[PATCH v2] target/arm/cpu64: Use 32-bit GDBstub when running in 32-bit KVM mode

[Ard Biesheuvel <ardb@kernel.org>]

When running under KVM, we may decide to run the CPU in 32-bit mode, by
setting the 'aarch64=off' CPU option. In this case, we need to switch to
the 32-bit version of the GDB stub too, so that GDB has the correct view
of the CPU state. Without this, GDB debugging does not work at all, and
errors out upon connecting to the target with a mysterious 'g' packet
length error.

Cc: Richard Henderson <richard.henderson@linaro.org>
Cc: Peter Maydell <peter.maydell@linaro.org>
Cc: Alex Bennee <alex.bennee@linaro.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
v2: refactor existing CPUClass::gdb_... member assignments for the
    32-bit code so we can reuse it for the 64-bit code

 target/arm/cpu.c   | 16 +++++++++++-----
 target/arm/cpu.h   |  2 ++
 target/arm/cpu64.c |  3 +++
 3 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/target/arm/cpu.c b/target/arm/cpu.c
index a211804fd3df..ae8e78fc1472 100644
--- a/target/arm/cpu.c
+++ b/target/arm/cpu.c
@@ -2049,6 +2049,15 @@ static const struct TCGCPUOps arm_tcg_ops = {
 };
 #endif /* CONFIG_TCG */
 
+void arm_cpu_class_gdb_init(CPUClass *cc)
+{
+    cc->gdb_read_register = arm_cpu_gdb_read_register;
+    cc->gdb_write_register = arm_cpu_gdb_write_register;
+    cc->gdb_num_core_regs = 26;
+    cc->gdb_core_xml_file = "arm-core.xml";
+    cc->gdb_arch_name = arm_gdb_arch_name;
+}
+
 static void arm_cpu_class_init(ObjectClass *oc, void *data)
 {
     ARMCPUClass *acc = ARM_CPU_CLASS(oc);
@@ -2061,18 +2070,15 @@ static void arm_cpu_class_init(ObjectClass *oc, void *data)
     device_class_set_props(dc, arm_cpu_properties);
     device_class_set_parent_reset(dc, arm_cpu_reset, &acc->parent_reset);
 
+    arm_cpu_class_gdb_init(cc);
+
     cc->class_by_name = arm_cpu_class_by_name;
     cc->has_work = arm_cpu_has_work;
     cc->dump_state = arm_cpu_dump_state;
     cc->set_pc = arm_cpu_set_pc;
-    cc->gdb_read_register = arm_cpu_gdb_read_register;
-    cc->gdb_write_register = arm_cpu_gdb_write_register;
 #ifndef CONFIG_USER_ONLY
     cc->sysemu_ops = &arm_sysemu_ops;
 #endif
-    cc->gdb_num_core_regs = 26;
-    cc->gdb_core_xml_file = "arm-core.xml";
-    cc->gdb_arch_name = arm_gdb_arch_name;
     cc->gdb_get_dynamic_xml = arm_gdb_get_dynamic_xml;
     cc->gdb_stop_before_watchpoint = true;
     cc->disas_set_info = arm_disas_set_info;
diff --git a/target/arm/cpu.h b/target/arm/cpu.h
index e33f37b70ada..208da8e35697 100644
--- a/target/arm/cpu.h
+++ b/target/arm/cpu.h
@@ -1064,6 +1064,8 @@ int arm_gen_dynamic_svereg_xml(CPUState *cpu, int base_reg);
  */
 const char *arm_gdb_get_dynamic_xml(CPUState *cpu, const char *xmlname);
 
+void arm_cpu_class_gdb_init(CPUClass *cc);
+
 int arm_cpu_write_elf64_note(WriteCoreDumpFunction f, CPUState *cs,
                              int cpuid, void *opaque);
 int arm_cpu_write_elf32_note(WriteCoreDumpFunction f, CPUState *cs,
diff --git a/target/arm/cpu64.c b/target/arm/cpu64.c
index 15245a60a8c7..df7667864e11 100644
--- a/target/arm/cpu64.c
+++ b/target/arm/cpu64.c
@@ -906,6 +906,7 @@ static bool aarch64_cpu_get_aarch64(Object *obj, Error **errp)
 static void aarch64_cpu_set_aarch64(Object *obj, bool value, Error **errp)
 {
     ARMCPU *cpu = ARM_CPU(obj);
+    CPUClass *cc = CPU_GET_CLASS(obj);
 
     /* At this time, this property is only allowed if KVM is enabled.  This
      * restriction allows us to avoid fixing up functionality that assumes a
@@ -919,6 +920,8 @@ static void aarch64_cpu_set_aarch64(Object *obj, bool value, Error **errp)
             return;
         }
         unset_feature(&cpu->env, ARM_FEATURE_AARCH64);
+
+        arm_cpu_class_gdb_init(cc)
     } else {
         set_feature(&cpu->env, ARM_FEATURE_AARCH64);
     }
-- 
2.30.2