2023-01-01 20:49:04 +08:00
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/* Copyright (C) 2017-2023 Free Software Foundation, Inc.
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Introduce gdb::byte_vector, add allocator that default-initializes
In some cases we've been replacing heap-allocated gdb_byte buffers
managed with xmalloc/make_cleanup(xfree) with gdb::vector<gdb_byte>.
That usually pessimizes the code a little bit because std::vector
value-initializes elements (which for gdb_byte means
zero-initialization), while if you're creating a temporary buffer,
you're most certaintly going to fill it in with some data. An
alternative is to use
unique_ptr<gdb_byte[]> buf (new gdb_byte[size]);
but it looks like that's not very popular.
Recently, a use of obstacks in dwarf2read.c was replaced with
std::vector<gdb_byte> and that as well introduced a pessimization for
always memsetting the buffer when it's garanteed that the zeros will
be overwritten immediately. (see dwarf2read.c change in this patch to
find it.)
So here's a different take at addressing this issue "by design":
#1 - Introduce default_init_allocator<T>
I.e., a custom allocator that does default construction using default
initialization, meaning, no more zero initialization. That's the
default_init_allocation<T> class added in this patch.
See "Notes" at
<http://en.cppreference.com/w/cpp/container/vector/resize>.
#2 - Introduce def_vector<T>
I.e., a convenience typedef, because typing the allocator is annoying:
using def_vector<T> = std::vector<T, gdb::default_init_allocator<T>>;
#3 - Introduce byte_vector
Because gdb_byte vectors will be the common thing, add a convenience
"byte_vector" typedef:
using byte_vector = def_vector<gdb_byte>;
which is really the same as:
std::vector<gdb_byte, gdb::default_init_allocator<gdb_byte>>;
The intent then is to make "gdb::byte_vector" be the go-to for dynamic
byte buffers. So the less friction, the better.
#4 - Adjust current code to use it.
To set the example going forward. Replace std::vector uses and also
unique_ptr<byte[]> uses.
One nice thing is that with this allocator, for changes like these:
-std::unique_ptr<byte[]> buf (new gdb_byte[some_size]);
+gdb::byte_vector buf (some_size);
fill_with_data (buf.data (), buf.size ());
the generated code is the same as before. I.e., the compiler
de-structures the vector and gets rid of the unused "reserved vs size"
related fields.
The other nice thing is that it's easier to write
gdb::byte_vector buf (size);
than
std::unique_ptr<gdb_byte[]> buf (new gdb_byte[size]);
or even (C++14):
auto buf = std::make_unique<gdb_byte[]> (size); // zero-initializes...
#5 - Suggest s/std::vector<gdb_byte>/gdb::byte_vector/ going forward.
Note that this commit actually fixes a couple of bugs where the current
code is incorrectly using "std::vector::reserve(new_size)" and then
accessing the vector's internal buffer beyond the vector's size: see
dwarf2loc.c and charset.c. That's undefined behavior and may trigger
debug mode assertion failures. With default_init_allocator,
"resize()" behaves like "reserve()" performance wise, in that it
leaves new elements with unspecified values, but, it does that safely
without triggering undefined behavior when you access those values.
gdb/ChangeLog:
2017-06-14 Pedro Alves <palves@redhat.com>
* ada-lang.c: Include "common/byte-vector.h".
(ada_value_primitive_packed_val): Use gdb::byte_vector.
* charset.c (wchar_iterator::iterate): Resize the vector instead
of reserving it.
* common/byte-vector.h: Include "common/def-vector.h".
(wchar_iterator::m_out): Now a gdb::def_vector<gdb_wchar_t>.
* cli/cli-dump.c: Include "common/byte-vector.h".
(dump_memory_to_file, restore_binary_file): Use gdb::byte_vector.
* common/byte-vector.h: New file.
* common/def-vector.h: New file.
* common/default-init-alloc.h: New file.
* dwarf2loc.c: Include "common/byte-vector.h".
(rw_pieced_value): Use gdb::byte_vector, and resize the vector
instead of reserving it.
* dwarf2read.c: Include "common/byte-vector.h".
(data_buf::m_vec): Now a gdb::byte_vector.
* gdb_regex.c: Include "common/def-vector.h".
