[Qemu-devel] [PATCH v6] target-ppc: gdbstub allow byte swapping for reading/writing registers

[Thomas Falcon]

This patch allows registers to be properly read from and written to
when using the gdbstub to debug a ppc guest running in little
endian mode.  It accomplishes this goal by byte swapping the values of
any registers if the MSR:LE value is set.

Signed-off-by: Thomas Falcon <address@hidden>
---
Differences from v5:

ppc_cpu_gdb_swap_register uses built in byte swapping functions
---
 target-ppc/cpu-qom.h        |   3 +
 target-ppc/gdbstub.c        | 139 +++++++++++++++++++++++++++++++++++---------
 target-ppc/translate_init.c |   4 +-
 3 files changed, 115 insertions(+), 31 deletions(-)

diff --git a/target-ppc/cpu-qom.h b/target-ppc/cpu-qom.h
index 72b2232..b85133c 100644
--- a/target-ppc/cpu-qom.h
+++ b/target-ppc/cpu-qom.h
@@ -107,9 +107,12 @@ void ppc_cpu_dump_state(CPUState *cpu, FILE *f, 
fprintf_function cpu_fprintf,
                         int flags);
 void ppc_cpu_dump_statistics(CPUState *cpu, FILE *f,
                              fprintf_function cpu_fprintf, int flags);
+void ppc_cpu_gdb_swap_register(uint8_t *buf, int reg);
 hwaddr ppc_cpu_get_phys_page_debug(CPUState *cpu, vaddr addr);
 int ppc_cpu_gdb_read_register(CPUState *cpu, uint8_t *buf, int reg);
+int ppc_cpu_gdb_read_register_wrap(CPUState *cpu, uint8_t *buf, int reg);
 int ppc_cpu_gdb_write_register(CPUState *cpu, uint8_t *buf, int reg);
+int ppc_cpu_gdb_write_register_wrap(CPUState *cpu, uint8_t *buf, int reg);
 int ppc64_cpu_write_elf64_qemunote(WriteCoreDumpFunction f,
                                    CPUState *cpu, void *opaque);
 int ppc64_cpu_write_elf64_note(WriteCoreDumpFunction f, CPUState *cs,
diff --git a/target-ppc/gdbstub.c b/target-ppc/gdbstub.c
index 1c91090..92649ed 100644
--- a/target-ppc/gdbstub.c
+++ b/target-ppc/gdbstub.c
@@ -21,6 +21,82 @@
 #include "qemu-common.h"
 #include "exec/gdbstub.h"
 
+static int ppc_cpu_gdb_register_len(int n)
+{
+    switch (n) {
+    case 0 ... 31:
+        /* gprs */
+        return sizeof(target_ulong);
+    case 32 ... 63:
+        /* fprs */
+        if (gdb_has_xml) {
+            return 0;
+        }
+        return 8;
+    case 66:
+        /* cr */
+        return 4;
+    case 64:
+        /* nip */
+    case 65:
+        /* msr */
+    case 67:
+        /* lr */
+    case 68:
+        /* ctr */
+    case 69:
+        /* xer */
+        return sizeof(target_ulong);
+    case 70:
+        /* fpscr */
+        if (gdb_has_xml) {
+            return 0;
+        }
+        return sizeof(target_ulong);
+    default:
+        return 0;
+    }
+}
+
+
+/* The following functions are used to ensure the correct
+ * transfer of registers between a little endian ppc target
+ * and a big endian host by checking the LE bit in the Machine State Register
+ */
+
+void ppc_cpu_gdb_swap_register(uint8_t *mem_buf, int n)
+{
+    int len = ppc_cpu_gdb_register_len(n);
+    if (len == 4) {
+        bswap32s((uint32_t *)mem_buf);
+    } else {
+        bswap64s((uint64_t *)mem_buf);
+    }
+}
+
+int ppc_cpu_gdb_read_register_wrap(CPUState *cs, uint8_t *mem_buf, int n)
+{
+    PowerPCCPU *cpu = POWERPC_CPU(cs);
+    CPUPPCState *env = &cpu->env;
+
+    int len = ppc_cpu_gdb_read_register(cs, mem_buf, n);
+    if (msr_le) {
+        ppc_cpu_gdb_swap_register(mem_buf, n);
+    }
+    return len;
+}
+
+int ppc_cpu_gdb_write_register_wrap(CPUState *cs, uint8_t *mem_buf, int n)
+{
+    PowerPCCPU *cpu = POWERPC_CPU(cs);
+    CPUPPCState *env = &cpu->env;
+
+    if (msr_le) {
+        ppc_cpu_gdb_swap_register(mem_buf, n);
+    }
+    return ppc_cpu_gdb_write_register(cs, mem_buf, n);
+}
+
 /* Old gdb always expects FP registers.  Newer (xml-aware) gdb only
  * expects whatever the target description contains.  Due to a
  * historical mishap the FP registers appear in between core integer
@@ -32,23 +108,26 @@ int ppc_cpu_gdb_read_register(CPUState *cs, uint8_t 
*mem_buf, int n)
 {
     PowerPCCPU *cpu = POWERPC_CPU(cs);
     CPUPPCState *env = &cpu->env;
+    int r = ppc_cpu_gdb_register_len(n);
+
+    if (!r) {
+        return r;
+    }
 
