Pedro Alves 503b1c39dc gdb: Replace operator new / operator new[]
If xmalloc fails allocating memory, usually because something tried a
huge allocation, like xmalloc(-1) or some such, GDB asks the user what
to do:

  .../src/gdb/utils.c:1079: internal-error: virtual memory exhausted.
  A problem internal to GDB has been detected,
  further debugging may prove unreliable.
  Quit this debugging session? (y or n)

If the user says "n", that throws a QUIT exception, which is caught by
one of the multiple CATCH(RETURN_MASK_ALL) blocks somewhere up the
stack.

The default implementations of operator new / operator new[] call
malloc directly, and on memory allocation failure throw
std::bad_alloc.  Currently, if that happens, since nothing catches it,
the exception escapes out of main, and GDB aborts from unhandled
exception.

This patch replaces the default operator new variants with versions
that, just like xmalloc:

 #1 - Raise an internal-error on memory allocation failure.

 #2 - Throw a QUIT gdb_exception, so that the exact same CATCH blocks
      continue handling memory allocation problems.

A minor complication of #2 is that operator new can _only_ throw
std::bad_alloc, or something that extends it:

  void* operator new (std::size_t size) throw (std::bad_alloc);

That means that if we let a gdb QUIT exception escape from within
operator new, the C++ runtime aborts due to unexpected exception
thrown.

So to bridge the gap, this patch adds a new gdb_quit_bad_alloc
exception type that inherits both std::bad_alloc and gdb_exception,
and throws _that_.

If we decide that we should be catching memory allocation errors in
fewer places than all the places we currently catch them (everywhere
we use RETURN_MASK_ALL currently), then we could change operator new
to throw plain std::bad_alloc then.  But I'm considering such a change
as separate matter from this one -- it'd make sense to do the same to
xmalloc at the same time, for instance.

Meanwhile, this allows using new/new[] instead of xmalloc/XNEW/etc.
without losing the "virtual memory exhausted" internal-error
safeguard.

Tested on x86_64 Fedora 23.

gdb/ChangeLog:
2016-09-23  Pedro Alves  <palves@redhat.com>

	* Makefile.in (SFILES): Add common/new-op.c.
	(COMMON_OBS): Add common/new-op.o.
	(new-op.o): New rule.
	* common/common-exceptions.h: Include <new>.
	(struct gdb_quit_bad_alloc): New type.
	* common/new-op.c: New file.

gdb/gdbserver/ChangeLog:
2016-09-23  Pedro Alves  <palves@redhat.com>

	* Makefile.in (SFILES): Add common/new-op.c.
	(OBS): Add common/new-op.o.
	(new-op.o): New rule.
2016-09-23 16:42:24 +01:00
..
2016-09-21 13:12:21 -04:00
2016-09-05 19:10:44 +01:00
2016-01-12 10:34:17 -05:00
2016-09-05 19:10:44 +01:00
2016-09-05 19:10:44 +01:00
2016-07-21 12:12:18 +01:00
2016-05-04 19:42:09 -04:00
2016-04-12 17:17:13 +01:00
2016-06-03 11:29:25 +00:00

		   README for GDBserver & GDBreplay
		    by Stu Grossman and Fred Fish

Introduction:

This is GDBserver, a remote server for Un*x-like systems.  It can be used to
control the execution of a program on a target system from a GDB on a different
host.  GDB and GDBserver communicate using the standard remote serial protocol
implemented in remote.c, and various *-stub.c files.  They communicate via
either a serial line or a TCP connection.

For more information about GDBserver, see the GDB manual.

Usage (server (target) side):

First, you need to have a copy of the program you want to debug put onto
the target system.  The program can be stripped to save space if needed, as
GDBserver doesn't care about symbols.  All symbol handling is taken care of by
the GDB running on the host system.

To use the server, you log on to the target system, and run the `gdbserver'
program.  You must tell it (a) how to communicate with GDB, (b) the name of
your program, and (c) its arguments.  The general syntax is:

	target> gdbserver COMM PROGRAM [ARGS ...]

For example, using a serial port, you might say:

	target> gdbserver /dev/com1 emacs foo.txt

This tells GDBserver to debug emacs with an argument of foo.txt, and to
communicate with GDB via /dev/com1.  GDBserver now waits patiently for the
host GDB to communicate with it.