(compiled_regex::compiled_regex): Use gdb::def_vector<char>.
* mi/mi-main.c: Include "common/byte-vector.h".
(mi_cmd_data_read_memory): Use gdb::byte_vector.
* printcmd.c: Include "common/byte-vector.h".
(print_scalar_formatted): Use gdb::byte_vector.
* valprint.c: Include "common/byte-vector.h".
(maybe_negate_by_bytes, print_decimal_chars): Use
gdb::byte_vector.
2017-06-14 18:08:52 +08:00
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This file is part of GDB.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>. */
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#ifndef COMMON_BYTE_VECTOR_H
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#define COMMON_BYTE_VECTOR_H
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Rename common to gdbsupport
This is the next patch in the ongoing series to move gdbsever to the
top level.
This patch just renames the "common" directory. The idea is to do
this move in two parts: first rename the directory (this patch), then
move the directory to the top. This approach makes the patches a bit
more tractable.
I chose the name "gdbsupport" for the directory. However, as this
patch was largely written by sed, we could pick a new name without too
much difficulty.
Tested by the buildbot.
gdb/ChangeLog
2019-07-09 Tom Tromey <tom@tromey.com>
* contrib/ari/gdb_ari.sh: Change common to gdbsupport.
* configure: Rebuild.
* configure.ac: Change common to gdbsupport.
* gdbsupport: Rename from common.
* acinclude.m4: Change common to gdbsupport.
* Makefile.in (CONFIG_SRC_SUBDIR, COMMON_SFILES)
(HFILES_NO_SRCDIR, stamp-version, ALLDEPFILES): Change common to
gdbsupport.
* aarch64-tdep.c, ada-lang.c, ada-lang.h, agent.c, alloc.c,
amd64-darwin-tdep.c, amd64-dicos-tdep.c, amd64-fbsd-nat.c,
amd64-fbsd-tdep.c, amd64-linux-nat.c, amd64-linux-tdep.c,
amd64-nbsd-tdep.c, amd64-obsd-tdep.c, amd64-sol2-tdep.c,
amd64-tdep.c, amd64-windows-tdep.c, arch-utils.c,
arch/aarch64-insn.c, arch/aarch64.c, arch/aarch64.h, arch/amd64.c,
arch/amd64.h, arch/arm-get-next-pcs.c, arch/arm-linux.c,
arch/arm.c, arch/i386.c, arch/i386.h, arch/ppc-linux-common.c,
arch/riscv.c, arch/riscv.h, arch/tic6x.c, arm-tdep.c, auto-load.c,
auxv.c, ax-gdb.c, ax-general.c, ax.h, breakpoint.c, breakpoint.h,
btrace.c, btrace.h, build-id.c, build-id.h, c-lang.h, charset.c,
charset.h, cli/cli-cmds.c, cli/cli-cmds.h, cli/cli-decode.c,
cli/cli-dump.c, cli/cli-option.h, cli/cli-script.c,
coff-pe-read.c, command.h, compile/compile-c-support.c,
compile/compile-c.h, compile/compile-cplus-symbols.c,
compile/compile-cplus-types.c, compile/compile-cplus.h,
compile/compile-loc2c.c, compile/compile.c, completer.c,
completer.h, contrib/ari/gdb_ari.sh, corefile.c, corelow.c,
cp-support.c, cp-support.h, cp-valprint.c, csky-tdep.c, ctf.c,
darwin-nat.c, debug.c, defs.h, disasm-selftests.c, disasm.c,
disasm.h, dtrace-probe.c, dwarf-index-cache.c,
dwarf-index-cache.h, dwarf-index-write.c, dwarf2-frame.c,
dwarf2expr.c, dwarf2loc.c, dwarf2read.c, event-loop.c,
event-top.c, exceptions.c, exec.c, extension.h, fbsd-nat.c,
features/aarch64-core.c, features/aarch64-fpu.c,
features/aarch64-pauth.c, features/aarch64-sve.c,
features/i386/32bit-avx.c, features/i386/32bit-avx512.c,
features/i386/32bit-core.c, features/i386/32bit-linux.c,
