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ctf.h states:
> [...] the CTF string table does not contain any duplicated strings.
Unfortunately this is entirely untrue: libctf has before now made no
attempt whatsoever to deduplicate the string table. It computes the
string table's length on the fly as it adds new strings to the dynamic
CTF file, and ctf_update() just writes each string to the table and
notes the current write position as it traverses the dynamic CTF file's
data structures and builds the final CTF buffer. There is no global
view of the strings and no deduplication.
Fix this by erasing the ctf_dtvstrlen dead-reckoning length, and adding
a new dynhash table ctf_str_atoms that maps unique strings to a list
of references to those strings: a reference is a simple uint32_t * to
some value somewhere in the under-construction CTF buffer that needs
updating to note the string offset when the strtab is laid out.
Adding a string is now a simple matter of calling ctf_str_add_ref(),
which adds a new atom to the atoms table, if one doesn't already exist,
and adding the location of the reference to this atom to the refs list
attached to the atom: this works reliably as long as one takes care to
only call ctf_str_add_ref() once the final location of the offset is
known (so you can't call it on a temporary structure and then memcpy()
that structure into place in the CTF buffer, because the ref will still
point to the old location: ctf_update() changes accordingly).
Generating the CTF string table is a matter of calling
ctf_str_write_strtab(), which counts the length and number of elements
in the atoms table using the ctf_dynhash_iter() function we just added,
populating an array of pointers into the atoms table and sorting it into
order (to help compressors), then traversing this table and emitting it,
updating the refs to each atom as we go. The only complexity here is
arranging to keep the null string at offset zero, since a lot of code in
libctf depends on being able to leave strtab references at 0 to indicate
'no name'. Once the table is constructed and the refs updated, we know
how long it is, so we can realloc() the partial CTF buffer we allocated
earlier and can copy the table on to the end of it (and purge the refs
because they're not needed any more and have been invalidated by the
realloc() call in any case).
The net effect of all this is a reduction in uncompressed strtab sizes
of about 30% (perhaps a quarter to a half of all strings across the
Linux kernel are eliminated as duplicates). Of course, duplicated
strings are highly redundant, so the space saving after compression is
only about 20%: when the other non-strtab sections are factored in, CTF
sizes shrink by about 10%.
No change in externally-visible API or file format (other than the
reduction in pointless redundancy).
libctf/
* ctf-impl.h: (struct ctf_strs_writable): New, non-const version of
struct ctf_strs.
(struct ctf_dtdef): Note that dtd_data.ctt_name is unpopulated.
(struct ctf_str_atom): New, disambiguated single string.
(struct ctf_str_atom_ref): New, points to some other location that
references this string's offset.
(struct ctf_file): New members ctf_str_atoms and ctf_str_num_refs.
Remove member ctf_dtvstrlen: we no longer track the total strlen
as we add strings.
(ctf_str_create_atoms): Declare new function in ctf-string.c.
(ctf_str_free_atoms): Likewise.
(ctf_str_add): Likewise.
(ctf_str_add_ref): Likewise.
(ctf_str_purge_refs): Likewise.
(ctf_str_write_strtab): Likewise.
(ctf_realloc): Declare new function in ctf-util.c.
* ctf-open.c (ctf_bufopen): Create the atoms table.
(ctf_file_close): Destroy it.
* ctf-create.c (ctf_update): Copy-and-free it on update. No longer
special-case the position of the parname string. Construct the
strtab by calling ctf_str_add_ref and ctf_str_write_strtab after the
rest of each buffer element is constructed, not via open-coding:
realloc the CTF buffer and append the strtab to it. No longer
maintain ctf_dtvstrlen. Sort the variable entry table later, after
strtab construction.
(ctf_copy_membnames): Remove: integrated into ctf_copy_{s,l,e}members.
(ctf_copy_smembers): Drop the string offset: call ctf_str_add_ref
after buffer element construction instead.
(ctf_copy_lmembers): Likewise.
(ctf_copy_emembers): Likewise.
(ctf_create): No longer maintain the ctf_dtvstrlen.
(ctf_dtd_delete): Likewise.
(ctf_dvd_delete): Likewise.
(ctf_add_generic): Likewise.
(ctf_add_enumerator): Likewise.
