gdb/csky: remove nullptr return from csky_pseudo_register_name

Building on the previous commits, in this commit I remove two
instances of 'return NULL' from csky_pseudo_register_name, and replace
them with a return of the empty string.

These two are particularly interesting, and worth pulling into their
own commit, because these returns of NULL appear to be depended on
within other parts of the csky code.

In csky-linux-tdep.c in the register collect/supply code, GDB checks
for the register name being nullptr in order to decide if a target
supports a particular feature or not.  I've updated the code to check
for the empty string.

I have no way of testing this change.

2 files changed, 11 insertions, 20 deletions

diff --git a/gdb/csky-linux-tdep.c b/gdb/csky-linux-tdep.c
index 7bcc171..ea306cd 100644
--- a/gdb/csky-linux-tdep.c
+++ b/gdb/csky-linux-tdep.c
@@ -155,7 +155,7 @@ csky_supply_fregset (const struct regset *regset,
       /* Supply vr0~vr15.  */
       for (i = 0; i < 16; i ++)
 	{
-	  if (gdbarch_register_name (gdbarch, (CSKY_VR0_REGNUM + i)))
+	  if (*gdbarch_register_name (gdbarch, (CSKY_VR0_REGNUM + i)) != '\0')
 	    {
 	      offset = 16 * i;
 	      regcache->raw_supply (CSKY_VR0_REGNUM + i, fregs + offset);
@@ -164,7 +164,7 @@ csky_supply_fregset (const struct regset *regset,
       /* Supply fr0~fr15.  */
       for (i = 0; i < 16; i ++)
 	{
-	  if (gdbarch_register_name (gdbarch, (CSKY_FR0_REGNUM + i)))
+	  if (*gdbarch_register_name (gdbarch, (CSKY_FR0_REGNUM + i)) != '\0')
 	    {
 	      offset = 16 * i;
 	      regcache->raw_supply (CSKY_FR0_REGNUM + i, fregs + offset);
@@ -173,7 +173,7 @@ csky_supply_fregset (const struct regset *regset,
       /* Supply fr16~fr31.  */
       for (i = 0; i < 16; i ++)
 	{
-	  if (gdbarch_register_name (gdbarch, (CSKY_FR16_REGNUM + i)))
+	  if (*gdbarch_register_name (gdbarch, (CSKY_FR16_REGNUM + i)) != '\0')
 	    {
 	      offset = (16 * 16) + (8 * i);
 	      regcache->raw_supply (CSKY_FR16_REGNUM + i, fregs + offset);
@@ -182,7 +182,7 @@ csky_supply_fregset (const struct regset *regset,
      /* Supply fcr, fesr, fid.  */
       for (i = 0; i < 3; i ++)
 	{
-	  if (gdbarch_register_name (gdbarch, fcr_regno[i]))
+	  if (*gdbarch_register_name (gdbarch, fcr_regno[i]) != '\0')
 	    {
 	      offset = (16 * 16) + (16 * 8) + (4 * i);
 	      regcache->raw_supply (fcr_regno[i], fregs + offset);
@@ -245,7 +245,7 @@ csky_collect_fregset (const struct regset *regset,
       /* Supply vr0~vr15.  */
       for (i = 0; i < 16; i ++)
 	{
-	  if (gdbarch_register_name (gdbarch, (CSKY_VR0_REGNUM + i)))
+	  if (*gdbarch_register_name (gdbarch, (CSKY_VR0_REGNUM + i)) != '\0')
 	    {
 	      offset = 16 * i;
 	      regcache ->raw_collect (CSKY_VR0_REGNUM + i, fregs + offset);
@@ -254,7 +254,7 @@ csky_collect_fregset (const struct regset *regset,
       /* Supply fr16~fr31.  */
       for (i = 0; i < 16; i ++)
 	{
-	  if (gdbarch_register_name (gdbarch, (CSKY_FR16_REGNUM + i)))
+	  if (*gdbarch_register_name (gdbarch, (CSKY_FR16_REGNUM + i)) != '\0')
 	    {
 	      offset = (16 * 16) + (8 * i);
 	      regcache ->raw_collect (CSKY_FR16_REGNUM + i, fregs + offset);
@@ -263,7 +263,7 @@ csky_collect_fregset (const struct regset *regset,
       /* Supply fcr, fesr, fid.  */
       for (i = 0; i < 3; i ++)
 	{
-	  if (gdbarch_register_name (gdbarch, fcr_regno[i]))
+	  if (*gdbarch_register_name (gdbarch, fcr_regno[i]) != '\0')
 	    {
 	      offset = (16 * 16) + (16 * 8) + (4 * i);
 	      regcache ->raw_collect (fcr_regno[i], fregs + offset);
diff --git a/gdb/csky-tdep.c b/gdb/csky-tdep.c
index cbf12c1..17820aa 100644
--- a/gdb/csky-tdep.c
+++ b/gdb/csky-tdep.c
@@ -660,21 +660,12 @@ static const char * const csky_register_names[] =
 static const char *
 csky_register_name (struct gdbarch *gdbarch, int reg_nr)
 {
-  int num_regs = gdbarch_num_regs (gdbarch);
-  int num_pseudo_regs =  gdbarch_num_pseudo_regs (gdbarch);
-
-  if ((reg_nr >= num_regs) && (reg_nr < (num_regs + num_pseudo_regs)))
+  if (reg_nr >= gdbarch_num_regs (gdbarch))
     return csky_pseudo_register_name (gdbarch, reg_nr);
 
   if (tdesc_has_registers (gdbarch_target_desc (gdbarch)))
     return tdesc_register_name (gdbarch, reg_nr);
 
-  if (reg_nr < 0)
-    return NULL;
-
-  if (reg_nr >= gdbarch_num_regs (gdbarch))
-    return NULL;
-
   return csky_register_names[reg_nr];
 }
 
@@ -2543,15 +2534,15 @@ csky_pseudo_register_name (struct gdbarch *gdbarch, int regno)
       if (regno < tdep->fv_pseudo_registers_count)
         {
           if ((regno < 64) && ((regno % 4) >= 2) && !tdep->has_vr0)
-            return NULL;
+            return "";
           else if ((regno >= 64) && ((regno % 4) >= 2))
-            return NULL;
+            return "";
           else
             return fv_pseudo_names[regno];
         }
     }
 
-  return NULL;
+  return "";
 }
 
 /* Read for csky pseudo regs.  */