As a preparation for the next patch, which will move fork_inferior
from GDB to common/ (and therefore share it with gdbserver), it is
interesting to convert a few functions to C++.
This patch touches functions related to parsing command-line arguments
to the inferior (see gdb/fork-child.c:breakup_args), the way the
arguments are stored on fork_inferior (using std::vector instead of
char **), and the code responsible for dealing with argv also on
gdbserver.
I've taken this opportunity and decided to constify a few arguments to
fork_inferior/create_inferior as well, in order to make the code
cleaner. And now, on gdbserver, we're using xstrdup everywhere and
aren't checking for memory allocation failures anymore, as requested
by Pedro:
<https://sourceware.org/ml/gdb-patches/2017-03/msg00191.html>
Message-Id: <025ebdb9-90d9-d54a-c055-57ed2406b812@redhat.com>
Pedro Alves wrote:
> On the "== NULL" check: IIUC, the old NULL check was there to
> handle strdup returning NULL due to out-of-memory.
> See NULL checks and comments further above in this function.
> Now that you're using a std::vector, that doesn't work or make
> sense any longer, since if push_back fails to allocate space for
> its internal buffer (with operator new), our operator new replacement
> (common/new-op.c) calls malloc_failure, which aborts gdbserver.
>
> Not sure it makes sense to handle out-of-memory specially in
> the gdb/rsp-facing functions nowadays (maybe git blame/log/patch
> submission for that code shows some guidelines). Maybe (or, probably)
> it's OK to stop caring about it, but then we should consistently remove
> left over code, by using xstrdup instead and remove the NULL checks.
IMO this refactoring was very good to increase the readability of the
code as well, because some parts of the argument handling were
unnecessarily confusing before.
gdb/ChangeLog:
2017-04-12 Sergio Durigan Junior <sergiodj@redhat.com>
* common/common-utils.c (free_vector_argv): New function.
* common/common-utils.h: Include <vector>.
(free_vector_argv): New prototype.
* darwin-nat.c (darwin_create_inferior): Rewrite function
prototype in order to constify "exec_file" and accept a
"std::string" for "allargs".
* fork-child.c: Include <vector>.
(breakup_args): Rewrite function, using C++.
(fork_inferior): Rewrite function header, constify "exec_file_arg"
and accept "std::string" for "allargs". Update the code to
calculate "argv" based on "allargs". Update calls to "exec_fun"
and "execvp".
* gnu-nat.c (gnu_create_inferior): Rewrite function prototype in
order to constify "exec_file" and accept a "std::string" for
"allargs".
* go32-nat.c (go32_create_inferior): Likewise.
* inf-ptrace.c (inf_ptrace_create_inferior): Likewise.
* infcmd.c (run_command_1): Constify "exec_file". Use
"std::string" for inferior arguments.
* inferior.h (fork_inferior): Update prototype.
* linux-nat.c (linux_nat_create_inferior): Rewrite function
prototype in order to constify "exec_file" and accept a
"std::string" for "allargs".
* nto-procfs.c (procfs_create_inferior): Likewise.
* procfs.c (procfs_create_inferior): Likewise.
* remote-sim.c (gdbsim_create_inferior): Likewise.
* remote.c (extended_remote_run): Update code to accept
"std::string" as argument.
(extended_remote_create_inferior): Rewrite function prototype in
order to constify "exec_file" and accept a "std::string" for
"allargs".
* rs6000-nat.c (super_create_inferior): Likewise.
(rs6000_create_inferior): Likewise.
* target.h (struct target_ops) <to_create_inferior>: Likewise.
* windows-nat.c (windows_create_inferior): Likewise.
gdb/gdbserver/ChangeLog:
2017-04-12 Sergio Durigan Junior <sergiodj@redhat.com>
* server.c: Include <vector>.
<program_argv, wrapper_argv>: Convert to std::vector.
(start_inferior): Rewrite function to use C++.
(handle_v_run): Likewise. Update code that calculates the argv
based on the vRun packet; use C++.
(captured_main): Likewise.
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.