[Qemu-devel] [PATCH v2 02/26] armv7m: Undo armv7m.hack

[Michael Davidsaver <mdavidsaver@gmail.com>]

Add CPU unassigned access handler in place of special
MemoryRegion to catch exception returns.

The unassigned handler will signal other faults as either
prefetch or data exceptions, with the FSR code 0x8 to
distinguish them from memory translation faults (0xd).
Future code will make use of this distinction when
deciding to raise BusFault or MemManage exceptions.
---
 hw/arm/armv7m.c  |  8 --------
 target-arm/cpu.c | 32 +++++++++++++++++++++-----------
 2 files changed, 21 insertions(+), 19 deletions(-)

diff --git a/hw/arm/armv7m.c b/hw/arm/armv7m.c
index a80d2ad..68146de 100644
--- a/hw/arm/armv7m.c
+++ b/hw/arm/armv7m.c
@@ -176,7 +176,6 @@ DeviceState *armv7m_init(MemoryRegion *system_memory, int mem_size, int num_irq,
     uint64_t entry;
     uint64_t lowaddr;
     int big_endian;
-    MemoryRegion *hack = g_new(MemoryRegion, 1);
 
     if (cpu_model == NULL) {
 	cpu_model = "cortex-m3";
@@ -221,13 +220,6 @@ DeviceState *armv7m_init(MemoryRegion *system_memory, int mem_size, int num_irq,
         }
     }
 
-    /* Hack to map an additional page of ram at the top of the address
-       space.  This stops qemu complaining about executing code outside RAM
-       when returning from an exception.  */
-    memory_region_init_ram(hack, NULL, "armv7m.hack", 0x1000, &error_fatal);
-    vmstate_register_ram_global(hack);
-    memory_region_add_subregion(system_memory, 0xfffff000, hack);
-
     qemu_register_reset(armv7m_reset, cpu);
     return nvic;
 }
diff --git a/target-arm/cpu.c b/target-arm/cpu.c
index 30739fc..728854f 100644
--- a/target-arm/cpu.c
+++ b/target-arm/cpu.c
@@ -280,6 +280,25 @@ 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;
+
+    env->exception.vaddress = addr;
+    env->exception.fsr = is_write ? 0x808 : 0x8; /* Precise External Abort */
+    if (env->v7m.exception != 0 && addr >= 0xfffffff0 && !is_write) {
+        cpu->exception_index = EXCP_EXCEPTION_EXIT;
+    } else if (is_exec) {
+        cpu->exception_index = EXCP_PREFETCH_ABORT;
+    } else {
+        cpu->exception_index = EXCP_DATA_ABORT;
+    }
+    cpu_loop_exit(cpu);
+}
+
 static bool arm_v7m_cpu_exec_interrupt(CPUState *cs, int interrupt_request)
 {
     CPUClass *cc = CPU_GET_CLASS(cs);
@@ -294,19 +313,9 @@ static bool arm_v7m_cpu_exec_interrupt(CPUState *cs, int interrupt_request)
         cc->do_interrupt(cs);
         ret = true;
     }
-    /* 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.
-     */
     if (interrupt_request & CPU_INTERRUPT_HARD
         && !(env->daif & PSTATE_I)
-        && (env->regs[15] < 0xfffffff0)) {
+            ) {
         cs->exception_index = EXCP_IRQ;
         cc->do_interrupt(cs);
         ret = true;
@@ -909,6 +918,7 @@ 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;
 }
 
-- 
2.1.4