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The first ctf_snapshot called after CTF file creation yields a snapshot
handle that always yields a spurious ECTF_OVERROLLBACK error ("Attempt
to roll back past a ctf_update") on ctf_rollback(), even if ctf_update
has never been called.
The fix is to start with a ctf_snapshot value higher than the zero value
that ctf_snapshot_lu ("last update CTF snapshot value") is initialized
to.
libctf/
* ctf-create.c (ctf_create): Fix off-by-one error.
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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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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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Too many platforms don't support it, and we can always safely use %lu or
%li anyway, because the only uses are in debugging output.
libctf/
* ctf-archive.c (ctf_arc_write): Eschew %zi format specifier.
(ctf_arc_open_by_offset): Likewise.
* ctf-create.c (ctf_add_type): Likewise.
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On x86-64 Fedora 29, I tried to build a mingw-hosted gdb that targets
ppc-linux. You can do this with:
../binutils-gdb/configure --host=i686-w64-mingw32 --target=ppc-linux \
--disable-{binutils,gas,gold,gprof,ld}
The build failed with these errors in libctf:
In file included from ../../binutils-gdb/libctf/ctf-create.c:20:
../../binutils-gdb/libctf/ctf-create.c: In function 'ctf_add_encoded':
../../binutils-gdb/libctf/ctf-create.c:803:59: error: 'NBBY' undeclared (first use in this function)
dtd->dtd_data.ctt_size = clp2 (P2ROUNDUP (ep->cte_bits, NBBY) / NBBY);
^~~~
../../binutils-gdb/libctf/ctf-impl.h:254:42: note: in definition of macro 'P2ROUNDUP'
#define P2ROUNDUP(x, align) (-(-(x) & -(align)))
^~~~~
../../binutils-gdb/libctf/ctf-create.c:803:59: note: each undeclared identifier is reported only once for each function it appears in
dtd->dtd_data.ctt_size = clp2 (P2ROUNDUP (ep->cte_bits, NBBY) / NBBY);
^~~~
../../binutils-gdb/libctf/ctf-impl.h:254:42: note: in definition of macro 'P2ROUNDUP'
#define P2ROUNDUP(x, align) (-(-(x) & -(align)))
^~~~~
../../binutils-gdb/libctf/ctf-create.c: In function 'ctf_add_slice':
../../binutils-gdb/libctf/ctf-create.c:862:59: error: 'NBBY' undeclared (first use in this function)
dtd->dtd_data.ctt_size = clp2 (P2ROUNDUP (ep->cte_bits, NBBY) / NBBY);
^~~~
../../binutils-gdb/libctf/ctf-impl.h:254:42: note: in definition of macro 'P2ROUNDUP'
#define P2ROUNDUP(x, align) (-(-(x) & -(align)))
^~~~~
../../binutils-gdb/libctf/ctf-create.c: In function 'ctf_add_member_offset':
../../binutils-gdb/libctf/ctf-create.c:1341:21: error: 'NBBY' undeclared (first use in this function)
off += lsize * NBBY;
^~~~
../../binutils-gdb/libctf/ctf-create.c: In function 'ctf_add_type':
../../binutils-gdb/libctf/ctf-create.c:1822:16: warning: unknown conversion type character 'z' in format [-Wformat=]
ctf_dprintf ("Conflict for type %s against ID %lx: "
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../../binutils-gdb/libctf/ctf-create.c:1823:35: note: format string is defined here
"union size differs, old %zi, new %zi\n",
^
../../binutils-gdb/libctf/ctf-create.c:1822:16: warning: unknown conversion type character 'z' in format [-Wformat=]
ctf_dprintf ("Conflict for type %s against ID %lx: "
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../../binutils-gdb/libctf/ctf-create.c:1823:44: note: format string is defined here
"union size differs, old %zi, new %zi\n",
^
../../binutils-gdb/libctf/ctf-create.c:1822:16: warning: too many arguments for format [-Wformat-extra-args]
ctf_dprintf ("Conflict for type %s against ID %lx: "
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
This patch fixes the actual errors in here. I did not try to fix the
printf warnings, though I think someone ought to.
Ok?
libctf/ChangeLog
2019-06-04 Tom Tromey <tromey@adacore.com>
* ctf-create.c (ctf_add_encoded, ctf_add_slice)
(ctf_add_member_offset): Use CHAR_BIT, not NBBY.
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We cannot just look for any declaration of qsort_r, because some
operating systems have a qsort_r that has a different prototype
but which still has a pair of pointers in the right places (the last two
args are interchanged): so use AC_LINK_IFELSE to check for both
known variants of qsort_r(), and swap their args into a consistent order
in a suitable inline function. (The code for this is taken almost
unchanged from gnulib.)
