARMCPU *cpu, uint32_t lr, bool dotailchain,
     switch_v7m_security_state(env, targets_secure);
     write_v7m_control_spsel(env, 0);
     arm_clear_exclusive(env);
+    /* Clear SFPA and FPCA (has no effect if no FPU) */
+    env->v7m.control[M_REG_S] &=
+        ~(R_V7M_CONTROL_FPCA_MASK | R_V7M_CONTROL_SFPA_MASK);
     /* Clear IT bits */
     env->condexec_bits = 0;
     env->regs[14] = lr;
@@ -8192,6 +8195,20 @@ static bool v7m_push_stack(ARMCPU *cpu)
     uint32_t xpsr = xpsr_read(env);
     uint32_t frameptr = env->regs[13];
     ARMMMUIdx mmu_idx = arm_mmu_idx(env);
+    uint32_t framesize;
+    bool nsacr_cp10 = extract32(env->v7m.nsacr, 10, 1);
+
+    if ((env->v7m.control[M_REG_S] & R_V7M_CONTROL_FPCA_MASK) &&
+        (env->v7m.secure || nsacr_cp10)) {
+        if (env->v7m.secure &&
+            env->v7m.fpccr[M_REG_S] & R_V7M_FPCCR_TS_MASK) {
+            framesize = 0xa8;
+        } else {
+            framesize = 0x68;
+        }
+    } else {
+        framesize = 0x20;
+    }
 
     /* Align stack pointer if the guest wants that */
     if ((frameptr & 4) &&
@@ -8200,7 +8217,13 @@ static bool v7m_push_stack(ARMCPU *cpu)
         xpsr |= XPSR_SPREALIGN;
     }
 
-    frameptr -= 0x20;
+    xpsr &= ~XPSR_SFPA;
+    if (env->v7m.secure &&
+        (env->v7m.control[M_REG_S] & R_V7M_CONTROL_SFPA_MASK)) {
+        xpsr |= XPSR_SFPA;
+    }
+
+    frameptr -= framesize;
 
     if (arm_feature(env, ARM_FEATURE_V8)) {
         uint32_t limit = v7m_sp_limit(env);
@@ -8244,6 +8267,73 @@ static bool v7m_push_stack(ARMCPU *cpu)
         v7m_stack_write(cpu, frameptr + 24, env->regs[15], mmu_idx, false) &&
         v7m_stack_write(cpu, frameptr + 28, xpsr, mmu_idx, false);
 
+    if (env->v7m.control[M_REG_S] & R_V7M_CONTROL_FPCA_MASK) {
+        /* FPU is active, try to save its registers */
+        bool fpccr_s = env->v7m.fpccr[M_REG_S] & R_V7M_FPCCR_S_MASK;
+        bool lspact = env->v7m.fpccr[fpccr_s] & R_V7M_FPCCR_LSPACT_MASK;
+
+        if (lspact && arm_feature(env, ARM_FEATURE_M_SECURITY)) {
+            qemu_log_mask(CPU_LOG_INT,
+                          "...SecureFault because LSPACT and FPCA both set\n");
+            env->v7m.sfsr |= R_V7M_SFSR_LSERR_MASK;
+            armv7m_nvic_set_pending(env->nvic, ARMV7M_EXCP_SECURE, false);
+        } else if (!env->v7m.secure && !nsacr_cp10) {
+            qemu_log_mask(CPU_LOG_INT,
+                          "...Secure UsageFault with CFSR.NOCP because "
+                          "NSACR.CP10 prevents stacking FP regs\n");
+            armv7m_nvic_set_pending(env->nvic, ARMV7M_EXCP_USAGE, M_REG_S);
+            env->v7m.cfsr[M_REG_S] |= R_V7M_CFSR_NOCP_MASK;
+        } else {
+            if (!(env->v7m.fpccr[M_REG_S] & R_V7M_FPCCR_LSPEN_MASK)) {
+                /* Lazy stacking disabled, save registers now */
+                int i;
+                bool cpacr_pass = v7m_cpacr_pass(env, env->v7m.secure,
+                                                 arm_current_el(env) != 0);
+
+                if (stacked_ok && !cpacr_pass) {
+                    /*
+                     * Take UsageFault if CPACR forbids access. The pseudocode
+                     * here does a full CheckCPEnabled() but we know the NSACR
+                     * check can never fail as we have already handled that.
+                     */
+                    qemu_log_mask(CPU_LOG_INT,
+                                  "...UsageFault with CFSR.NOCP because "
+                                  "CPACR.CP10 prevents stacking FP regs\n");
+                    armv7m_nvic_set_pending(env->nvic, ARMV7M_EXCP_USAGE,
+                                            env->v7m.secure);
+                    env->v7m.cfsr[env->v7m.secure] |= R_V7M_CFSR_NOCP_MASK;
+                    stacked_ok = false;
+                }
+
+                for (i = 0; i < ((framesize == 0xa8) ? 32 : 16); i += 2) {
+                    uint64_t dn = *aa32_vfp_dreg(env, i / 2);
+                    uint32_t faddr = frameptr + 0x20 + 4 * i;
+                    uint32_t slo = extract64(dn, 0, 32);
+                    uint32_t shi = extract64(dn, 32, 32);
+
+                    if (i >= 16) {
+                        faddr += 8; /* skip the slot for the FPSCR */
+                    }
+                    stacked_ok = stacked_ok &&
+                        v7m_stack_write(cpu, faddr, slo, mmu_idx, false) &&
+                        v7m_stack_write(cpu, faddr + 4, shi, mmu_idx, false);
+                }
+                stacked_ok = stacked_ok &&
+                    v7m_stack_write(cpu, frameptr + 0x60,
+                                    vfp_get_fpscr(env), mmu_idx, false);
+                if (cpacr_pass) {
+                    for (i = 0; i < ((framesize == 0xa8) ? 32 : 16); i += 2) {
+                        *aa32_vfp_dreg(env, i / 2) = 0;
+                    }
+                    vfp_set_fpscr(env, 0);
+                }
+            } else {
+                /* Lazy stacking enabled, save necessary info to stack later */
+                /* TODO : equivalent of UpdateFPCCR() pseudocode */
+            }
+        }
+    }
+
     /*
      * If we broke a stack limit then SP was already updated earlier;
      * otherwise we update SP regardless of whether any of the stack
@@ -9004,8 +9094,7 @@ void arm_v7m_cpu_do_interrupt(CPUState *cs)
 
     if (arm_feature(env, ARM_FEATURE_V8)) {
         lr = R_V7M_EXCRET_RES1_MASK |
-            R_V7M_EXCRET_DCRS_MASK |
-            R_V7M_EXCRET_FTYPE_MASK;
+            R_V7M_EXCRET_DCRS_MASK;
         /* The S bit indicates whether we should return to Secure
          * or NonSecure (ie our current state).
          * The ES bit indicates whether we're taking this exception
@@ -9020,6 +9109,9 @@ void arm_v7m_cpu_do_interrupt(CPUState *cs)
         if (env->v7m.secure) {
             lr |= R_V7M_EXCRET_S_MASK;
         }
+        if (!(env->v7m.control[M_REG_S] & R_V7M_CONTROL_FPCA_MASK)) {
+            lr |= R_V7M_EXCRET_FTYPE_MASK;
+        }
     } else {
         lr = R_V7M_EXCRET_RES1_MASK |
             R_V7M_EXCRET_S_MASK |
-- 
2.20.1