Hi Guys,
First of all I have an apology to make. I managed to reformat my
hard drive over the holidays, wiping away all of my notes for this
blog. In particular I was contacted by a reader about an
enhancement to gcc's inline assembler support which I have now
totally lost. :-( So, dear reader, wherever you are, I apologise,
and if you contact me again I will make sure that the extended asm
enhancement gets mentioned in the next blog post.
The big news, for me at least, is that binutils 2.26 is now out.
This release contains lots of bug fixes of course, plus a few new
features:
* A new configure option:
--enable-compressed-debug-sections={all,gas,gold,ld,none}
which decides whether DWARF debug sections should be compressed
by default. By default this option is off for all of the tools,
although of course it can be enabled via command line options.
In future releases of binutils however, the option will be
enabled by default.
* Support for the ARC EM/HS and ARC600/700 architectures.
* Support for the LLVM plugin.
* Experimental support for linker garbage collection (--gc-sections)
for COFF and PE based targets.
* A new linker command line option:
--orphan-handling=[place|warn|error|discard]
is available which adjusts how orphan sections are handled. The
default is 'place' which gives the normal behaviour. 'warn' and
'error' issue a warning or error respectively when an orphan
section is found, and 'discard' will discard the section entirely.
* The objcopy tool has a new option insert symbols into a file:
--add-symbol <name>=[<section>:]<value>[,<flags>]
It also has a new option to replace the contents of an existing
section with the contents of a specified file:
--update-section <section>=<filename>
* In the assembler, symbol and label names can now be enclosed in
double quotes (") which allows them to contain characters that
are not part of valid symbol names in high level languages.
* Support for the ARMv8.1 architecture has been added to the
AArch64 and ARM ports.
The next binutils release (2.27) should be happening in July of
this year as the project attempts to move to a 6 month release
schedule.
In the development binutils there is now support for ARM NOREAD
sections. These are executable sections which contain code which
the user is not allowed to see.
Next - there is a new release of the Newlib C library. Version
2.3.0 contains several enhancements and improvements, including:
- Dynamic atexit logic fixed.
- ARM performance enhancements.
- New version of strtold.
- ARC platform support redone.
- Strftime improvements/enhancements.
- Complex math enhancements.
- Visium platform support added.
- OR1K platform support added.
GCC meanwhile continues working on reducing bug numbers so that a
version 6 branch can be created. In practice this means that new
features are not being added to the sources at this point, although
there is one new warning option to report:
-Winvalid-memory-model
This warns for invocations of__atomic Builtins, __sync Builtins, and
the C11 atomic generic functions with a memory consistency argument
that is either invalid for the operation or outside the range of
values of the memory_order enumeration. For example, since the
__atomic_store and __atomic_store_n built-ins are only defined for
the relaxed, release, and sequentially consistent memory orders the
following code will produce a warning:
void store (int *i)
{
__atomic_store_n (i, 0, memory_order_consume);
}
This option is enabled by default.
The development version of GCC also no longer supports DWARF Version
1, which is substantially different than Version 2 and later. For
historical reasons, some other DWARF-related options (including
-feliminate-dwarf2-dups and -fno-dwarf2-cfi-asm) retain a reference
to DWARF Version 2 in their names, but apply to all
currently-supported versions of DWARF.
The GDB debugger continues to improve as well, and in the last
couple of months these new features have been added to the
development version:
* Support for debugging kernel-based threads on FreeBSD.
* Thread numbers are now per inferior instead of global. If
you are debugging multiple inferiors, GDB displays thread IDs
using a qualified INF_NUM.THR_NUM form. For example:
(gdb) info threads
Id Target Id Frame
1.1 Thread 0x7ffff7fc2740 (LWP 8155) (running)
1.2 Thread 0x7ffff7fc1700 (LWP 8168) (running)
* 2.1 Thread 0x7ffff7fc2740 (LWP 8157) (running)
2.2 Thread 0x7ffff7fc1700 (LWP 8190) (running)
As consequence, thread numbers as visible in the $_thread
convenience variable and in Python's InferiorThread.num attribute
are no longer unique between inferiors.
GDB now maintains a second thread ID per thread, referred to as
the global thread ID, which is the new equivalent of thread
numbers in previous releases. See also $_gthread below.
For backwards compatibility, MI's thread IDs always refer to
global IDs.
Commands that accept thread IDs now accept the qualified
INF_NUM.THR_NUM form as well. For example:
(gdb) thread 2.1
[Switching to thread 2.1 (Thread 0x7ffff7fc2740 (LWP 8157))] (running)
(gdb)
In commands that accept a list of thread IDs, you can now refer
to all threads of an inferior using a star wildcard. GDB accepts
"INF_NUM.*", to refer to all threads of inferior INF_NUM, and "*"
to refer to all threads of the current inferior. For example,
"info threads 2.*".
You can use "info threads -gid" to display the global thread ID
of all threads.
The new convenience variable $_gthread holds the global number of
the current thread, and $_inferior holds the number of the
current inferior.
* GDB now displays the ID and name of the thread that hit a breakpoint
or received a signal, if your program is multi-threaded. For
example:
Thread 3 "bar" hit Breakpoint 1 at 0x40087a: file program.c, line 20.
Thread 1 "main" received signal SIGINT, Interrupt.
That's all for now. More again in a couple of month's time.
Cheers
Nick