features/i386/32bit-mpx.c, features/i386/32bit-pkeys.c,
features/i386/32bit-segments.c, features/i386/32bit-sse.c,
features/i386/64bit-avx.c, features/i386/64bit-avx512.c,
features/i386/64bit-core.c, features/i386/64bit-linux.c,
features/i386/64bit-mpx.c, features/i386/64bit-pkeys.c,
features/i386/64bit-segments.c, features/i386/64bit-sse.c,
features/i386/x32-core.c, features/riscv/32bit-cpu.c,
features/riscv/32bit-csr.c, features/riscv/32bit-fpu.c,
features/riscv/64bit-cpu.c, features/riscv/64bit-csr.c,
features/riscv/64bit-fpu.c, features/tic6x-c6xp.c,
features/tic6x-core.c, features/tic6x-gp.c, filename-seen-cache.h,
findcmd.c, findvar.c, fork-child.c, gcore.c, gdb_bfd.c, gdb_bfd.h,
gdb_proc_service.h, gdb_regex.c, gdb_select.h, gdb_usleep.c,
gdbarch-selftests.c, gdbthread.h, gdbtypes.h, gnu-nat.c,
go32-nat.c, guile/guile.c, guile/scm-ports.c,
guile/scm-safe-call.c, guile/scm-type.c, i386-fbsd-nat.c,
i386-fbsd-tdep.c, i386-go32-tdep.c, i386-linux-nat.c,
i386-linux-tdep.c, i386-tdep.c, i387-tdep.c,
ia64-libunwind-tdep.c, ia64-linux-nat.c, inf-child.c,
inf-ptrace.c, infcall.c, infcall.h, infcmd.c, inferior-iter.h,
inferior.c, inferior.h, inflow.c, inflow.h, infrun.c, infrun.h,
inline-frame.c, language.h, linespec.c, linux-fork.c, linux-nat.c,
linux-tdep.c, linux-thread-db.c, location.c, machoread.c,
macrotab.h, main.c, maint.c, maint.h, memattr.c, memrange.h,
mi/mi-cmd-break.h, mi/mi-cmd-env.c, mi/mi-cmd-stack.c,
mi/mi-cmd-var.c, mi/mi-interp.c, mi/mi-main.c, mi/mi-parse.h,
minsyms.c, mips-linux-tdep.c, namespace.h,
nat/aarch64-linux-hw-point.c, nat/aarch64-linux-hw-point.h,
nat/aarch64-linux.c, nat/aarch64-sve-linux-ptrace.c,
nat/amd64-linux-siginfo.c, nat/fork-inferior.c,
nat/linux-btrace.c, nat/linux-btrace.h, nat/linux-namespaces.c,
nat/linux-nat.h, nat/linux-osdata.c, nat/linux-personality.c,
nat/linux-procfs.c, nat/linux-ptrace.c, nat/linux-ptrace.h,
nat/linux-waitpid.c, nat/mips-linux-watch.c,
nat/mips-linux-watch.h, nat/ppc-linux.c, nat/x86-dregs.c,
nat/x86-dregs.h, nat/x86-linux-dregs.c, nat/x86-linux.c,
nto-procfs.c, nto-tdep.c, objfile-flags.h, objfiles.c, objfiles.h,
obsd-nat.c, observable.h, osdata.c, p-valprint.c, parse.c,
parser-defs.h, ppc-linux-nat.c, printcmd.c, probe.c, proc-api.c,
procfs.c, producer.c, progspace.h, psymtab.h,
python/py-framefilter.c, python/py-inferior.c, python/py-ref.h,
python/py-type.c, python/python.c, record-btrace.c, record-full.c,
record.c, record.h, regcache-dump.c, regcache.c, regcache.h,
remote-fileio.c, remote-fileio.h, remote-sim.c, remote.c,
riscv-tdep.c, rs6000-aix-tdep.c, rust-exp.y, s12z-tdep.c,
selftest-arch.c, ser-base.c, ser-event.c, ser-pipe.c, ser-tcp.c,
ser-unix.c, skip.c, solib-aix.c, solib-target.c, solib.c,
source-cache.c, source.c, source.h, sparc-nat.c, spu-linux-nat.c,
stack.c, stap-probe.c, symfile-add-flags.h, symfile.c, symfile.h,
symtab.c, symtab.h, target-descriptions.c, target-descriptions.h,
target-memory.c, target.c, target.h, target/waitstatus.c,
target/waitstatus.h, thread-iter.h, thread.c, tilegx-tdep.c,
top.c, top.h, tracefile-tfile.c, tracefile.c, tracepoint.c,
tracepoint.h, tui/tui-io.c, ui-file.c, ui-out.h,
unittests/array-view-selftests.c,
unittests/child-path-selftests.c, unittests/cli-utils-selftests.c,