(ctf_add_member_offset): Likewise.
(ctf_add_variable): Likewise.
(membadd): Likewise.
* ctf-util.c (ctf_realloc): New, wrapper around realloc that aborts
if there are active ctf_str_num_refs.
(ctf_strraw): Move to ctf-string.c.
(ctf_strptr): Likewise.
* ctf-string.c: New file, strtab manipulation.
* Makefile.am (libctf_a_SOURCES): Add it.
* Makefile.in: Regenerate.
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There are two, ctf_dynhash_iter and ctf_dynhash_iter_remove: the latter
lets you return a nonzero value to remove the element being iterated
over.
Used in the next commit.
libctf/
* ctf-impl.h (ctf_hash_iter_f): New.
(ctf_dynhash_iter): New declaration.
(ctf_dynhash_iter_remove): New declaration.
* ctf-hash.c (ctf_dynhash_iter): Define.
(ctf_dynhash_iter_remove): Likewise.
(ctf_hashtab_traverse): New.
(ctf_hashtab_traverse_remove): Likewise.
(struct ctf_traverse_cb_arg): Likewise.
(struct ctf_traverse_remove_cb_arg): Likewise.
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This allocator has the ostensible benefit that it lets us mprotect() the
memory used for CTF storage: but in exchange for this it adds
considerable complexity, since we have to track allocation sizes
ourselves for use at freeing time, note whether the data we are storing
was ctf_data_alloc()ed or not so we know if we can safely mprotect()
it... and while the mprotect()ing has found few bugs, it *has* been the
cause of more than one due to errors in all this tracking leading to us
mprotect()ing bits of the heap and stuff like that.
We are about to start composing CTF buffers from pieces so that we can
do usage-based optimizations on the strtab. This means we need
realloc(), which needs nonportable mremap() and *more* tracking of the
*original* allocation size, and the complexity and bureaucracy of all of
this is just too high for its negligible benefits.
Drop the whole thing and just use malloc() like everyone else. It knows
better than we do when it is safe to use mmap() under the covers,
anyway.
While we're at it, don't leak the entire buffer if ctf_compress_write()
fails to compress it.
libctf/
* ctf-subr.c (_PAGESIZE): Remove.
(ctf_data_alloc): Likewise.
(ctf_data_free): Likewise.
(ctf_data_protect): Likewise.
* ctf-impl.h: Remove declarations.
* ctf-create.c (ctf_update): No longer call ctf_data_protect: use
ctf_free, not ctf_data_free.
(ctf_compress_write): Use ctf_data_alloc, not ctf_alloc. Free
the buffer again on compression error.
* ctf-open.c (ctf_set_base): No longer track the size: call
ctf_free, not ctf_data_free.
(upgrade_types): Likewise. Call ctf_alloc, not ctf_data_alloc.
(ctf_bufopen): Likewise. No longer call ctf_data_protect.
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We were missing several cases where dynhash insertion might fail, likely
due to OOM but possibly for other reasons. Pass the errors on.
libctf/
* ctf-create.c (ctf_dtd_insert): Pass on error returns from
ctf_dynhash_insert.
(ctf_dvd_insert): Likewise.
(ctf_add_generic): Likewise.
(ctf_add_variable): Likewise.
* ctf-impl.h: Adjust declarations.
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- Use of nonportable <endian.h>
- Use of qsort_r
- Use of zlib without appropriate magic to pull in the binutils zlib
- Use of off64_t without checking (fixed by dropping the unused fields
that need off64_t entirely)
- signedness problems due to long being too short a type on 32-bit
platforms: ctf_id_t is now 'unsigned long', and CTF_ERR must be
used only for functions that return ctf_id_t
- One lingering use of bzero() and of <sys/errno.h>
All fixed, using code from gnulib where possible.
Relatedly, set cts_size in a couple of places it was missed
(string table and symbol table loading upon ctf_bfdopen()).
binutils/
* objdump.c (make_ctfsect): Drop cts_type, cts_flags, and
cts_offset.
* readelf.c (shdr_to_ctf_sect): Likewise.
include/
* ctf-api.h (ctf_sect_t): Drop cts_type, cts_flags, and cts_offset.
(ctf_id_t): This is now an unsigned type.
