[Qemu-devel] [PULL 24/24] arm: Remove workarounds for old M-profile exception return implementation

[Peter Maydell]

Now that we've rewritten M-profile exception return so that the magic
PC values are not visible to other parts of QEMU, we can delete the
special casing of them elsewhere.

Signed-off-by: Peter Maydell <address@hidden>
Reviewed-by: Philippe Mathieu-Daudé <address@hidden>
Reviewed-by: Richard Henderson <address@hidden>
Message-id: address@hidden
---
 target/arm/cpu.c       | 43 ++-----------------------------------------
 target/arm/translate.c |  8 --------
 2 files changed, 2 insertions(+), 49 deletions(-)

diff --git a/target/arm/cpu.c b/target/arm/cpu.c
index 04b062c..b357aee 100644
--- a/target/arm/cpu.c
+++ b/target/arm/cpu.c
@@ -304,33 +304,6 @@ bool arm_cpu_exec_interrupt(CPUState *cs, int 
interrupt_request)
 }
 
 #if !defined(CONFIG_USER_ONLY) || !defined(TARGET_AARCH64)
-static void arm_v7m_unassigned_access(CPUState *cpu, hwaddr addr,
-                                      bool is_write, bool is_exec, int opaque,
-                                      unsigned size)
-{
-    ARMCPU *arm = ARM_CPU(cpu);
-    CPUARMState *env = &arm->env;
-
-    /* ARMv7-M interrupt return works by loading a magic value into the PC.
-     * On real hardware the load causes the return to occur.  The qemu
-     * implementation performs the jump normally, then does the exception
-     * return by throwing a special exception when when the CPU tries to
-     * execute code at the magic address.
-     */
-    if (env->v7m.exception != 0 && addr >= 0xfffffff0 && is_exec) {
-        cpu->exception_index = EXCP_EXCEPTION_EXIT;
-        cpu_loop_exit(cpu);
-    }
-
-    /* In real hardware an attempt to access parts of the address space
-     * with nothing there will usually cause an external abort.
-     * However our QEMU board models are often missing device models where
-     * the guest can boot anyway with the default read-as-zero/writes-ignored
-     * behaviour that you get without a QEMU unassigned_access hook.
-     * So just return here to retain that default behaviour.
-     */
-}
-
 static bool arm_v7m_cpu_exec_interrupt(CPUState *cs, int interrupt_request)
 {
     CPUClass *cc = CPU_GET_CLASS(cs);
@@ -338,17 +311,7 @@ static bool arm_v7m_cpu_exec_interrupt(CPUState *cs, int 
interrupt_request)
     CPUARMState *env = &cpu->env;
     bool ret = false;
 
-    /* ARMv7-M interrupt return works by loading a magic value
-     * into the PC.  On real hardware the load causes the
-     * return to occur.  The qemu implementation performs the
-     * jump normally, then does the exception return when the
-     * CPU tries to execute code at the magic address.
-     * This will cause the magic PC value to be pushed to
-     * the stack if an interrupt occurred at the wrong time.
-     * We avoid this by disabling interrupts when
-     * pc contains a magic address.
-     *
-     * ARMv7-M interrupt masking works differently than -A or -R.
+    /* ARMv7-M interrupt masking works differently than -A or -R.
      * There is no FIQ/IRQ distinction. Instead of I and F bits
      * masking FIQ and IRQ interrupts, an exception is taken only
      * if it is higher priority than the current execution priority
@@ -356,8 +319,7 @@ static bool arm_v7m_cpu_exec_interrupt(CPUState *cs, int 
interrupt_request)
      * currently active exception).
      */
     if (interrupt_request & CPU_INTERRUPT_HARD
-        && (armv7m_nvic_can_take_pending_exception(env->nvic))
-        && (env->regs[15] < 0xfffffff0)) {
+        && (armv7m_nvic_can_take_pending_exception(env->nvic))) {
         cs->exception_index = EXCP_IRQ;
         cc->do_interrupt(cs);
         ret = true;
@@ -1091,7 +1053,6 @@ static void arm_v7m_class_init(ObjectClass *oc, void 
*data)
     cc->do_interrupt = arm_v7m_cpu_do_interrupt;
 #endif
 
-    cc->do_unassigned_access = arm_v7m_unassigned_access;
     cc->cpu_exec_interrupt = arm_v7m_cpu_exec_interrupt;
 }
 
diff --git a/target/arm/translate.c b/target/arm/translate.c
index da03e153..0b5a0bc 100644
--- a/target/arm/translate.c
+++ b/target/arm/translate.c
@@ -11927,14 +11927,6 @@ void gen_intermediate_code(CPUARMState *env, 
TranslationBlock *tb)
             dc->is_jmp = DISAS_EXC;
             break;
         }
-#else
-        if (arm_dc_feature(dc, ARM_FEATURE_M)) {
-            /* Branches to the magic exception-return addresses should
-             * already have been caught via the arm_v7m_unassigned_access hook,
-             * and never get here.
-             */
-            assert(dc->pc < 0xfffffff0);
-        }
 #endif
 
         if (unlikely(!QTAILQ_EMPTY(&cs->breakpoints))) {
-- 
2.7.4