unittests/common-utils-selftests.c,
unittests/copy_bitwise-selftests.c, unittests/environ-selftests.c,
unittests/format_pieces-selftests.c,
unittests/function-view-selftests.c,
unittests/lookup_name_info-selftests.c,
unittests/memory-map-selftests.c, unittests/memrange-selftests.c,
unittests/mkdir-recursive-selftests.c,
unittests/observable-selftests.c,
unittests/offset-type-selftests.c, unittests/optional-selftests.c,
unittests/parse-connection-spec-selftests.c,
unittests/ptid-selftests.c, unittests/rsp-low-selftests.c,
unittests/scoped_fd-selftests.c,
unittests/scoped_mmap-selftests.c,
unittests/scoped_restore-selftests.c,
unittests/string_view-selftests.c, unittests/style-selftests.c,
unittests/tracepoint-selftests.c, unittests/unpack-selftests.c,
unittests/utils-selftests.c, unittests/xml-utils-selftests.c,
utils.c, utils.h, valarith.c, valops.c, valprint.c, value.c,
value.h, varobj.c, varobj.h, windows-nat.c, x86-linux-nat.c,
xml-support.c, xml-support.h, xml-tdesc.h, xstormy16-tdep.c,
xtensa-linux-nat.c, dwarf2read.h: Change common to gdbsupport.
gdb/gdbserver/ChangeLog
2019-07-09 Tom Tromey <tom@tromey.com>
* configure: Rebuild.
* configure.ac: Change common to gdbsupport.
* acinclude.m4: Change common to gdbsupport.
* Makefile.in (SFILES, OBS, GDBREPLAY_OBS, IPA_OBJS)
(version-generated.c, gdbsupport/%-ipa.o, gdbsupport/%.o): Change
common to gdbsupport.
* ax.c, event-loop.c, fork-child.c, gdb_proc_service.h,
gdbreplay.c, gdbthread.h, hostio-errno.c, hostio.c, i387-fp.c,
inferiors.c, inferiors.h, linux-aarch64-tdesc-selftest.c,
linux-amd64-ipa.c, linux-i386-ipa.c, linux-low.c,
linux-tic6x-low.c, linux-x86-low.c, linux-x86-tdesc-selftest.c,
linux-x86-tdesc.c, lynx-i386-low.c, lynx-low.c, mem-break.h,
nto-x86-low.c, regcache.c, regcache.h, remote-utils.c, server.c,
server.h, spu-low.c, symbol.c, target.h, tdesc.c, tdesc.h,
thread-db.c, tracepoint.c, win32-i386-low.c, win32-low.c: Change
common to gdbsupport.
2019-05-06 10:29:24 +08:00
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#include "gdbsupport/def-vector.h"
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Introduce gdb::byte_vector, add allocator that default-initializes
In some cases we've been replacing heap-allocated gdb_byte buffers
managed with xmalloc/make_cleanup(xfree) with gdb::vector<gdb_byte>.
That usually pessimizes the code a little bit because std::vector
value-initializes elements (which for gdb_byte means
zero-initialization), while if you're creating a temporary buffer,
you're most certaintly going to fill it in with some data. An
alternative is to use
unique_ptr<gdb_byte[]> buf (new gdb_byte[size]);
but it looks like that's not very popular.
Recently, a use of obstacks in dwarf2read.c was replaced with
std::vector<gdb_byte> and that as well introduced a pessimization for
always memsetting the buffer when it's garanteed that the zeros will
be overwritten immediately. (see dwarf2read.c change in this patch to
find it.)
So here's a different take at addressing this issue "by design":
#1 - Introduce default_init_allocator<T>
I.e., a custom allocator that does default construction using default
initialization, meaning, no more zero initialization. That's the
default_init_allocation<T> class added in this patch.