(CTF_ERR): Cast it to ctf_id_t. Note that it should only be used
for ctf_id_t-returning functions.
libctf/
* Makefile.am (ZLIB): New.
(ZLIBINC): Likewise.
(AM_CFLAGS): Use them.
(libctf_a_LIBADD): New, for LIBOBJS.
* configure.ac: Check for zlib, endian.h, and qsort_r.
* ctf-endian.h: New, providing htole64 and le64toh.
* swap.h: Code style fixes.
(bswap_identity_64): New.
* qsort_r.c: New, from gnulib (with one added #include).
* ctf-decls.h: New, providing a conditional qsort_r declaration,
and unconditional definitions of MIN and MAX.
* ctf-impl.h: Use it. Do not use <sys/errno.h>.
(ctf_set_errno): Now returns unsigned long.
* ctf-util.c (ctf_set_errno): Adjust here too.
* ctf-archive.c: Use ctf-endian.h.
(ctf_arc_open_by_offset): Use memset, not bzero. Drop cts_type,
cts_flags and cts_offset.
(ctf_arc_write): Drop debugging dependent on the size of off_t.
* ctf-create.c: Provide a definition of roundup if not defined.
(ctf_create): Drop cts_type, cts_flags and cts_offset.
(ctf_add_reftype): Do not check if type IDs are below zero.
(ctf_add_slice): Likewise.
(ctf_add_typedef): Likewise.
(ctf_add_member_offset): Cast error-returning ssize_t's to size_t
when known error-free. Drop CTF_ERR usage for functions returning
int.
(ctf_add_member_encoded): Drop CTF_ERR usage for functions returning
int.
(ctf_add_variable): Likewise.
(enumcmp): Likewise.
(enumadd): Likewise.
(membcmp): Likewise.
(ctf_add_type): Likewise. Cast error-returning ssize_t's to size_t
when known error-free.
* ctf-dump.c (ctf_is_slice): Drop CTF_ERR usage for functions
returning int: use CTF_ERR for functions returning ctf_type_id.
(ctf_dump_label): Likewise.
(ctf_dump_objts): Likewise.
* ctf-labels.c (ctf_label_topmost): Likewise.
(ctf_label_iter): Likewise.
(ctf_label_info): Likewise.
* ctf-lookup.c (ctf_func_args): Likewise.
* ctf-open.c (upgrade_types): Cast to size_t where appropriate.
(ctf_bufopen): Likewise. Use zlib types as needed.
* ctf-types.c (ctf_member_iter): Drop CTF_ERR usage for functions
returning int.
(ctf_enum_iter): Likewise.
(ctf_type_size): Likewise.
(ctf_type_align): Likewise. Cast to size_t where appropriate.
(ctf_type_kind_unsliced): Likewise.
(ctf_type_kind): Likewise.
(ctf_type_encoding): Likewise.
(ctf_member_info): Likewise.
(ctf_array_info): Likewise.
(ctf_enum_value): Likewise.
(ctf_type_rvisit): Likewise.
* ctf-open-bfd.c (ctf_bfdopen): Drop cts_type, cts_flags and
cts_offset.
(ctf_simple_open): Likewise.
(ctf_bfdopen_ctfsect): Likewise. Set cts_size properly.
* Makefile.in: Regenerate.
* aclocal.m4: Likewise.
* config.h: Likewise.
* configure: Likewise.
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This old Solaris standard allows callers to specify that they are
expecting one particular API and/or CTF file format from the library.
libctf/
* ctf-impl.h (_libctf_version): New declaration.
* ctf-subr.c (_libctf_version): Define it.
(ctf_version): New.
include/
* ctf-api.h (ctf_version): New.
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These functions allow you to look up types given a name in a simple
subset of C declarator syntax (no function pointers), to look up the
types of variables given a name, and to look up the types of data
objects and the type signatures of functions given symbol table offsets.
(Despite its name, one function in this commit, ctf_lookup_symbol_name(),
is for the internal use of libctf only, and does not appear in any
public header files.)
libctf/
* ctf-lookup.c (isqualifier): New.
(ctf_lookup_by_name): Likewise.
(struct ctf_lookup_var_key): Likewise.
(ctf_lookup_var): Likewise.
(ctf_lookup_variable): Likewise.
