libctf: lowest-level memory allocation and debug-dumping wrappers

The memory-allocation wrappers are simple things to allow malloc
interposition: they are only used inconsistently at present, usually
where malloc debugging was required in the past.

These provide a default implementation that is environment-variable
triggered (initialized on the first call to the libctf creation and
file-opening functions, the first functions people will use), and
a ctf_setdebug()/ctf_getdebug() pair that allows the caller to
explicitly turn debugging off and on.  If ctf_setdebug() is called,
the automatic setting from an environment variable is skipped.

libctf/
	* ctf-impl.h: New file.
	* ctf-subr.c: New file.

include/
	* ctf-api.h (ctf_setdebug): New.
	(ctf_getdebug): Likewise.

libctf/ctf-impl.h

@@ -0,0 +1,78 @@
+/* Implementation header.
+   Copyright (C) 2019 Free Software Foundation, Inc.
+
+   This file is part of libctf.
+
+   libctf is free software; you can redistribute it and/or modify it under
+   the terms of the GNU General Public License as published by the Free
+   Software Foundation; either version 3, or (at your option) any later
+   version.
+
+   This program is distributed in the hope that it will be useful, but
+   WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+   See the GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; see the file COPYING.  If not see
+   <http://www.gnu.org/licenses/>.  */
+
+#ifndef	_CTF_IMPL_H
+#define	_CTF_IMPL_H
+
+#include "config.h"
+#include <sys/errno.h>
+#include <ctf-api.h>
+#include <sys/types.h>
+
+#ifdef	__cplusplus
+extern "C"
+  {
+#endif
+
+/* Compiler attributes.  */
+
+#if defined (__GNUC__)
+
+/* GCC.  We assume that all compilers claiming to be GCC support sufficiently
+   many GCC attributes that the code below works.  If some non-GCC compilers
+   masquerading as GCC in fact do not implement these attributes, version checks
+   may be required.  */
+
+/* We use the _libctf_*_ pattern to avoid clashes with any future attribute
+   macros glibc may introduce, which have names of the pattern
+   __attribute_blah__.  */
+
+#define _libctf_printflike_(string_index,first_to_check) \
+    __attribute__ ((__format__ (__printf__, (string_index), (first_to_check))))
+#define _libctf_unlikely_(x) __builtin_expect ((x), 0)
+#define _libctf_unused_ __attribute__ ((__unused__))
+#define _libctf_malloc_ __attribute__((__malloc__))
+
+#endif
+
+_libctf_malloc_
+extern void *ctf_data_alloc (size_t);
+extern void ctf_data_free (void *, size_t);
+extern void ctf_data_protect (void *, size_t);
+
+_libctf_malloc_
+extern void *ctf_mmap (size_t length, size_t offset, int fd);
+extern void ctf_munmap (void *, size_t);
+extern ssize_t ctf_pread (int fd, void *buf, ssize_t count, off_t offset);
+
+_libctf_malloc_
+extern void *ctf_alloc (size_t);
+extern void ctf_free (void *);
+
+_libctf_printflike_ (1, 2)
+extern void ctf_dprintf (const char *, ...);
+extern void libctf_init_debug (void);
+
+extern int _libctf_debug;	/* debugging messages enabled */
+
+#ifdef	__cplusplus
+}
+#endif
+
+#endif /* _CTF_IMPL_H */