Make stap-probe.c:stap_parse_register_operand's "regname" an std::string

This patch simplifies the code of
stap-probe.c:stap_parse_register_operand by making "regname" an
std::string.  No functionality change.

I'm this code's maintainer, so I'm pushing this as it's a fairly
trivial patch.

gdb/ChangeLog:
2019-05-16  Sergio Durigan Junior  <sergiodj@redhat.com>

	* stap-probe.c (stap_parse_register_operand): Make "regname" an
	"std::string", simplifying the algorithm.

2 files changed, 17 insertions, 24 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index faee999..2dc9198 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,10 @@
 2019-05-16  Sergio Durigan Junior  <sergiodj@redhat.com>
 
+	* stap-probe.c (stap_parse_register_operand): Make "regname" an
+	"std::string", simplifying the algorithm.
+
+2019-05-16  Sergio Durigan Junior  <sergiodj@redhat.com>
+
 	* stap-probe.c (handle_stap_probe): Fix complaint formatting.
 	(stap_static_probe_ops::get_probes): Likewise.
 
diff --git a/gdb/stap-probe.c b/gdb/stap-probe.c
index 5261a1a..e5a901b 100644
--- a/gdb/stap-probe.c
+++ b/gdb/stap-probe.c
@@ -687,12 +687,8 @@ stap_parse_register_operand (struct stap_parse_info *p)
   /* Variables used to extract the register name from the probe's
      argument.  */
   const char *start;
-  char *regname;
-  int len;
   const char *gdb_reg_prefix = gdbarch_stap_gdb_register_prefix (gdbarch);
-  int gdb_reg_prefix_len = gdb_reg_prefix ? strlen (gdb_reg_prefix) : 0;
   const char *gdb_reg_suffix = gdbarch_stap_gdb_register_suffix (gdbarch);
-  int gdb_reg_suffix_len = gdb_reg_suffix ? strlen (gdb_reg_suffix) : 0;
   const char *reg_prefix;
   const char *reg_ind_prefix;
   const char *reg_suffix;
@@ -753,37 +749,29 @@ stap_parse_register_operand (struct stap_parse_info *p)
   while (isalnum (*p->arg))
     ++p->arg;
 
-  len = p->arg - start;
-
-  regname = (char *) alloca (len + gdb_reg_prefix_len + gdb_reg_suffix_len + 1);
-  regname[0] = '\0';
+  std::string regname (start, p->arg - start);
 
   /* We only add the GDB's register prefix/suffix if we are dealing with
      a numeric register.  */
-  if (gdb_reg_prefix && isdigit (*start))
+  if (isdigit (*start))
     {
-      strncpy (regname, gdb_reg_prefix, gdb_reg_prefix_len);
-      strncpy (regname + gdb_reg_prefix_len, start, len);
-
-      if (gdb_reg_suffix)
-	strncpy (regname + gdb_reg_prefix_len + len,
-		 gdb_reg_suffix, gdb_reg_suffix_len);
+      if (gdb_reg_prefix != NULL)
+	regname = gdb_reg_prefix + regname;
 
-      len += gdb_reg_prefix_len + gdb_reg_suffix_len;
+      if (gdb_reg_suffix != NULL)
+	regname += gdb_reg_suffix;
     }
-  else
-    strncpy (regname, start, len);
-
-  regname[len] = '\0';
 
   /* Is this a valid register name?  */
-  if (user_reg_map_name_to_regnum (gdbarch, regname, len) == -1)
+  if (user_reg_map_name_to_regnum (gdbarch,
+				   regname.c_str (),
+				   regname.size ()) == -1)
     error (_("Invalid register name `%s' on expression `%s'."),
-	   regname, p->saved_arg);
+	   regname.c_str (), p->saved_arg);
 
   write_exp_elt_opcode (&p->pstate, OP_REGISTER);
-  str.ptr = regname;
-  str.length = len;
+  str.ptr = regname.c_str ();
+  str.length = regname.size ();
   write_exp_string (&p->pstate, str);
   write_exp_elt_opcode (&p->pstate, OP_REGISTER);