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binutils-gdb/libctf/ctf-util.c
Nick Alcock 688d28f621 libctf, next: introduce new class of easier-to-use iterators 
The libctf machinery currently only provides one way to iterate over its
data structures: ctf_*_iter functions that take a callback and an arg
and repeatedly call it.

This *works*, but if you are doing a lot of iteration it is really quite
inconvenient: you have to package up your local variables into
structures over and over again and spawn lots of little functions even
if it would be clearer in a single run of code.  Look at ctf-string.c
for an extreme example of how unreadable this can get, with
three-line-long functions proliferating wildly.

The deduplicator takes this to the Nth level. It iterates over a whole
bunch of things: if we'd had to use _iter-class iterators for all of
them there would be twenty additional functions in the deduplicator
alone, for no other reason than that the iterator API requires it.

Let's do something better. strtok_r gives us half the design: generators
in a number of other languages give us the other half.

The *_next API allows you to iterate over CTF-like entities in a single
function using a normal while loop. e.g. here we are iterating over all
the types in a dict:

ctf_next_t *i = NULL;
int *hidden;
ctf_id_t id;

while ((id = ctf_type_next (fp, &i, &hidden, 1)) != CTF_ERR)
  {
    /* do something with 'hidden' and 'id' */
  }
if (ctf_errno (fp) != ECTF_NEXT_END)
    /* iteration error */

Here we are walking through the members of a struct with CTF ID
'struct_type':

ctf_next_t *i = NULL;
ssize_t offset;
const char *name;
ctf_id_t membtype;

while ((offset = ctf_member_next (fp, struct_type, &i, &name,
                                  &membtype)) >= 0
  {
    /* do something with offset, name, and membtype */
  }
if (ctf_errno (fp) != ECTF_NEXT_END)
    /* iteration error */

Like every other while loop, this means you have access to all the local
variables outside the loop while inside it, with no need to tiresomely
package things up in structures, move the body of the loop into a
separate function, etc, as you would with an iterator taking a callback.

ctf_*_next allocates 'i' for you on first entry (when it must be NULL),
and frees and NULLs it and returns a _next-dependent flag value when the
iteration is over: the fp errno is set to ECTF_NEXT_END when the
iteartion ends normally.  If you want to exit early, call
ctf_next_destroy on the iterator.  You can copy iterators using
ctf_next_copy, which copies their current iteration position so you can
remember loop positions and go back to them later (or ctf_next_destroy
them if you don't need them after all).

Each _next function returns an always-likely-to-be-useful property of
the thing being iterated over, and takes pointers to parameters for the
others: with very few exceptions all those parameters can be NULLs if
you're not interested in them, so e.g. you can iterate over only the
offsets of members of a structure this way:

while ((offset = ctf_member_next (fp, struct_id, &i, NULL, NULL)) >= 0)

If you pass an iterator in use by one iteration function to another one,
you get the new error ECTF_NEXT_WRONGFUN back; if you try to change
ctf_file_t in mid-iteration, you get ECTF_NEXT_WRONGFP back.

Internally the ctf_next_t remembers the iteration function in use,
various sizes and increments useful for almost all iterations, then
uses unions to overlap the actual entities being iterated over to keep
ctf_next_t size down.

Iterators available in the public API so far (all tested in actual use
in the deduplicator):

/* Iterate over the members of a STRUCT or UNION, returning each member's
   offset and optionally name and member type in turn.  On end-of-iteration,
   returns -1.  */
ssize_t
ctf_member_next (ctf_file_t *fp, ctf_id_t type, ctf_next_t **it,
                 const char **name, ctf_id_t *membtype);

/* Iterate over the members of an enum TYPE, returning each enumerand's
   NAME or NULL at end of iteration or error, and optionally passing
   back the enumerand's integer VALue.  */
const char *
ctf_enum_next (ctf_file_t *fp, ctf_id_t type, ctf_next_t **it,
              int *val);

/* Iterate over every type in the given CTF container (not including
   parents), optionally including non-user-visible types, returning
   each type ID and optionally the hidden flag in turn. Returns CTF_ERR
   on end of iteration or error.  */
ctf_id_t
ctf_type_next (ctf_file_t *fp, ctf_next_t **it, int *flag,
               int want_hidden);

/* Iterate over every variable in the given CTF container, in arbitrary
   order, returning the name and type of each variable in turn.  The
   NAME argument is not optional.  Returns CTF_ERR on end of iteration
   or error.  */
ctf_id_t
ctf_variable_next (ctf_file_t *fp, ctf_next_t **it, const char **name);

/* Iterate over all CTF files in an archive, returning each dict in turn as a
   ctf_file_t, and NULL on error or end of iteration.  It is the caller's
   responsibility to close it.  Parent dicts may be skipped.  Regardless of
   whether they are skipped or not, the caller must ctf_import the parent if
   need be.  */
ctf_file_t *
ctf_archive_next (const ctf_archive_t *wrapper, ctf_next_t **it,
                  const char **name, int skip_parent, int *errp);

ctf_label_next is prototyped but not implemented yet.

include/
	* ctf-api.h (ECTF_NEXT_END): New error.
	(ECTF_NEXT_WRONGFUN): Likewise.
	(ECTF_NEXT_WRONGFP): Likewise.
	(ECTF_NERR): Adjust.
	(ctf_next_t): New.
	(ctf_next_create): New prototype.
	(ctf_next_destroy): Likewise.
	(ctf_next_copy): Likewise.
	(ctf_member_next): Likewise.
	(ctf_enum_next): Likewise.
	(ctf_type_next): Likewise.
	(ctf_label_next): Likewise.
	(ctf_variable_next): Likewise.

