[PATCH 06/10] target/m68k: expose system registers via GDB

["Marc-André Lureau" <marcandre.lureau@redhat.com>]

Add an m68k-system.xml GDB feature that exposes supervisor stack
pointers (ssp, usp, isp), function code registers (sfc, dfc), MMU
registers (urp, srp, dttr0/1, ittr0/1, mmusr) as read-only system
registers through the GDB coprocessor interface.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
---
 configs/targets/m68k-softmmu.mak |  2 +-
 gdbstub/gdb-xml/m68k-system.xml  | 32 +++++++++++++++++++++++++++
 target/m68k/helper.c             | 47 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 80 insertions(+), 1 deletion(-)

diff --git a/configs/targets/m68k-softmmu.mak b/configs/targets/m68k-softmmu.mak
index 0bc889f326e3..f3ac9b74c862 100644
--- a/configs/targets/m68k-softmmu.mak
+++ b/configs/targets/m68k-softmmu.mak
@@ -1,4 +1,4 @@
 TARGET_ARCH=m68k
 TARGET_BIG_ENDIAN=y
-TARGET_XML_FILES= cf-core.xml cf-fp.xml m68k-core.xml m68k-fp.xml
+TARGET_XML_FILES= cf-core.xml cf-fp.xml m68k-core.xml m68k-fp.xml m68k-system.xml
 TARGET_LONG_BITS=32
diff --git a/gdbstub/gdb-xml/m68k-system.xml b/gdbstub/gdb-xml/m68k-system.xml
new file mode 100644
index 000000000000..0a91be0edc00
--- /dev/null
+++ b/gdbstub/gdb-xml/m68k-system.xml
@@ -0,0 +1,32 @@
+<?xml version="1.0"?>
+<!--
+  SPDX-License-Identifier: GPL-2.0-or-later
+-->
+<!DOCTYPE feature SYSTEM "gdb-target.dtd">
+<!-- System-register values are read-only; writes are ignored. -->
+<feature name="org.qemu.gdb.m68k.system">
+  <reg name="ssp" bitsize="32" type="uint32"
+       group="qemu-debug" save-restore="no"/>
+  <reg name="usp" bitsize="32" type="uint32"
+       group="qemu-debug" save-restore="no"/>
+  <reg name="isp" bitsize="32" type="uint32"
+       group="qemu-debug" save-restore="no"/>
+  <reg name="sfc" bitsize="32" type="uint32"
+       group="qemu-debug" save-restore="no"/>
+  <reg name="dfc" bitsize="32" type="uint32"
+       group="qemu-debug" save-restore="no"/>
+  <reg name="urp" bitsize="32" type="uint32"
+       group="qemu-debug" save-restore="no"/>
+  <reg name="srp" bitsize="32" type="uint32"
+       group="qemu-debug" save-restore="no"/>
+  <reg name="dttr0" bitsize="32" type="uint32"
+       group="qemu-debug" save-restore="no"/>
+  <reg name="dttr1" bitsize="32" type="uint32"
+       group="qemu-debug" save-restore="no"/>
+  <reg name="ittr0" bitsize="32" type="uint32"
+       group="qemu-debug" save-restore="no"/>
+  <reg name="ittr1" bitsize="32" type="uint32"
+       group="qemu-debug" save-restore="no"/>
+  <reg name="mmusr" bitsize="32" type="uint32"
+       group="qemu-debug" save-restore="no"/>
+</feature>
diff --git a/target/m68k/helper.c b/target/m68k/helper.c
index 5f91d206f596..f2615d5bcfb8 100644
--- a/target/m68k/helper.c
+++ b/target/m68k/helper.c
@@ -123,6 +123,48 @@ static int m68k_fpu_gdb_set_reg(CPUState *cs, uint8_t *mem_buf, int n)
     return 0;
 }
 
+#ifndef CONFIG_USER_ONLY
+static int m68k_gdb_read_system_register(CPUState *cs, GByteArray *buf, int n)
+{
+    CPUM68KState *env = cpu_env(cs);
+    static const int stacks[] = { M68K_SSP, M68K_USP, M68K_ISP };
+
+    if (n >= 0 && n < ARRAY_SIZE(stacks)) {
+        int sp = stacks[n];
+
+        return gdb_get_reg32(buf, env->sp[sp]);
+    }
+    switch (n) {
+    case 3:
+        return gdb_get_reg32(buf, env->sfc);
+    case 4:
+        return gdb_get_reg32(buf, env->dfc);
+    case 5:
+        return gdb_get_reg32(buf, env->mmu.urp);
+    case 6:
+        return gdb_get_reg32(buf, env->mmu.srp);
+    case 7:
+        return gdb_get_reg32(buf, env->mmu.ttr[M68K_DTTR0]);
+    case 8:
+        return gdb_get_reg32(buf, env->mmu.ttr[M68K_DTTR1]);
+    case 9:
+        return gdb_get_reg32(buf, env->mmu.ttr[M68K_ITTR0]);
+    case 10:
+        return gdb_get_reg32(buf, env->mmu.ttr[M68K_ITTR1]);
+    case 11:
+        return gdb_get_reg32(buf, env->mmu.mmusr);
+    default:
+        return 0;
+    }
+}
+
+static int m68k_gdb_write_system_register(CPUState *cs, uint8_t *buf, int n)
+{
+    /* These registers are exposed for inspection only. Ignore writes. */
+    return 4;
+}
+#endif
+
 void m68k_cpu_init_gdb(M68kCPU *cpu)
 {
     CPUState *cs = CPU(cpu);
@@ -135,6 +177,11 @@ void m68k_cpu_init_gdb(M68kCPU *cpu)
         gdb_register_coprocessor(cs, m68k_fpu_gdb_get_reg, m68k_fpu_gdb_set_reg,
                                  gdb_find_static_feature("m68k-fp.xml"));
     }
+#ifndef CONFIG_USER_ONLY
+    gdb_register_coprocessor(cs, m68k_gdb_read_system_register,
+                             m68k_gdb_write_system_register,
+                             gdb_find_static_feature("m68k-system.xml"));
+#endif
     /* TODO: Add [E]MAC registers.  */
 }
 

-- 
2.55.0.543.g5ebe2ebe4ea8