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.

3 files changed, 21 insertions, 7 deletions

diff --git a/gdb/gdbserver/ChangeLog b/gdb/gdbserver/ChangeLog
index d91e004..f183655 100644
--- a/gdb/gdbserver/ChangeLog
+++ b/gdb/gdbserver/ChangeLog
@@ -1,3 +1,11 @@
+2018-01-17  Simon Marchi  <simon.marchi@ericsson.com>
+
+	* 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.
+
 2018-01-17  Eldar Abusalimov  <eldar.abusalimov@jetbrains.com>
 
 	PR gdb/21559
diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c
index d8e1226..8117fc6 100644
--- a/gdb/gdbserver/linux-low.c
+++ b/gdb/gdbserver/linux-low.c
@@ -1159,9 +1159,10 @@ attach_proc_task_lwp_callback (ptid_t ptid)
 	}
       else if (err != 0)
 	{
-	  warning (_("Cannot attach to lwp %d: %s"),
-		   lwpid,
-		   linux_ptrace_attach_fail_reason_string (ptid, err));
+	  std::string reason
+	    = linux_ptrace_attach_fail_reason_string (ptid, err);
+
+	  warning (_("Cannot attach to lwp %d: %s"), lwpid, reason.c_str ());
 	}
 
       return 1;
@@ -1186,8 +1187,11 @@ linux_attach (unsigned long pid)
      soon.  */
   err = linux_attach_lwp (ptid);
   if (err != 0)
-    error ("Cannot attach to process %ld: %s",
-	   pid, linux_ptrace_attach_fail_reason_string (ptid, err));
+    {
+      std::string reason = linux_ptrace_attach_fail_reason_string (ptid, err);
+
+      error ("Cannot attach to process %ld: %s", pid, reason.c_str ());
+    }
 
   proc = linux_add_process (pid, 1);
 
diff --git a/gdb/gdbserver/thread-db.c b/gdb/gdbserver/thread-db.c
index 6829fcc..812aa0f 100644
--- a/gdb/gdbserver/thread-db.c
+++ b/gdb/gdbserver/thread-db.c
@@ -225,9 +225,11 @@ attach_thread (const td_thrhandle_t *th_p, td_thrinfo_t *ti_p)
   err = linux_attach_lwp (ptid);
   if (err != 0)
     {
+      std::string reason = linux_ptrace_attach_fail_reason_string (ptid, err);
+
       warning ("Could not attach to thread %ld (LWP %d): %s\n",
-	       (unsigned long) ti_p->ti_tid, ti_p->ti_lid,
-	       linux_ptrace_attach_fail_reason_string (ptid, err));
+	       (unsigned long) ti_p->ti_tid, ti_p->ti_lid, reason.c_str ());
+
       return 0;
     }