aboutsummaryrefslogtreecommitdiff
path: root/gdb/mi
diff options
context:
space:
mode:
authorPedro Alves <palves@redhat.com>2017-06-14 11:08:52 +0100
committerPedro Alves <palves@redhat.com>2017-06-14 11:08:52 +0100
commitd5722aa2fe9e1d76d98865a9ab77a7b9388743c9 (patch)
treeeab6915dacaedb1b9189c6d6bd6a3df02aa2ceec /gdb/mi
parent05c966f3c98d6126404f1cd7f233148a89810b5d (diff)
downloadgdb-d5722aa2fe9e1d76d98865a9ab77a7b9388743c9.zip
gdb-d5722aa2fe9e1d76d98865a9ab77a7b9388743c9.tar.gz
gdb-d5722aa2fe9e1d76d98865a9ab77a7b9388743c9.tar.bz2
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.
Diffstat (limited to 'gdb/mi')
-rw-r--r--gdb/mi/mi-main.c5
1 files changed, 3 insertions, 2 deletions
diff --git a/gdb/mi/mi-main.c b/gdb/mi/mi-main.c
index 755fbab..53289bb 100644
--- a/gdb/mi/mi-main.c
+++ b/gdb/mi/mi-main.c
@@ -55,6 +55,7 @@
#include "gdbcmd.h"
#include "observer.h"
#include "common/gdb_optional.h"
+#include "common/byte-vector.h"
#include <ctype.h>
#include "run-time-clock.h"
@@ -1466,12 +1467,12 @@ mi_cmd_data_read_memory (const char *command, char **argv, int argc)
/* Create a buffer and read it in. */
total_bytes = word_size * nr_rows * nr_cols;
- std::unique_ptr<gdb_byte[]> mbuf (new gdb_byte[total_bytes]);
+ gdb::byte_vector mbuf (total_bytes);
/* Dispatch memory reads to the topmost target, not the flattened
current_target. */
nr_bytes = target_read (current_target.beneath,
- TARGET_OBJECT_MEMORY, NULL, mbuf.get (),
+ TARGET_OBJECT_MEMORY, NULL, mbuf.data (),
addr, total_bytes);
if (nr_bytes <= 0)
error (_("Unable to read memory."));