See "Notes" at
<http://en.cppreference.com/w/cpp/container/vector/resize>.
#2 - Introduce def_vector<T>
I.e., a convenience typedef, because typing the allocator is annoying:
using def_vector<T> = std::vector<T, gdb::default_init_allocator<T>>;
#3 - Introduce byte_vector
Because gdb_byte vectors will be the common thing, add a convenience
"byte_vector" typedef:
using byte_vector = def_vector<gdb_byte>;
which is really the same as:
std::vector<gdb_byte, gdb::default_init_allocator<gdb_byte>>;
The intent then is to make "gdb::byte_vector" be the go-to for dynamic
byte buffers. So the less friction, the better.
#4 - Adjust current code to use it.
To set the example going forward. Replace std::vector uses and also
unique_ptr<byte[]> uses.
One nice thing is that with this allocator, for changes like these:
-std::unique_ptr<byte[]> buf (new gdb_byte[some_size]);
+gdb::byte_vector buf (some_size);
fill_with_data (buf.data (), buf.size ());
the generated code is the same as before. I.e., the compiler
de-structures the vector and gets rid of the unused "reserved vs size"
related fields.
The other nice thing is that it's easier to write
gdb::byte_vector buf (size);
than
std::unique_ptr<gdb_byte[]> buf (new gdb_byte[size]);
or even (C++14):
auto buf = std::make_unique<gdb_byte[]> (size); // zero-initializes...
#5 - Suggest s/std::vector<gdb_byte>/gdb::byte_vector/ going forward.
Note that this commit actually fixes a couple of bugs where the current
code is incorrectly using "std::vector::reserve(new_size)" and then
accessing the vector's internal buffer beyond the vector's size: see
dwarf2loc.c and charset.c. That's undefined behavior and may trigger
debug mode assertion failures. With default_init_allocator,
"resize()" behaves like "reserve()" performance wise, in that it
leaves new elements with unspecified values, but, it does that safely
without triggering undefined behavior when you access those values.
gdb/ChangeLog:
2017-06-14 Pedro Alves <palves@redhat.com>
* ada-lang.c: Include "common/byte-vector.h".
(ada_value_primitive_packed_val): Use gdb::byte_vector.
* charset.c (wchar_iterator::iterate): Resize the vector instead
of reserving it.
* common/byte-vector.h: Include "common/def-vector.h".
(wchar_iterator::m_out): Now a gdb::def_vector<gdb_wchar_t>.
* cli/cli-dump.c: Include "common/byte-vector.h".
(dump_memory_to_file, restore_binary_file): Use gdb::byte_vector.
* common/byte-vector.h: New file.
* common/def-vector.h: New file.
* common/default-init-alloc.h: New file.
* dwarf2loc.c: Include "common/byte-vector.h".
(rw_pieced_value): Use gdb::byte_vector, and resize the vector
instead of reserving it.
* dwarf2read.c: Include "common/byte-vector.h".
(data_buf::m_vec): Now a gdb::byte_vector.
* gdb_regex.c: Include "common/def-vector.h".
(compiled_regex::compiled_regex): Use gdb::def_vector<char>.
* mi/mi-main.c: Include "common/byte-vector.h".
(mi_cmd_data_read_memory): Use gdb::byte_vector.
* printcmd.c: Include "common/byte-vector.h".
(print_scalar_formatted): Use gdb::byte_vector.
* valprint.c: Include "common/byte-vector.h".
(maybe_negate_by_bytes, print_decimal_chars): Use
gdb::byte_vector.
2017-06-14 18:08:52 +08:00
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namespace gdb {
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/* byte_vector is a gdb_byte std::vector with a custom allocator that
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unlike std::vector<gdb_byte> does not zero-initialize new elements
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by default when the vector is created/resized. This is what you
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usually want when working with byte buffers, since if you're
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creating or growing a buffer you'll most surely want to fill it in
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with data, in which case zero-initialization would be a
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pessimization. For example:
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gdb::byte_vector buf (some_large_size);
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fill_with_data (buf.data (), buf.size ());
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On the odd case you do need zero initialization, then you can still
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call the overloads that specify an explicit value, like:
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gdb::byte_vector buf (some_initial_size, 0);
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buf.resize (a_bigger_size, 0);
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(Or use std::vector<gdb_byte> instead.)
