[PATCH v2 1/8] target/arm: Take an exception if PSTATE.IL is set

[Richard Henderson <richard.henderson@linaro.org>]

From: Peter Maydell <peter.maydell@linaro.org>

In v8A, the PSTATE.IL bit is set for various kinds of illegal
exception return or mode-change attempts.  We already set PSTATE.IL
(or its AArch32 equivalent CPSR.IL) in all those cases, but we
weren't implementing the part of the behaviour where attempting to
execute an instruction with PSTATE.IL takes an immediate exception
with an appropriate syndrome value.

Add a new TB flags bit tracking PSTATE.IL/CPSR.IL, and generate code
to take an exception instead of whatever the instruction would have
been.

PSTATE.IL and CPSR.IL change only on exception entry, attempted
exception exit, and various AArch32 mode changes via cpsr_write().
These places generally already rebuild the hflags, so the only place
we need an extra rebuild_hflags call is in the illegal-return
codepath of the AArch64 exception_return helper.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-Id: <20210817162118.24319-1-peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
[rth: Added missing returns; set IL bit in syndrome]
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 target/arm/cpu.h           |  1 +
 target/arm/syndrome.h      |  5 +++++
 target/arm/translate.h     |  2 ++
 target/arm/helper-a64.c    |  1 +
 target/arm/helper.c        |  8 ++++++++
 target/arm/translate-a64.c | 11 +++++++++++
 target/arm/translate.c     | 21 +++++++++++++++++++++
 7 files changed, 49 insertions(+)

diff --git a/target/arm/cpu.h b/target/arm/cpu.h
index 9f0a5f84d5..be557bf5d8 100644
--- a/target/arm/cpu.h
+++ b/target/arm/cpu.h
@@ -3441,6 +3441,7 @@ FIELD(TBFLAG_ANY, FPEXC_EL, 8, 2)
 FIELD(TBFLAG_ANY, DEBUG_TARGET_EL, 10, 2)
 /* Memory operations require alignment: SCTLR_ELx.A or CCR.UNALIGN_TRP */
 FIELD(TBFLAG_ANY, ALIGN_MEM, 12, 1)
+FIELD(TBFLAG_ANY, PSTATE__IL, 13, 1)
 
 /*
  * Bit usage when in AArch32 state, both A- and M-profile.
diff --git a/target/arm/syndrome.h b/target/arm/syndrome.h
index 39a31260f2..54d135897b 100644
--- a/target/arm/syndrome.h
+++ b/target/arm/syndrome.h
@@ -270,4 +270,9 @@ static inline uint32_t syn_wfx(int cv, int cond, int ti, bool is_16bit)
            (cv << 24) | (cond << 20) | ti;
 }
 
+static inline uint32_t syn_illegalstate(void)
+{
+    return (EC_ILLEGALSTATE << ARM_EL_EC_SHIFT) | ARM_EL_IL;
+}
+
 #endif /* TARGET_ARM_SYNDROME_H */
diff --git a/target/arm/translate.h b/target/arm/translate.h
index 241596c5bd..af1b6fa03c 100644
--- a/target/arm/translate.h
+++ b/target/arm/translate.h
@@ -98,6 +98,8 @@ typedef struct DisasContext {
     bool hstr_active;
     /* True if memory operations require alignment */
     bool align_mem;
+    /* True if PSTATE.IL is set */
+    bool pstate_il;
     /*
      * >= 0, a copy of PSTATE.BTYPE, which will be 0 without v8.5-BTI.
      *  < 0, set by the current instruction.
diff --git a/target/arm/helper-a64.c b/target/arm/helper-a64.c
index 26f79f9141..19445b3c94 100644
--- a/target/arm/helper-a64.c
+++ b/target/arm/helper-a64.c
@@ -1071,6 +1071,7 @@ illegal_return:
     if (!arm_singlestep_active(env)) {
         env->pstate &= ~PSTATE_SS;
     }
+    helper_rebuild_hflags_a64(env, cur_el);
     qemu_log_mask(LOG_GUEST_ERROR, "Illegal exception return at EL%d: "
                   "resuming execution at 0x%" PRIx64 "\n", cur_el, env->pc);
 }
diff --git a/target/arm/helper.c b/target/arm/helper.c
index 155d8bf239..201ecf8c67 100644
--- a/target/arm/helper.c
+++ b/target/arm/helper.c
@@ -13408,6 +13408,10 @@ static CPUARMTBFlags rebuild_hflags_a32(CPUARMState *env, int fp_el,
         DP_TBFLAG_A32(flags, HSTR_ACTIVE, 1);
     }
 
