What has changed in GDB?
(Organized release by release)
-*** Changes since GDB 7.1
+*** Changes since GDB 7.2
+
+* Python scripting
+
+ ** GDB values in Python are now callable if the value represents a
+ function. For example, if 'some_value' represents a function that
+ takes two integer parameters and returns a value, you can call
+ that function like so:
+
+ result = some_value (10,20)
+
+* C++ Improvements:
+
+ ** GDB now puts template parameters in scope when debugging in an
+ instantiation. For example, if you have:
+
+ template<int X> int func (void) { return X; }
+
+ then if you step into func<5>, "print X" will show "5". This
+ feature requires proper debuginfo support from the compiler; it
+ was added to GCC 4.5.
+
+* GDB now has some support for using labels in the program's source in
+ linespecs. For instance, you can use "advance label" to continue
+ execution to a label.
+
+* GDB now has support for reading and writing a new .gdb_index
+ section. This section holds a fast index of DWARF debugging
+ information and can be used to greatly speed up GDB startup and
+ operation. See the documentation for `save gdb-index' for details.
+
+* The "watch" command now accepts an optional "-location" argument.
+ When used, this causes GDB to watch the memory referred to by the
+ expression. Such a watchpoint is never deleted due to it going out
+ of scope.
+
+* GDB now supports thread debugging of core dumps on GNU/Linux.
+
+ GDB now activates thread debugging using the libthread_db library
+ when debugging GNU/Linux core dumps, similarly to when debugging
+ live processes. As a result, when debugging a core dump file, GDB
+ is now able to display pthread_t ids of threads. For example, "info
+ threads" shows the same output as when debugging the process when it
+ was live. In earlier releases, you'd see something like this:
+
+ (gdb) info threads
+ * 1 LWP 6780 main () at main.c:10
+
+ While now you see this:
+
+ (gdb) info threads
+ * 1 Thread 0x7f0f5712a700 (LWP 6780) main () at main.c:10
+
+ It is also now possible to inspect TLS variables when debugging core
+ dumps.
+
+ When debugging a core dump generated on a machine other than the one
+ used to run GDB, you may need to point GDB at the correct
+ libthread_db library with the "set libthread-db-search-path"
+ command. See the user manual for more details on this command.
+
+* New features in the GDB remote stub, GDBserver
+
+ ** GDBserver is now supported on PowerPC LynxOS 4.x.
+
+*** Changes in GDB 7.2
+
+* Shared library support for remote targets by default
+
+ When GDB is configured for a generic, non-OS specific target, like
+ for example, --target=arm-eabi or one of the many *-*-elf targets,
+ GDB now queries remote stubs for loaded shared libraries using the
+ `qXfer:libraries:read' packet. Previously, shared library support
+ was always disabled for such configurations.
* C++ Improvements:
GDB now also supports proper overload resolution for all the previously
mentioned flavors of operators.
+ ** static const class members
+
+ Printing of static const class members that are initialized in the
+ class definition has been fixed.
+
* Windows Thread Information Block access.
On Windows targets, GDB now supports displaying the Windows Thread
thread-specific pointer to the TIB. This feature is also supported
when remote debugging using GDBserver.
+* Static tracepoints
+
+ Static tracepoints are calls in the user program into a tracing
+ library. One such library is a port of the LTTng kernel tracer to
+ userspace --- UST (LTTng Userspace Tracer, http://lttng.org/ust).
+ When debugging with GDBserver, GDB now supports combining the GDB
+ tracepoint machinery with such libraries. For example: the user can
+ use GDB to probe a static tracepoint marker (a call from the user
+ program into the tracing library) with the new "strace" command (see
+ "New commands" below). This creates a "static tracepoint" in the
+ breakpoint list, that can be manipulated with the same feature set
+ as fast and regular tracepoints. E.g., collect registers, local and
+ global variables, collect trace state variables, and define
+ tracepoint conditions. In addition, the user can collect extra
+ static tracepoint marker specific data, by collecting the new
+ $_sdata internal variable. When analyzing the trace buffer, you can
+ inspect $_sdata like any other variable available to GDB. For more
+ information, see the "Tracepoints" chapter in GDB user manual. New
+ remote packets have been defined to support static tracepoints, see
+ the "New remote packets" section below.
+
+* Better reconstruction of tracepoints after disconnected tracing
+
+ GDB will attempt to download the original source form of tracepoint
+ definitions when starting a trace run, and then will upload these
+ upon reconnection to the target, resulting in a more accurate
+ reconstruction of the tracepoints that are in use on the target.
+
+* Observer mode
+
+ You can now exercise direct control over the ways that GDB can
+ affect your program. For instance, you can disallow the setting of
+ breakpoints, so that the program can run continuously (assuming
+ non-stop mode). In addition, the "observer" variable is available
+ to switch all of the different controls; in observer mode, GDB
+ cannot affect the target's behavior at all, which is useful for
+ tasks like diagnosing live systems in the field.
+
+* The new convenience variable $_thread holds the number of the
+ current thread.