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Note that unlike std::vector<gdb_byte>, function local
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gdb::byte_vector objects constructed with an initial size like:
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gdb::byte_vector buf (some_size);
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fill_with_data (buf.data (), buf.size ());
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usually compile down to the exact same as:
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std::unique_ptr<byte[]> buf (new gdb_byte[some_size]);
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fill_with_data (buf.get (), some_size);
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with the former having the advantage of being a bit more readable,
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and providing the whole std::vector API, if you end up needing it.
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*/
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using byte_vector = gdb::def_vector<gdb_byte>;
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Make target_read_alloc & al return vectors
This patch started by changing target_read_alloc_1 to return a
byte_vector, to avoid manual memory management (in target_read_alloc_1
and in the callers). To communicate failures to the callers, it
actually returns a gdb::optional<gdb::byte_vector>.
Adjusting target_read_stralloc was a bit more tricky, since it wants to
return a buffer of char, and not gdb_byte. Since you can't just cast a
gdb::byte_vector into a gdb::def_vector<char>, I made
target_read_alloc_1 templated, so both versions (that return vectors of
gdb_byte and char) are generated. Since target_read_stralloc now
returns a gdb::char_vector instead of a gdb::unique_xmalloc_ptr<char>, a
few callers need to be adjusted.
gdb/ChangeLog:
* common/byte-vector.h (char_vector): New type.
* target.h (target_read_alloc): Return
gdb::optional<byte_vector>.
(target_read_stralloc): Return gdb::optional<char_vector>.
(target_get_osdata): Return gdb::optional<char_vector>.
* target.c (target_read_alloc_1): Templatize. Replacement
manual memory management with vector.
(target_read_alloc): Change return type, adjust.
(target_read_stralloc): Change return type, adjust.
(target_get_osdata): Change return type, adjust.
* auxv.c (struct auxv_info) <length>: Remove.
<data>: Change type to gdb::optional<byte_vector>.
(auxv_inferior_data_cleanup): Free auxv_info with delete.
(get_auxv_inferior_data): Allocate auxv_info with new, adjust.
(target_auxv_search): Adjust.
(fprint_target_auxv): Adjust.
* avr-tdep.c (avr_io_reg_read_command): Adjust.
* linux-tdep.c (linux_spu_make_corefile_notes): Adjust.
(linux_make_corefile_notes): Adjust.
* osdata.c (get_osdata): Adjust.
* remote.c (remote_get_threads_with_qxfer): Adjust.
(remote_memory_map): Adjust.
(remote_traceframe_info): Adjust.
(btrace_read_config): Adjust.
(remote_read_btrace): Adjust.
(remote_pid_to_exec_file): Adjust.
* solib-aix.c (solib_aix_get_library_list): Adjust.
* solib-dsbt.c (decode_loadmap): Don't free buf.
(dsbt_get_initial_loadmaps): Adjust.
* solib-svr4.c (svr4_current_sos_via_xfer_libraries): Adjust.
* solib-target.c (solib_target_current_sos): Adjust.
* tracepoint.c (sdata_make_value): Adjust.
* xml-support.c (xinclude_start_include): Adjust.
(xml_fetch_content_from_file): Adjust.
* xml-support.h (xml_fetch_another): Change return type.
(xml_fetch_content_from_file): Change return type.
* xml-syscall.c (xml_init_syscalls_info): Adjust.
* xml-tdesc.c (file_read_description_xml): Adjust.
(fetch_available_features_from_target): Change return type.
(target_fetch_description_xml): Adjust.
(target_read_description_xml): Adjust.
2018-04-08 01:19:12 +08:00
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using char_vector = gdb::def_vector<char>;
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Introduce gdb::byte_vector, add allocator that default-initializes
In some cases we've been replacing heap-allocated gdb_byte buffers
managed with xmalloc/make_cleanup(xfree) with gdb::vector<gdb_byte>.
That usually pessimizes the code a little bit because std::vector
value-initializes elements (which for gdb_byte means
zero-initialization), while if you're creating a temporary buffer,
you're most certaintly going to fill it in with some data. An
alternative is to use
unique_ptr<gdb_byte[]> buf (new gdb_byte[size]);
but it looks like that's not very popular.