libctf/
	* ctf-impl.h (ctf_next): New.
	(ctf_get_dict): New prototype.
	* ctf-lookup.c (ctf_get_dict): New, split out of...
	(ctf_lookup_by_id): ... here.
	* ctf-util.c (ctf_next_create): New.
	(ctf_next_destroy): New.
	(ctf_next_copy): New.
	* ctf-types.c (includes): Add <assert.h>.
	(ctf_member_next): New.
	(ctf_enum_next): New.
	(ctf_type_iter): Document the lack of iteration over parent
	types.
	(ctf_type_next): New.
	(ctf_variable_next): New.
	* ctf-archive.c (ctf_archive_next): New.
	* libctf.ver: Add new public functions.
2020-07-22 17:57:50 +01:00

205 lines
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/* Miscellaneous utilities.
Copyright (C) 2019-2020 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/>. */
#include <ctf-impl.h>
#include <string.h>
/* Simple doubly-linked list append routine. This implementation assumes that
each list element contains an embedded ctf_list_t as the first member.
An additional ctf_list_t is used to store the head (l_next) and tail
(l_prev) pointers. The current head and tail list elements have their
previous and next pointers set to NULL, respectively. */
void
ctf_list_append (ctf_list_t *lp, void *newp)
{
ctf_list_t *p = lp->l_prev; /* p = tail list element. */
ctf_list_t *q = newp; /* q = new list element. */
lp->l_prev = q;
q->l_prev = p;
q->l_next = NULL;
if (p != NULL)
p->l_next = q;
else
lp->l_next = q;
}
/* Prepend the specified existing element to the given ctf_list_t. The
existing pointer should be pointing at a struct with embedded ctf_list_t. */
void
ctf_list_prepend (ctf_list_t * lp, void *newp)
{
ctf_list_t *p = newp; /* p = new list element. */
ctf_list_t *q = lp->l_next; /* q = head list element. */
lp->l_next = p;
p->l_prev = NULL;
p->l_next = q;
if (q != NULL)
q->l_prev = p;
else
lp->l_prev = p;
}
/* Delete the specified existing element from the given ctf_list_t. The
existing pointer should be pointing at a struct with embedded ctf_list_t. */
void
ctf_list_delete (ctf_list_t *lp, void *existing)
{
ctf_list_t *p = existing;
if (p->l_prev != NULL)
p->l_prev->l_next = p->l_next;
else
lp->l_next = p->l_next;
if (p->l_next != NULL)
p->l_next->l_prev = p->l_prev;
else
lp->l_prev = p->l_prev;
}
/* Return 1 if the list is empty. */
int
ctf_list_empty_p (ctf_list_t *lp)
{
return (lp->l_next == NULL && lp->l_prev == NULL);
}
/* Convert a 32-bit ELF symbol into Elf64 and return a pointer to it. */
Elf64_Sym *
ctf_sym_to_elf64 (const Elf32_Sym *src, Elf64_Sym *dst)
{
dst->st_name = src->st_name;
dst->st_value = src->st_value;
dst->st_size = src->st_size;
dst->st_info = src->st_info;
dst->st_other = src->st_other;
dst->st_shndx = src->st_shndx;
return dst;
}
/* A string appender working on dynamic strings. Returns NULL on OOM. */
char *
ctf_str_append (char *s, const char *append)
{
size_t s_len = 0;
if (append == NULL)
return s;
if (s != NULL)
s_len = strlen (s);
size_t append_len = strlen (append);
if ((s = realloc (s, s_len + append_len + 1)) == NULL)
return NULL;
memcpy (s + s_len, append, append_len);
s[s_len + append_len] = '\0';
return s;
}
/* A version of ctf_str_append that returns the old string on OOM. */
char *
ctf_str_append_noerr (char *s, const char *append)
{
char *new_s;
new_s = ctf_str_append (s, append);
if (!new_s)
return s;
return new_s;
}
/* A realloc() that fails noisily if called with any ctf_str_num_users. */
void *
ctf_realloc (ctf_file_t *fp, void *ptr, size_t size)
{
if (fp->ctf_str_num_refs > 0)
{
ctf_dprintf ("%p: attempt to realloc() string table with %lu active refs\n",
(void *) fp, (unsigned long) fp->ctf_str_num_refs);
return NULL;
}
return realloc (ptr, size);
}
/* Store the specified error code into errp if it is non-NULL, and then
return NULL for the benefit of the caller. */
void *
ctf_set_open_errno (int *errp, int error)
{
if (errp != NULL)
*errp = error;
return NULL;
}
/* Store the specified error code into the CTF container, and then return
CTF_ERR / -1 for the benefit of the caller. */
unsigned long
ctf_set_errno (ctf_file_t * fp, int err)
{
fp->ctf_errno = err;
return CTF_ERR;
}
/* Create a ctf_next_t. */
ctf_next_t *
ctf_next_create (void)
{
return calloc (1, sizeof (struct ctf_next));
}
/* Destroy a ctf_next_t, for early exit from iterators. */
void
ctf_next_destroy (ctf_next_t *i)
{
free (i);
}
/* Copy a ctf_next_t. */
ctf_next_t *
ctf_next_copy (ctf_next_t *i)
{
ctf_next_t *i2;
if ((i2 = ctf_next_create()) == NULL)
return NULL;
memcpy (i2, i, sizeof (struct ctf_next));
return i2;
}
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