Make linux_ptrace_attach_fail_reason return an std::string

This patch makes linux_ptrace_attach_fail_reason and
linux_ptrace_attach_fail_reason_string return std::string.  It also
replaces usages of struct buffer with std::string.  This allows getting
rid of a cleanup in in linux_ptrace_attach_fail_reason_string and
simplifies the code in general.

Something that looks odd to me is that in
linux_ptrace_attach_fail_reason, if the two messages are appended, there
is no separating space or \n, so the result won't be very nice.  I left
it as-is for now though.

gdb/ChangeLog:

	* nat/linux-ptrace.h (linux_ptrace_attach_fail_reason): Return
	std::string.
	(linux_ptrace_attach_fail_reason_string): Likewise.
	* nat/linux-ptrace.c (linux_ptrace_attach_fail_reason):
	Likewise.
	(linux_ptrace_attach_fail_reason_string): Likewise.
	* linux-nat.c (attach_proc_task_lwp_callback): Adjust.

gdb/gdbserver/ChangeLog:

	* linux-low.c (attach_proc_task_lwp_callback): Adjust to
	linux_ptrace_attach_fail_reason_string now returning an
	std::string.
	(linux_attach): Likewise.
	* thread-db.c (attach_thread): Likewise.

2 files changed, 26 insertions, 37 deletions

diff --git a/gdb/nat/linux-ptrace.c b/gdb/nat/linux-ptrace.c
index ac6ba72..5c4ddc9 100644
--- a/gdb/nat/linux-ptrace.c
+++ b/gdb/nat/linux-ptrace.c
@@ -32,51 +32,42 @@
    of 0 means there are no supported features.  */
 static int supported_ptrace_options = -1;
 
-/* Find all possible reasons we could fail to attach PID and append
-   these as strings to the already initialized BUFFER.  '\0'
-   termination of BUFFER must be done by the caller.  */
+/* Find all possible reasons we could fail to attach PID and return these
+   as a string.  An empty string is returned if we didn't find any reason.  */
 
-void
-linux_ptrace_attach_fail_reason (pid_t pid, struct buffer *buffer)
+std::string
+linux_ptrace_attach_fail_reason (pid_t pid)
 {
-  pid_t tracerpid;
+  pid_t tracerpid = linux_proc_get_tracerpid_nowarn (pid);
+  std::string result;
 
-  tracerpid = linux_proc_get_tracerpid_nowarn (pid);
   if (tracerpid > 0)
-    buffer_xml_printf (buffer, _("process %d is already traced "
-				 "by process %d"),
-		       (int) pid, (int) tracerpid);
+    string_appendf (result,
+		    _("process %d is already traced by process %d"),
+		    (int) pid, (int) tracerpid);
 
   if (linux_proc_pid_is_zombie_nowarn (pid))
-    buffer_xml_printf (buffer, _("process %d is a zombie "
-				 "- the process has already terminated"),
-		       (int) pid);
+    string_appendf (result,
+		    _("process %d is a zombie - the process has already "
+		      "terminated"),
+		    (int) pid);
+
+  return result;
 }
 
 /* See linux-ptrace.h.  */
 
-char *
+std::string
 linux_ptrace_attach_fail_reason_string (ptid_t ptid, int err)
 {
-  static char *reason_string;
-  struct buffer buffer;
-  char *warnings;
-  long lwpid = ptid_get_lwp (ptid);
-
-  xfree (reason_string);
-
-  buffer_init (&buffer);
-  linux_ptrace_attach_fail_reason (lwpid, &buffer);
-  buffer_grow_str0 (&buffer, "");
-  warnings = buffer_finish (&buffer);
-  if (warnings[0] != '\0')
-    reason_string = xstrprintf ("%s (%d), %s",
-				safe_strerror (err), err, warnings);
+  long lwpid = ptid.lwp ();
+  std::string reason = linux_ptrace_attach_fail_reason (lwpid);
+
+  if (!reason.empty ())
+    return string_printf ("%s (%d), %s", safe_strerror (err), err,
+			  reason.c_str ());
   else
-    reason_string = xstrprintf ("%s (%d)",
-				safe_strerror (err), err);
-  xfree (warnings);
-  return reason_string;
+    return string_printf ("%s (%d)", safe_strerror (err), err);
 }
 
 #if defined __i386__ || defined __x86_64__
diff --git a/gdb/nat/linux-ptrace.h b/gdb/nat/linux-ptrace.h
index 1f960ed..60967a3 100644
--- a/gdb/nat/linux-ptrace.h
+++ b/gdb/nat/linux-ptrace.h
@@ -180,14 +180,12 @@ struct buffer;
 # define TRAP_HWBKPT 4
 #endif
 
-extern void linux_ptrace_attach_fail_reason (pid_t pid, struct buffer *buffer);
+extern std::string linux_ptrace_attach_fail_reason (pid_t pid);
 
 /* Find all possible reasons we could have failed to attach to PTID
    and return them as a string.  ERR is the error PTRACE_ATTACH failed
-   with (an errno).  The result is stored in a static buffer.  This
-   string should be copied into a buffer by the client if the string
-   will not be immediately used, or if it must persist.  */
-extern char *linux_ptrace_attach_fail_reason_string (ptid_t ptid, int err);
+   with (an errno).  */
+extern std::string linux_ptrace_attach_fail_reason_string (ptid_t ptid, int err);
 
 extern void linux_ptrace_init_warnings (void);
 extern void linux_check_ptrace_features (void);