[Qemu-devel] [PATCH v6 09/37] target-arm: Fix VFP enables for AArch32 EL0 under AArch64 EL1

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

The current A32/T32 decoder bases its "is VFP/Neon enabled?" check
on the FPSCR.EN bit. This is correct if EL1 is AArch32, but for
an AArch64 EL1 the logic is different: it must act as if FPSCR.EN
is always set. Instead, trapping must happen according to CPACR
bits for cp10/cp11; these cover all of FP/Neon, including the
FPSCR/FPSID/MVFR register accesses which FPSCR.EN does not affect.
Add support for CPACR checks (which are also required for ARMv7,
but were unimplemented because Linux happens not to use them)
and make sure they generate exceptions with the correct syndrome.

We actually return incorrect syndrome information for cases
where FP is disabled but the specific instruction bit pattern
is unallocated: strictly these should be the Uncategorized
exception, not a "SIMD disabled" exception. This should be
mostly harmless, and the structure of the A32/T32 VFP/Neon
decoder makes it painful to put the 'FP disabled?' checks in
the right places.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
---
 target-arm/cpu.h       | 10 +++++++++-
 target-arm/translate.c | 31 +++++++++++++++++++++++++++++++
 2 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/target-arm/cpu.h b/target-arm/cpu.h
index 72c4c7a..ff56519 100644
--- a/target-arm/cpu.h
+++ b/target-arm/cpu.h
@@ -1104,6 +1104,8 @@ static inline int cpu_mmu_index (CPUARMState *env)
 #define ARM_TBFLAG_CONDEXEC_MASK    (0xff << ARM_TBFLAG_CONDEXEC_SHIFT)
 #define ARM_TBFLAG_BSWAP_CODE_SHIFT 16
 #define ARM_TBFLAG_BSWAP_CODE_MASK  (1 << ARM_TBFLAG_BSWAP_CODE_SHIFT)
+#define ARM_TBFLAG_CPACR_FPEN_SHIFT 17
+#define ARM_TBFLAG_CPACR_FPEN_MASK  (1 << ARM_TBFLAG_CPACR_FPEN_SHIFT)
 
 /* Bit usage when in AArch64 state */
 #define ARM_TBFLAG_AA64_EL_SHIFT    0
@@ -1128,6 +1130,8 @@ static inline int cpu_mmu_index (CPUARMState *env)
     (((F) & ARM_TBFLAG_CONDEXEC_MASK) >> ARM_TBFLAG_CONDEXEC_SHIFT)
 #define ARM_TBFLAG_BSWAP_CODE(F) \
     (((F) & ARM_TBFLAG_BSWAP_CODE_MASK) >> ARM_TBFLAG_BSWAP_CODE_SHIFT)
+#define ARM_TBFLAG_CPACR_FPEN(F) \
+    (((F) & ARM_TBFLAG_CPACR_FPEN_MASK) >> ARM_TBFLAG_CPACR_FPEN_SHIFT)
 #define ARM_TBFLAG_AA64_EL(F) \
     (((F) & ARM_TBFLAG_AA64_EL_MASK) >> ARM_TBFLAG_AA64_EL_SHIFT)
 #define ARM_TBFLAG_AA64_FPEN(F) \
@@ -1161,9 +1165,13 @@ static inline void cpu_get_tb_cpu_state(CPUARMState *env, target_ulong *pc,
         if (privmode) {
             *flags |= ARM_TBFLAG_PRIV_MASK;
         }
-        if (env->vfp.xregs[ARM_VFP_FPEXC] & (1 << 30)) {
+        if (env->vfp.xregs[ARM_VFP_FPEXC] & (1 << 30)
+            || arm_el_is_aa64(env, 1)) {
             *flags |= ARM_TBFLAG_VFPEN_MASK;
         }
+        if (fpen == 3 || (fpen == 1 && arm_current_pl(env) != 0)) {
+            *flags |= ARM_TBFLAG_CPACR_FPEN_MASK;
+        }
     }
 
     *cs_base = 0;
diff --git a/target-arm/translate.c b/target-arm/translate.c
index 84700ca..03e2c00 100644
--- a/target-arm/translate.c
+++ b/target-arm/translate.c
@@ -2952,6 +2952,16 @@ static int disas_vfp_insn(CPUARMState * env, DisasContext *s, uint32_t insn)
     if (!arm_feature(env, ARM_FEATURE_VFP))
         return 1;
 
+    /* FIXME: this access check should not take precedence over UNDEF
+     * for invalid encodings; we will generate incorrect syndrome information
+     * for attempts to execute invalid vfp/neon encodings with FP disabled.
+     */
+    if (!s->cpacr_fpen) {
+        gen_exception_insn(s, 4, EXCP_UDEF,
+                           syn_fp_access_trap(1, 0xe, s->thumb));
+        return 0;
+    }
+
     if (!s->vfp_enabled) {
         /* VFP disabled.  Only allow fmxr/fmrx to/from some control regs.  */
         if ((insn & 0x0fe00fff) != 0x0ee00a10)
@@ -4232,6 +4242,16 @@ static int disas_neon_ls_insn(CPUARMState * env, DisasContext *s, uint32_t insn)
     TCGv_i32 tmp2;
     TCGv_i64 tmp64;
 
+    /* FIXME: this access check should not take precedence over UNDEF
+     * for invalid encodings; we will generate incorrect syndrome information
+     * for attempts to execute invalid vfp/neon encodings with FP disabled.
+     */
+    if (!s->cpacr_fpen) {
+        gen_exception_insn(s, 4, EXCP_UDEF,
+                           syn_fp_access_trap(1, 0xe, s->thumb));
+        return 0;
+    }
+
     if (!s->vfp_enabled)
       return 1;
     VFP_DREG_D(rd, insn);
@@ -4954,6 +4974,16 @@ static int disas_neon_data_insn(CPUARMState * env, DisasContext *s, uint32_t ins
     TCGv_i32 tmp, tmp2, tmp3, tmp4, tmp5;
     TCGv_i64 tmp64;
 
+    /* FIXME: this access check should not take precedence over UNDEF
+     * for invalid encodings; we will generate incorrect syndrome information
+     * for attempts to execute invalid vfp/neon encodings with FP disabled.
+     */
+    if (!s->cpacr_fpen) {
+        gen_exception_insn(s, 4, EXCP_UDEF,
+                           syn_fp_access_trap(1, 0xe, s->thumb));
+        return 0;
+    }
+
     if (!s->vfp_enabled)
       return 1;
     q = (insn & (1 << 6)) != 0;
@@ -10736,6 +10766,7 @@ static inline void gen_intermediate_code_internal(ARMCPU *cpu,
 #if !defined(CONFIG_USER_ONLY)
     dc->user = (ARM_TBFLAG_PRIV(tb->flags) == 0);
 #endif
+    dc->cpacr_fpen = ARM_TBFLAG_CPACR_FPEN(tb->flags);
     dc->vfp_enabled = ARM_TBFLAG_VFPEN(tb->flags);
     dc->vec_len = ARM_TBFLAG_VECLEN(tb->flags);
     dc->vec_stride = ARM_TBFLAG_VECSTRIDE(tb->flags);
-- 
1.9.1