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armv7m: Replace armv7m.hack with unassigned_access handler

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For v7m we need to catch attempts to execute from special
addresses at 0xfffffff0 and above. Previously we did this
with the aid of a hacky special purpose lump of memory
in the address space and a check in translate.c for whether
we were translating code at those addresses.

We can implement this more cleanly using a CPU
unassigned access handler which throws the exception
if the unassigned access is for one of the special addresses.

Signed-off-by: Michael Davidsaver <mdavidsaver@gmail.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-id: 1484937883-1068-3-git-send-email-peter.maydell@linaro.org
[PMM:
 * drop the deletion of the "don't interrupt if PC is magic"
   code in arm_v7m_cpu_exec_interrupt() -- this is still
   required
 * don't generate an exception for unassigned accesses
   which aren't to the magic address -- although doing
   this is in theory correct in practice it will break
   currently working guests which rely on the RAZ/WI
   behaviour when they touch devices which we haven't
   modelled.
 * trigger EXCP_EXCEPTION_EXIT on is_exec, not !is_write
]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
This commit is contained in:
Michael Davidsaver 2017-01-27 15:20:21 +00:00 committed by Peter Maydell
parent 58117c9bb4
commit 542b3478a0
3 changed files with 34 additions and 14 deletions
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8
hw/arm/armv7m.c
View file

@ -180,7 +180,6 @@ 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";
@ -225,13 +224,6 @@ 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;
}

28
target/arm/cpu.c
View file

@ -292,6 +292,33 @@ 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);
@ -1016,6 +1043,7 @@ 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;
}

12
target/arm/translate.c
View file

@ -11719,12 +11719,12 @@ void gen_intermediate_code(CPUARMState *env, TranslationBlock *tb)
break;
}
#else
if (dc->pc >= 0xfffffff0 && arm_dc_feature(dc, ARM_FEATURE_M)) {
/* We always get here via a jump, so know we are not in a
conditional execution block. */
gen_exception_internal(EXCP_EXCEPTION_EXIT);
dc->is_jmp = DISAS_EXC;
break;
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