s390x/gdb: add gs registers

Let's provide the guarded storage registers via gdb server.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

configure

@@ -6231,7 +6231,7 @@ case "$target_name" in
     echo "TARGET_ABI32=y" >> $config_target_mak
   ;;
   s390x)
-    gdb_xml_files="s390x-core64.xml s390-acr.xml s390-fpr.xml s390-vx.xml s390-cr.xml s390-virt.xml"
+    gdb_xml_files="s390x-core64.xml s390-acr.xml s390-fpr.xml s390-vx.xml s390-cr.xml s390-virt.xml s390-gs.xml"
   ;;
   tilegx)
   ;;

gdb-xml/s390-gs.xml

@@ -0,0 +1,14 @@
+<?xml version="1.0"?>
+<!-- Copyright 2017 IBM Corp.
+
+     This work is licensed under the terms of the GNU GPL, version 2 or
+     (at your option) any later version. See the COPYING file in the
+     top-level directory. -->
+
+<!DOCTYPE feature SYSTEM "gdb-target.dtd">
+<feature name="org.gnu.gdb.s390.gs">
+  <reg name="gs_reserved" bitsize="64" type="uint64" group="system"/>
+  <reg name="gsd" bitsize="64" type="uint64" group="system"/>
+  <reg name="gssm" bitsize="64" type="uint64" group="system"/>
+  <reg name="gsepla" bitsize="64" type="data_ptr" group="system"/>
+</feature>

target/s390x/gdbstub.c

@@ -286,6 +286,26 @@ static int cpu_write_virt_reg(CPUS390XState *env, uint8_t *mem_buf, int n)
 }
 #endif
 
+/* the values represent the positions in s390-gs.xml */
+#define S390_GS_RESERVED_REGNUM 0
+#define S390_GS_GSD_REGNUM      1
+#define S390_GS_GSSM_REGNUM     2
+#define S390_GS_GSEPLA_REGNUM   3
+/* total number of registers in s390-gs.xml */
+#define S390_NUM_GS_REGS 4
+
+static int cpu_read_gs_reg(CPUS390XState *env, uint8_t *mem_buf, int n)
+{
+    return gdb_get_regl(mem_buf, env->gscb[n]);
+}
+
+static int cpu_write_gs_reg(CPUS390XState *env, uint8_t *mem_buf, int n)
+{
+    env->gscb[n] = ldtul_p(mem_buf);
+    cpu_synchronize_post_init(ENV_GET_CPU(env));
+    return 8;
+}
+
 void s390_cpu_gdb_init(CPUState *cs)
 {
     gdb_register_coprocessor(cs, cpu_read_ac_reg,
@@ -300,6 +320,10 @@ void s390_cpu_gdb_init(CPUState *cs)
                              cpu_write_vreg,
                              S390_NUM_VREGS, "s390-vx.xml", 0);
 
+    gdb_register_coprocessor(cs, cpu_read_gs_reg,
+                             cpu_write_gs_reg,
+                             S390_NUM_GS_REGS, "s390-gs.xml", 0);
+
 #ifndef CONFIG_USER_ONLY
     gdb_register_coprocessor(cs, cpu_read_c_reg,
                              cpu_write_c_reg,