To use a TCP connection, you could say:

	target> gdbserver host:2345 emacs foo.txt

This says pretty much the same thing as the last example, except that we are
going to communicate with the host GDB via TCP.  The `host:2345' argument means
that we are expecting to see a TCP connection from `host' to local TCP port
2345.  (Currently, the `host' part is ignored.)  You can choose any number you
want for the port number as long as it does not conflict with any existing TCP
ports on the target system.  This same port number must be used in the host
GDBs `target remote' command, which will be described shortly.  Note that if
you chose a port number that conflicts with another service, GDBserver will
print an error message and exit.

On some targets, GDBserver can also attach to running programs.  This is
accomplished via the --attach argument.  The syntax is:

	target> gdbserver --attach COMM PID

PID is the process ID of a currently running process.  It isn't necessary
to point GDBserver at a binary for the running process.

Usage (host side):

You need an unstripped copy of the target program on your host system, since
GDB needs to examine it's symbol tables and such.  Start up GDB as you normally
would, with the target program as the first argument.  (You may need to use the
--baud option if the serial line is running at anything except 9600 baud.)
Ie: `gdb TARGET-PROG', or `gdb --baud BAUD TARGET-PROG'.  After that, the only
new command you need to know about is `target remote'.  It's argument is either
a device name (usually a serial device, like `/dev/ttyb'), or a HOST:PORT
descriptor.  For example:

	(gdb) target remote /dev/ttyb

communicates with the server via serial line /dev/ttyb, and:

	(gdb) target remote the-target:2345

communicates via a TCP connection to port 2345 on host `the-target', where
you previously started up GDBserver with the same port number.  Note that for
TCP connections, you must start up GDBserver prior to using the `target remote'
command, otherwise you may get an error that looks something like
`Connection refused'.

Building GDBserver:

The supported targets as of November 2006 are:
	arm-*-linux*
	bfin-*-uclinux
	bfin-*-linux-uclibc
	crisv32-*-linux*
	cris-*-linux*
	i[34567]86-*-cygwin*
	i[34567]86-*-linux*
	i[34567]86-*-mingw*
	ia64-*-linux*
	m32r*-*-linux*
	m68*-*-linux*
	m68*-*-uclinux*
	mips*64*-*-linux*
	mips*-*-linux*
	powerpc[64]-*-linux*
	s390[x]-*-linux*
	sh-*-linux*
	spu*-*-*
	x86_64-*-linux*

Configuring GDBserver you should specify the same machine for host and
target (which are the machine that GDBserver is going to run on.  This
is not the same as the machine that GDB is going to run on; building
GDBserver automatically as part of building a whole tree of tools does
not currently work if cross-compilation is involved (we don't get the
right CC in the Makefile, to start with)).

Building GDBserver for your target is very straightforward.  If you build
GDB natively on a target which GDBserver supports, it will be built
automatically when you build GDB.  You can also build just GDBserver:

	% mkdir obj
	% cd obj
	% path-to-gdbserver-sources/configure
	% make

If you prefer to cross-compile to your target, then you can also build
GDBserver that way.  In a Bourne shell, for example:

	% export CC=your-cross-compiler
	% path-to-gdbserver-sources/configure your-target-name
	% make

Using GDBreplay:

A special hacked down version of GDBserver can be used to replay remote
debug log files created by GDB.  Before using the GDB "target" command to
initiate a remote debug session, use "set remotelogfile <filename>" to tell
GDB that you want to make a recording of the serial or tcp session.  Note
that when replaying the session, GDB communicates with GDBreplay via tcp,
regardless of whether the original session was via a serial link or tcp.

Once you are done with the remote debug session, start GDBreplay and
tell it the name of the log file and the host and port number that GDB
should connect to (typically the same as the host running GDB):

	$ gdbreplay logfile host:port

Then start GDB (preferably in a different screen or window) and use the
"target" command to connect to GDBreplay:

	(gdb) target remote host:port

Repeat the same sequence of user commands to GDB that you gave in the
original debug session.  GDB should not be able to tell that it is talking
to GDBreplay rather than a real target, all other things being equal.  Note
that GDBreplay echos the command lines to stderr, as well as the contents of
the packets it sends and receives.  The last command echoed by GDBreplay is
the next command that needs to be typed to GDB to continue the session in
sync with the original session.