(Now we are not using AC_LIBOBJ any more, we can use a better name for
the qsort_r replacement as well.)
libctf/
* qsort_r.c: Rename to...
* ctf-qsort_r.c: ... this.
(_quicksort): Define to ctf_qsort_r.
* ctf-decls.h (qsort_r): Remove.
(ctf_qsort_r): Add.
(struct ctf_qsort_arg): New, transport the real ARG and COMPAR.
(ctf_qsort_compar_thunk): Rearrange the arguments to COMPAR.
* Makefile.am (libctf_a_LIBADD): Remove.
(libctf_a_SOURCES): New, add ctf-qsort_r.c.
* ctf-archive.c (ctf_arc_write): Call ctf_qsort_r, not qsort_r.
* ctf-create.c (ctf_update): Likewise.
* configure.ac: Check for BSD versus GNU qsort_r signature.
* Makefile.in: Regenerate.
* config.h.in: Likewise.
* configure: Likewise.
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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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ctf_add_type() allows you to copy types, and all the types they depend
on, from one container to another (writable) container. This lets a
program maintaining multiple distinct containers (not in a parent-child
relationship) introduce types that depend on types in one container in
another writable one, by copying the necessary types.
libctf/
* ctf-create.c (enumcmp): New.
(enumadd): Likewise.
(membcmp): Likewise.
(membadd): Likewise.
(ctf_add_type): Likewise.
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The CTF creation process looks roughly like (error handling elided):
int err;
ctf_file_t *foo = ctf_create (&err);
ctf_id_t type = ctf_add_THING (foo, ...);
ctf_update (foo);
ctf_*write (...);
Some ctf_add_THING functions accept other type IDs as arguments,
depending on the type: cv-quals, pointers, and structure and union
members all take other types as arguments. So do 'slices', which
let you take an existing integral type and recast it as a type
with a different bitness or offset within a byte, for bitfields.
One class of THING is not a type: "variables", which are mappings
of names (in the internal string table) to types. These are mostly
useful when encoding variables that do not appear in a symbol table
but which some external user has some other way to figure out the
address of at runtime (dynamic symbol lookup or querying a VM
interpreter or something).
You can snapshot the creation process at any point: rolling back to a
snapshot deletes all types and variables added since that point.
You can make arbitrary type queries on the CTF container during the
creation process, but you must call ctf_update() first, which
translates the growing dynamic container into a static one (this uses
the CTF opening machinery, added in a later commit), which is quite
expensive. This function must also be called after adding types
and before writing the container out.
Because addition of types involves looking up existing types, we add a
little of the type lookup machinery here, as well: only enough to
look up types in dynamic containers under construction.
libctf/
* ctf-create.c: New file.
* ctf-lookup.c: New file.
include/
* ctf-api.h (zlib.h): New include.
(ctf_sect_t): New.
(ctf_sect_names_t): Likewise.
(ctf_encoding_t): Likewise.
(ctf_membinfo_t): Likewise.
(ctf_arinfo_t): Likewise.
(ctf_funcinfo_t): Likewise.
(ctf_lblinfo_t): Likewise.
(ctf_snapshot_id_t): Likewise.
(CTF_FUNC_VARARG): Likewise.
(ctf_simple_open): Likewise.
(ctf_bufopen): Likewise.
(ctf_create): Likewise.
(ctf_add_array): Likewise.
(ctf_add_const): Likewise.
(ctf_add_enum_encoded): Likewise.
(ctf_add_enum): Likewise.
(ctf_add_float): Likewise.
(ctf_add_forward): Likewise.
(ctf_add_function): Likewise.
(ctf_add_integer): Likewise.
(ctf_add_slice): Likewise.
(ctf_add_pointer): Likewise.
(ctf_add_type): Likewise.
(ctf_add_typedef): Likewise.
(ctf_add_restrict): Likewise.
(ctf_add_struct): Likewise.
(ctf_add_union): Likewise.
(ctf_add_struct_sized): Likewise.
(ctf_add_union_sized): Likewise.
(ctf_add_volatile): Likewise.
(ctf_add_enumerator): Likewise.
(ctf_add_member): Likewise.
(ctf_add_member_offset): Likewise.
(ctf_add_member_encoded): Likewise.
(ctf_add_variable): Likewise.
(ctf_set_array): Likewise.
(ctf_update): Likewise.
(ctf_snapshot): Likewise.
(ctf_rollback): Likewise.
(ctf_discard): Likewise.
(ctf_write): Likewise.
(ctf_gzwrite): Likewise.
(ctf_compress_write): Likewise.
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