+    if (env->uncached_cpsr & CPSR_IL) {
+        DP_TBFLAG_ANY(flags, PSTATE__IL, 1);
+    }
+
     return rebuild_hflags_common_32(env, fp_el, mmu_idx, flags);
 }
 
@@ -13502,6 +13506,10 @@ static CPUARMTBFlags rebuild_hflags_a64(CPUARMState *env, int el, int fp_el,
         }
     }
 
+    if (env->pstate & PSTATE_IL) {
+        DP_TBFLAG_ANY(flags, PSTATE__IL, 1);
+    }
+
     if (cpu_isar_feature(aa64_mte, env_archcpu(env))) {
         /*
          * Set MTE_ACTIVE if any access may be Checked, and leave clear
diff --git a/target/arm/translate-a64.c b/target/arm/translate-a64.c
index 422e2ac0c9..230cc8d83b 100644
--- a/target/arm/translate-a64.c
+++ b/target/arm/translate-a64.c
@@ -14662,6 +14662,16 @@ static void disas_a64_insn(CPUARMState *env, DisasContext *s)
     s->fp_access_checked = false;
     s->sve_access_checked = false;
 
+    if (s->pstate_il) {
+        /*
+         * Illegal execution state. This has priority over BTI
+         * exceptions, but comes after instruction abort exceptions.
+         */
+        gen_exception_insn(s, s->pc_curr, EXCP_UDEF,
+                           syn_illegalstate(), default_exception_el(s));
+        return;
+    }
+
     if (dc_isar_feature(aa64_bti, s)) {
         if (s->base.num_insns == 1) {
             /*
@@ -14780,6 +14790,7 @@ static void aarch64_tr_init_disas_context(DisasContextBase *dcbase,
 #endif
     dc->fp_excp_el = EX_TBFLAG_ANY(tb_flags, FPEXC_EL);
     dc->align_mem = EX_TBFLAG_ANY(tb_flags, ALIGN_MEM);
+    dc->pstate_il = EX_TBFLAG_ANY(tb_flags, PSTATE__IL);
     dc->sve_excp_el = EX_TBFLAG_A64(tb_flags, SVEEXC_EL);
     dc->sve_len = (EX_TBFLAG_A64(tb_flags, ZCR_LEN) + 1) * 16;
     dc->pauth_active = EX_TBFLAG_A64(tb_flags, PAUTH_ACTIVE);
diff --git a/target/arm/translate.c b/target/arm/translate.c
index 80c282669f..5e0fc8a0a0 100644
--- a/target/arm/translate.c
+++ b/target/arm/translate.c
@@ -9045,6 +9045,16 @@ static void disas_arm_insn(DisasContext *s, unsigned int insn)
         return;
     }
 
+    if (s->pstate_il) {
+        /*
+         * Illegal execution state. This has priority over BTI
+         * exceptions, but comes after instruction abort exceptions.
+         */
+        gen_exception_insn(s, s->pc_curr, EXCP_UDEF,
+                           syn_illegalstate(), default_exception_el(s));
+        return;
+    }
+
     if (cond == 0xf) {
         /* In ARMv3 and v4 the NV condition is UNPREDICTABLE; we
          * choose to UNDEF. In ARMv5 and above the space is used
@@ -9313,6 +9323,7 @@ static void arm_tr_init_disas_context(DisasContextBase *dcbase, CPUState *cs)
 #endif
     dc->fp_excp_el = EX_TBFLAG_ANY(tb_flags, FPEXC_EL);
     dc->align_mem = EX_TBFLAG_ANY(tb_flags, ALIGN_MEM);
+    dc->pstate_il = EX_TBFLAG_ANY(tb_flags, PSTATE__IL);
 
     if (arm_feature(env, ARM_FEATURE_M)) {
         dc->vfp_enabled = 1;
@@ -9576,6 +9587,16 @@ static void thumb_tr_translate_insn(DisasContextBase *dcbase, CPUState *cpu)
     }
     dc->insn = insn;
 
+    if (dc->pstate_il) {
+        /*
+         * Illegal execution state. This has priority over BTI
+         * exceptions, but comes after instruction abort exceptions.
+         */
+        gen_exception_insn(dc, dc->pc_curr, EXCP_UDEF,
+                           syn_illegalstate(), default_exception_el(dc));
+        return;
+    }
+
     if (dc->eci) {
         /*
          * For M-profile continuable instructions, ECI/ICI handling
-- 
2.25.1