(ctf_lookup_symbol_name): Likewise.
(ctf_lookup_by_symbol): Likewise.
(ctf_func_info): Likewise.
(ctf_func_args): Likewise.
include/
* ctf-api.h (ctf_func_info): New.
(ctf_func_args): Likewise.
(ctf_lookup_by_symbol): Likewise.
(ctf_lookup_by_symbol): Likewise.
(ctf_lookup_variable): Likewise.
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Finally we get to the functions used to actually look up and enumerate
properties of types in a container (names, sizes, members, what type a
pointer or cv-qual references, determination of whether two types are
assignment-compatible, etc).
With a very few exceptions these do not work for types newly added via
ctf_add_*(): they only work on types in read-only containers, or types
added before the most recent call to ctf_update().
This also adds support for lookup of "variables" (string -> type ID
mappings) and for generation of C type names corresponding to a type ID.
libctf/
* ctf-decl.c: New file.
* ctf-types.c: Likewise.
* ctf-impl.h: New declarations.
include/
* ctf-api.h (ctf_visit_f): New definition.
(ctf_member_f): Likewise.
(ctf_enum_f): Likewise.
(ctf_variable_f): Likewise.
(ctf_type_f): Likewise.
(ctf_type_isparent): Likewise.
(ctf_type_ischild): Likewise.
(ctf_type_resolve): Likewise.
(ctf_type_aname): Likewise.
(ctf_type_lname): Likewise.
(ctf_type_name): Likewise.
(ctf_type_sizee): Likewise.
(ctf_type_align): Likewise.
(ctf_type_kind): Likewise.
(ctf_type_reference): Likewise.
(ctf_type_pointer): Likewise.
(ctf_type_encoding): Likewise.
(ctf_type_visit): Likewise.
(ctf_type_cmp): Likewise.
(ctf_type_compat): Likewise.
(ctf_member_info): Likewise.
(ctf_array_info): Likewise.
(ctf_enum_name): Likewise.
(ctf_enum_value): Likewise.
(ctf_member_iter): Likewise.
(ctf_enum_iter): Likewise.
(ctf_type_iter): Likewise.
(ctf_variable_iter): Likewise.
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These functions let you open an ELF file with a customarily-named CTF
section in it, automatically opening the CTF file or archive and
associating the symbol and string tables in the ELF file with the CTF
container, so that you can look up the types of symbols in the ELF file
via ctf_lookup_by_symbol(), and so that strings can be shared between
the ELF file and CTF container, to save space.
It uses BFD machinery to do so. This has now been lightly tested and
seems to work. In particular, if you already have a bfd you can pass
it in to ctf_bfdopen(), and if you want a bfd made for you you can
call ctf_open() or ctf_fdopen(), optionally specifying a target (or
try once without a target and then again with one if you get
ECTF_BFD_AMBIGUOUS back).
We use a forward declaration for the struct bfd in ctf-api.h, so that
ctf-api.h users are not required to pull in <bfd.h>. (This is mostly
for the sake of readelf.)
libctf/
* ctf-open-bfd.c: New file.
* ctf-open.c (ctf_close): New.
* ctf-impl.h: Include bfd.h.
(ctf_file): New members ctf_data_mmapped, ctf_data_mmapped_len.
(ctf_archive_internal): New members ctfi_abfd, ctfi_data,
ctfi_bfd_close.
(ctf_bfdopen_ctfsect): New declaration.
(_CTF_SECTION): likewise.
include/
* ctf-api.h (struct bfd): New forward.
(ctf_fdopen): New.
(ctf_bfdopen): Likewise.
(ctf_open): Likewise.
(ctf_arc_open): Likewise.
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If you need to store a large number of CTF containers somewhere, this
provides a dedicated facility for doing so: an mmappable archive format
like a very simple tar or ar without all the system-dependent format
horrors or need for heavy file copying, with built-in compression of
files above a particular size threshold.
libctf automatically mmap()s uncompressed elements of these archives, or
uncompresses them, as needed. (If the platform does not support mmap(),
copying into dynamically-allocated buffers is used.)