     if (n < 32) {
         /* gprs */
-        return gdb_get_regl(mem_buf, env->gpr[n]);
+        gdb_get_regl(mem_buf, env->gpr[n]);
     } else if (n < 64) {
         /* fprs */
-        if (gdb_has_xml) {
-            return 0;
-        }
         stfq_p(mem_buf, env->fpr[n-32]);
-        return 8;
     } else {
         switch (n) {
         case 64:
-            return gdb_get_regl(mem_buf, env->nip);
+            gdb_get_regl(mem_buf, env->nip);
+            break;
         case 65:
-            return gdb_get_regl(mem_buf, env->msr);
+            gdb_get_regl(mem_buf, env->msr);
+            break;
         case 66:
             {
                 uint32_t cr = 0;
@@ -56,50 +135,55 @@ int ppc_cpu_gdb_read_register(CPUState *cs, uint8_t 
*mem_buf, int n)
                 for (i = 0; i < 8; i++) {
                     cr |= env->crf[i] << (32 - ((i + 1) * 4));
                 }
-                return gdb_get_reg32(mem_buf, cr);
+                gdb_get_reg32(mem_buf, cr);
+                break;
             }
         case 67:
-            return gdb_get_regl(mem_buf, env->lr);
+            gdb_get_regl(mem_buf, env->lr);
+            break;
         case 68:
-            return gdb_get_regl(mem_buf, env->ctr);
+            gdb_get_regl(mem_buf, env->ctr);
+            break;
         case 69:
-            return gdb_get_regl(mem_buf, env->xer);
+            gdb_get_regl(mem_buf, env->xer);
+            break;
         case 70:
             {
                 if (gdb_has_xml) {
                     return 0;
                 }
-                return gdb_get_reg32(mem_buf, env->fpscr);
+                gdb_get_reg32(mem_buf, env->fpscr);
+                break;
             }
         }
     }
-    return 0;
+    return r;
 }
 
 int ppc_cpu_gdb_write_register(CPUState *cs, uint8_t *mem_buf, int n)
 {
     PowerPCCPU *cpu = POWERPC_CPU(cs);
     CPUPPCState *env = &cpu->env;
+    int r = ppc_cpu_gdb_register_len(n);
+
+    if (!r) {
+        return r;
+    }
 
     if (n < 32) {
         /* gprs */
         env->gpr[n] = ldtul_p(mem_buf);
-        return sizeof(target_ulong);
     } else if (n < 64) {
         /* fprs */
-        if (gdb_has_xml) {
-            return 0;
-        }
         env->fpr[n-32] = ldfq_p(mem_buf);
-        return 8;
     } else {
         switch (n) {
         case 64:
             env->nip = ldtul_p(mem_buf);
-            return sizeof(target_ulong);
+            break;
         case 65:
             ppc_store_msr(env, ldtul_p(mem_buf));
-            return sizeof(target_ulong);
+            break;
         case 66:
             {
                 uint32_t cr = ldl_p(mem_buf);
@@ -107,25 +191,22 @@ int ppc_cpu_gdb_write_register(CPUState *cs, uint8_t 
*mem_buf, int n)
                 for (i = 0; i < 8; i++) {
                     env->crf[i] = (cr >> (32 - ((i + 1) * 4))) & 0xF;
                 }
-                return 4;
+                break;
             }
         case 67:
             env->lr = ldtul_p(mem_buf);
-            return sizeof(target_ulong);
+            break;
         case 68:
             env->ctr = ldtul_p(mem_buf);
-            return sizeof(target_ulong);
+            break;
         case 69:
             env->xer = ldtul_p(mem_buf);
-            return sizeof(target_ulong);
+            break;
         case 70:
             /* fpscr */
-            if (gdb_has_xml) {
-                return 0;
-            }
             store_fpscr(env, ldtul_p(mem_buf), 0xffffffff);
-            return sizeof(target_ulong);
+            break;
         }
     }
-    return 0;
+    return r;
 }
diff --git a/target-ppc/translate_init.c b/target-ppc/translate_init.c
index 445c360..cf12ba7 100644
--- a/target-ppc/translate_init.c
+++ b/target-ppc/translate_init.c
@@ -8655,8 +8655,8 @@ static void ppc_cpu_class_init(ObjectClass *oc, void 
*data)
     cc->dump_state = ppc_cpu_dump_state;
     cc->dump_statistics = ppc_cpu_dump_statistics;
     cc->set_pc = ppc_cpu_set_pc;
-    cc->gdb_read_register = ppc_cpu_gdb_read_register;
-    cc->gdb_write_register = ppc_cpu_gdb_write_register;
+    cc->gdb_read_register = ppc_cpu_gdb_read_register_wrap;
+    cc->gdb_write_register = ppc_cpu_gdb_write_register_wrap;
 #ifndef CONFIG_USER_ONLY
     cc->get_phys_page_debug = ppc_cpu_get_phys_page_debug;
     cc->vmsd = &vmstate_ppc_cpu;
-- 
1.8.3.1