+
* New remote packets
qGetTIBAddr
is particularly useful for stubs that support fast tracepoints. GDB
reports support for this feature in the qSupported packet.
+qTfSTM, qTsSTM
+
+ List static tracepoint markers in the target program.
+
+qTSTMat
+
+ List static tracepoint markers at a given address in the target
+ program.
+
+qXfer:statictrace:read
+
+ Read the static trace data collected (by a `collect $_sdata'
+ tracepoint action). The remote stub reports support for this packet
+ to gdb's qSupported query.
+
+QAllow
+
+ Send the current settings of GDB's permission flags.
+
+QTDPsrc
+
+ Send part of the source (textual) form of a tracepoint definition,
+ which includes location, conditional, and action list.
+
* The source command now accepts a -s option to force searching for the
script in the source search path even if the script name specifies
a directory.
* New features in the GDB remote stub, GDBserver
- - GDBserver now support tracepoints (including fast tracepoints).
- The feature is currently supported by the i386-linux and
- amd64-linux builds. See the "Tracepoints support in gdbserver"
- section in the manual for more information. GDBserver JIT
- compiles the tracepoint's conditional agent expression bytecode
- into native code whenever possible for low overhead dynamic
- tracepoints conditionals. For such tracepoints, an expression
- that examines program state is evaluated when the tracepoint is
- reached, in order to determine whether to capture trace data. If
- the condition is simple and false, processing the tracepoint
- finishes very quickly and no data is gathered.
+ - GDBserver now support tracepoints (including fast tracepoints, and
+ static tracepoints). The feature is currently supported by the
+ i386-linux and amd64-linux builds. See the "Tracepoints support
+ in gdbserver" section in the manual for more information.
+
+ GDBserver JIT compiles the tracepoint's conditional agent
+ expression bytecode into native code whenever possible for low
+ overhead dynamic tracepoints conditionals. For such tracepoints,
+ an expression that examines program state is evaluated when the
+ tracepoint is reached, in order to determine whether to capture
+ trace data. If the condition is simple and false, processing the
+ tracepoint finishes very quickly and no data is gathered.
+
+ GDBserver interfaces with the UST (LTTng Userspace Tracer) library
+ for static tracepoints support.
- GDBserver now supports x86_64 Windows 64-bit debugging.
`save tracepoints' is a new alias for `save-tracepoints'. The latter
is now deprecated.
+info static-tracepoint-markers
+ Display information about static tracepoint markers in the target.
+
+strace FN | FILE:LINE | *ADDR | -m MARKER_ID
+ Define a static tracepoint by probing a marker at the given
+ function, line, address, or marker ID.
+
+set observer on|off
+show observer
+ Enable and disable observer mode.
+
+set may-write-registers on|off
+set may-write-memory on|off
+set may-insert-breakpoints on|off
+set may-insert-tracepoints on|off
+set may-insert-fast-tracepoints on|off
+set may-interrupt on|off
+ Set individual permissions for GDB effects on the target. Note that
+ some of these settings can have undesirable or surprising
+ consequences, particularly when changed in the middle of a session.
+ For instance, disabling the writing of memory can prevent
+ breakpoints from being inserted, cause single-stepping to fail, or
+ even crash your program, if you disable after breakpoints have been
+ inserted. However, GDB should not crash.
+
+set record memory-query on|off
+show record memory-query
+ Control whether to stop the inferior if memory changes caused
+ by an instruction cannot be recorded.
+
+* Changed commands
+
+disassemble
+ The disassemble command now supports "start,+length" form of two arguments.
+
* Python scripting
** GDB now provides a new directory location, called the python directory,
GDB now supports debugging programs written in the D programming
language.
+* GDB now supports the extended ptrace interface for PowerPC which is
+ available since Linux kernel version 2.6.34. This automatically enables
+ any hardware breakpoints and additional hardware watchpoints available in
+ the processor. The old ptrace interface exposes just one hardware
+ watchpoint and no hardware breakpoints.
+
+* GDB is now able to use the Data Value Compare (DVC) register available on
+ embedded PowerPC processors to implement in hardware simple watchpoint
+ conditions of the form:
+
+ watch ADDRESS|VARIABLE if ADDRESS|VARIABLE == CONSTANT EXPRESSION
+
+ This works in native GDB running on Linux kernels with the extended ptrace
+ interface mentioned above.
+
*** Changes in GDB 7.1
* C++ Improvements
the target for evaluation using the same bytecode format as is used
for tracepoint actions.
-* "disassemble" command with a /r modifier, print the raw instructions
-in hex as well as in symbolic form.
+* The disassemble command now supports: an optional /r modifier, print the
+raw instructions in hex as well as in symbolic form, and an optional /m
+modifier to print mixed source+assembly.
* Process record and replay
packet that permited the stub to pass a process id was removed.
Remote servers should use the `T' stop reply packet instead.
-* The "disassemble" command now supports an optional /m modifier to print mixed
-source+assembly.
-
* GDB now supports multiple function calling conventions according to the
DWARF-2 DW_AT_calling_convention function attribute.