Recently, a use of obstacks in dwarf2read.c was replaced with
std::vector<gdb_byte> and that as well introduced a pessimization for
always memsetting the buffer when it's garanteed that the zeros will
be overwritten immediately. (see dwarf2read.c change in this patch to
find it.)
So here's a different take at addressing this issue "by design":
#1 - Introduce default_init_allocator<T>
I.e., a custom allocator that does default construction using default
initialization, meaning, no more zero initialization. That's the
default_init_allocation<T> class added in this patch.
See "Notes" at
<http://en.cppreference.com/w/cpp/container/vector/resize>.
#2 - Introduce def_vector<T>
I.e., a convenience typedef, because typing the allocator is annoying:
using def_vector<T> = std::vector<T, gdb::default_init_allocator<T>>;
#3 - Introduce byte_vector
Because gdb_byte vectors will be the common thing, add a convenience
"byte_vector" typedef:
using byte_vector = def_vector<gdb_byte>;
which is really the same as:
std::vector<gdb_byte, gdb::default_init_allocator<gdb_byte>>;
The intent then is to make "gdb::byte_vector" be the go-to for dynamic
byte buffers. So the less friction, the better.
#4 - Adjust current code to use it.
To set the example going forward. Replace std::vector uses and also
unique_ptr<byte[]> uses.
One nice thing is that with this allocator, for changes like these:
-std::unique_ptr<byte[]> buf (new gdb_byte[some_size]);
+gdb::byte_vector buf (some_size);
fill_with_data (buf.data (), buf.size ());
the generated code is the same as before. I.e., the compiler
de-structures the vector and gets rid of the unused "reserved vs size"
related fields.
The other nice thing is that it's easier to write
gdb::byte_vector buf (size);
than
std::unique_ptr<gdb_byte[]> buf (new gdb_byte[size]);
or even (C++14):
auto buf = std::make_unique<gdb_byte[]> (size); // zero-initializes...
#5 - Suggest s/std::vector<gdb_byte>/gdb::byte_vector/ going forward.
Note that this commit actually fixes a couple of bugs where the current
code is incorrectly using "std::vector::reserve(new_size)" and then
accessing the vector's internal buffer beyond the vector's size: see
dwarf2loc.c and charset.c. That's undefined behavior and may trigger
debug mode assertion failures. With default_init_allocator,
"resize()" behaves like "reserve()" performance wise, in that it
leaves new elements with unspecified values, but, it does that safely
without triggering undefined behavior when you access those values.
gdb/ChangeLog:
2017-06-14 Pedro Alves <palves@redhat.com>
* ada-lang.c: Include "common/byte-vector.h".
(ada_value_primitive_packed_val): Use gdb::byte_vector.
* charset.c (wchar_iterator::iterate): Resize the vector instead
of reserving it.
* common/byte-vector.h: Include "common/def-vector.h".
(wchar_iterator::m_out): Now a gdb::def_vector<gdb_wchar_t>.
* cli/cli-dump.c: Include "common/byte-vector.h".
(dump_memory_to_file, restore_binary_file): Use gdb::byte_vector.
* common/byte-vector.h: New file.
* common/def-vector.h: New file.
* common/default-init-alloc.h: New file.
* dwarf2loc.c: Include "common/byte-vector.h".
(rw_pieced_value): Use gdb::byte_vector, and resize the vector
instead of reserving it.
* dwarf2read.c: Include "common/byte-vector.h".
(data_buf::m_vec): Now a gdb::byte_vector.
* gdb_regex.c: Include "common/def-vector.h".
(compiled_regex::compiled_regex): Use gdb::def_vector<char>.
* mi/mi-main.c: Include "common/byte-vector.h".
(mi_cmd_data_read_memory): Use gdb::byte_vector.
* printcmd.c: Include "common/byte-vector.h".
(print_scalar_formatted): Use gdb::byte_vector.
* valprint.c: Include "common/byte-vector.h".
(maybe_negate_by_bytes, print_decimal_chars): Use
gdb::byte_vector.
2017-06-14 18:08:52 +08:00
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} /* namespace gdb */
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#endif /* COMMON_DEF_VECTOR_H */
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