Archive iteration operations are partitioned into raw and non-raw
forms. Raw operations pass thhe raw archive contents to the callback:
non-raw forms open each member with ctf_bufopen() and pass the resulting
ctf_file_t to the iterator instead. This lets you manipulate the raw
data in the archive, or the contents interpreted as a CTF file, as
needed.
It is not yet known whether we will store CTF archives in a linked ELF
object in one of these (akin to debugdata) or whether they'll get one
section per TU plus one parent container for types shared between them.
(In the case of ELF objects with very large numbers of TUs, an archive
of all of them would seem preferable, so we might just use an archive,
and add lzma support so you can assume that .gnu_debugdata and .ctf are
compressed using the same algorithm if both are present.)
To make usage easier, the ctf_archive_t is not the on-disk
representation but an abstraction over both ctf_file_t's and archives of
many ctf_file_t's: users see both CTF archives and raw CTF files as
ctf_archive_t's upon opening, the only difference being that a raw CTF
file has only a single "archive member", named ".ctf" (the default if a
null pointer is passed in as the name). The next commit will make use
of this facility, in addition to providing the public interface to
actually open archives. (In the future, it should be possible to have
all CTF sections in an ELF file appear as an "archive" in the same
fashion.)
This machinery is also used to allow library-internal creators of
ctf_archive_t's (such as the next commit) to stash away an ELF string
and symbol table, so that all opens of members in a given archive will
use them. This lets CTF archives exploit the ELF string and symbol
table just like raw CTF files can.
(All this leads to somewhat confusing type naming. The ctf_archive_t is
a typedef for the opaque internal type, struct ctf_archive_internal: the
non-internal "struct ctf_archive" is the on-disk structure meant for
other libraries manipulating CTF files. It is probably clearest to use
the struct name for struct ctf_archive_internal inside the program, and
the typedef names outside.)
libctf/
* ctf-archive.c: New.
* ctf-impl.h (ctf_archive_internal): New type.
(ctf_arc_open_internal): New declaration.
(ctf_arc_bufopen): Likewise.
(ctf_arc_close_internal): Likewise.
include/
* ctf.h (CTFA_MAGIC): New.
(struct ctf_archive): New.
(struct ctf_archive_modent): Likewise.
* ctf-api.h (ctf_archive_member_f): New.
(ctf_archive_raw_member_f): Likewise.
(ctf_arc_write): Likewise.
(ctf_arc_close): Likewise.
(ctf_arc_open_by_name): Likewise.
(ctf_archive_iter): Likewise.
(ctf_archive_raw_iter): Likewise.
(ctf_get_arc): Likewise.
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We now enter a series of commits that are sufficiently tangled that
avoiding forward definitions is almost impossible: no attempt is made to
make individual commits compilable (which is why the build system does
not reference any of them yet): the only important thing is that they
should form something like conceptual groups.
But first, some definitions, including the core ctf_file_t itself. Uses
of these definitions will be introduced in later commits.
libctf/
* ctf-impl.h: New definitions and declarations for type creation
and lookup.
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libctf maintains two distinct hash ADTs, one (ctf_dynhash) for wrapping
dynamically-generated unknown-sized hashes during CTF file construction,
one (ctf_hash) for wrapping unchanging hashes whose size is known at
creation time for reading CTF files that were previously created.
In the binutils implementation, these are both fairly thin wrappers
around libiberty hashtab.
Unusually, this code is not kept synchronized with libdtrace-ctf,
due to its dependence on libiberty hashtab.
libctf/
* ctf-hash.c: New file.
* ctf-impl.h: New declarations.
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These utilities are a bit of a ragbag of small things needed by more
than one TU: list manipulation, ELF32->64 translators, routines to look
up strings in string tables, dynamically-allocated string appenders, and
routines to set the specialized errno values previously committed in
<ctf-api.h>.
We do still need to dig around in raw ELF symbol tables in places,
because libctf allows the caller to pass in the contents of string and
symbol sections without telling it where they come from, so we cannot
use BFD to get the symbols (BFD reasonably demands the entire file). So
extract minimal ELF definitions from glibc into a private header named
libctf/elf.h: later, we use those to get symbols. (The start-of-
copyright range on elf.h reflects this glibc heritage.)
libctf/
* ctf-util.c: New file.
* elf.h: Likewise.
* ctf-impl.h: Include it, and add declarations.
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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.
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