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.

1 files changed, 3 insertions, 5 deletions

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);