target/arm: Advertise MVE to gdb when present

Cortex-M CPUs with MVE should advertise this fact to gdb, using the
org.gnu.gdb.arm.m-profile-mve XML feature, which defines the VPR
register.  Presence of this feature also tells gdb to create
pseudo-registers Q0..Q7, so we do not need to tell gdb about them
separately.

Note that unless you have a very recent GDB that includes this fix:
http://patches-tcwg.linaro.org/patch/58133/ gdb will mis-print the
individual fields of the VPR register as zero (but showing the whole
thing as hex, eg with "print /x $vpr" will give the correct value).

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20211101160814.5103-1-peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

1 files changed, 25 insertions, 0 deletions

diff --git a/target/arm/gdbstub.c b/target/arm/gdbstub.c
index e0dcb33e32..134da0d0ae 100644
--- a/target/arm/gdbstub.c
+++ b/target/arm/gdbstub.c
@@ -199,6 +199,27 @@ static int vfp_gdb_set_sysreg(CPUARMState *env, uint8_t *buf, int reg)
     return 0;
 }
 
+static int mve_gdb_get_reg(CPUARMState *env, GByteArray *buf, int reg)
+{
+    switch (reg) {
+    case 0:
+        return gdb_get_reg32(buf, env->v7m.vpr);
+    default:
+        return 0;
+    }
+}
+
+static int mve_gdb_set_reg(CPUARMState *env, uint8_t *buf, int reg)
+{
+    switch (reg) {
+    case 0:
+        env->v7m.vpr = ldl_p(buf);
+        return 4;
+    default:
+        return 0;
+    }
+}
+
 /**
  * arm_get/set_gdb_*: get/set a gdb register
  * @env: the CPU state
@@ -468,6 +489,10 @@ void arm_cpu_register_gdb_regs_for_features(ARMCPU *cpu)
                                      2, "arm-vfp-sysregs.xml", 0);
         }
     }
+    if (cpu_isar_feature(aa32_mve, cpu)) {
+        gdb_register_coprocessor(cs, mve_gdb_get_reg, mve_gdb_set_reg,
+                                 1, "arm-m-profile-mve.xml", 0);
+    }
     gdb_register_coprocessor(cs, arm_gdb_get_sysreg, arm_gdb_set_sysreg,
                              arm_gen_dynamic_sysreg_xml(cs, cs->gdb_num_regs),
                              "system-registers.xml", 0);