binutils-gdb/gdb/inf-ptrace.c
Andrew Burgess 200fd2874d gdb: make post_startup_inferior a virtual method on inf_ptrace_target
While working on a later patch that required me to understand how GDB
starts up inferiors, I was confused by the
target_ops::post_startup_inferior method.

The post_startup_inferior target function is only called from
inf_ptrace_target::create_inferior.

Part of the target class hierarchy looks like this:

  inf_child_target
     |
     '-- inf_ptrace_target
            |
            |-- linux_nat_target
            |
            |-- fbsd_nat_target
            |
            |-- nbsd_nat_target
            |
            |-- obsd_nat_target
            |
            '-- rs6000_nat_target

Every sub-class of inf_ptrace_target, except rs6000_nat_target,
implements ::post_startup_inferior.  The rs6000_nat_target picks up
the implementation of ::post_startup_inferior not from
inf_ptrace_target, but from inf_child_target.

No descendent of inf_child_target, outside the inf_ptrace_target
sub-tree, implements ::post_startup_inferior, which isn't really
surprising, as they would never see the method called (remember, the
method is only called from inf_ptrace_target::create_inferior).

What I find confusing is the role inf_child_target plays in
implementing, what is really a helper function for just one of its
descendents.

In this commit I propose that we formally make ::post_startup_inferior
a helper function of inf_ptrace_target.  To do this I will remove the
::post_startup_inferior from the target_ops API, and instead make this
a protected, pure virtual function on inf_ptrace_target.

I'll remove the empty implementation of ::post_startup_inferior from
the inf_child_target class, and add a new empty implementation to the
rs6000_nat_target class.

All the other descendents of inf_ptrace_target already provide an
implementation of this method and so don't need to change beyond
making the method protected within their class declarations.

To me, this makes much more sense now.  The helper function, which is
only called from within the inf_ptrace_target class, is now a part of
the inf_ptrace_target class.

The only way in which this change is visible to a user is if the user
turns on 'set debug target 1'.  With this debug flag on, prior to this
patch the user would see something like:

  -> native->post_startup_inferior (...)
  <- native->post_startup_inferior (2588939)

After this patch these lines are no longer present, as the
post_startup_inferior is no longer a top level target method.  For me,
this is an acceptable change.
2021-12-13 11:10:29 +00:00

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/* Low-level child interface to ptrace.
Copyright (C) 1988-2021 Free Software Foundation, Inc.
This file is part of GDB.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */
#include "defs.h"
#include "command.h"
#include "inferior.h"
#include "terminal.h"
#include "gdbcore.h"
#include "regcache.h"
#include "nat/gdb_ptrace.h"
#include "gdbsupport/gdb_wait.h"
#include <signal.h>
#include "inf-ptrace.h"
#include "inf-child.h"
#include "gdbthread.h"
#include "nat/fork-inferior.h"
#include "utils.h"
#include "gdbarch.h"
static PTRACE_TYPE_RET
gdb_ptrace (PTRACE_TYPE_ARG1 request, ptid_t ptid, PTRACE_TYPE_ARG3 addr,
PTRACE_TYPE_ARG4 data)
{
#ifdef __NetBSD__
return ptrace (request, ptid.pid (), addr, data);
#else
pid_t pid = get_ptrace_pid (ptid);
return ptrace (request, pid, addr, data);
#endif
}
inf_ptrace_target::~inf_ptrace_target ()
{}
/* Prepare to be traced. */
static void
inf_ptrace_me (void)
{
/* "Trace me, Dr. Memory!" */
if (ptrace (PT_TRACE_ME, 0, (PTRACE_TYPE_ARG3) 0, 0) < 0)
trace_start_error_with_name ("ptrace");
}
/* Start a new inferior Unix child process. EXEC_FILE is the file to
run, ALLARGS is a string containing the arguments to the program.
ENV is the environment vector to pass. If FROM_TTY is non-zero, be
chatty about it. */
void
inf_ptrace_target::create_inferior (const char *exec_file,
const std::string &allargs,
char **env, int from_tty)
{
inferior *inf = current_inferior ();
/* Do not change either targets above or the same target if already present.
The reason is the target stack is shared across multiple inferiors. */
int ops_already_pushed = inf->target_is_pushed (this);
target_unpush_up unpusher;
if (! ops_already_pushed)
{
/* Clear possible core file with its process_stratum. */
inf->push_target (this);
unpusher.reset (this);
}
pid_t pid = fork_inferior (exec_file, allargs, env, inf_ptrace_me, NULL,
NULL, NULL, NULL);
ptid_t ptid (pid);
/* We have something that executes now. We'll be running through
the shell at this point (if startup-with-shell is true), but the
pid shouldn't change. */
thread_info *thr = add_thread_silent (this, ptid);
switch_to_thread (thr);
unpusher.release ();
gdb_startup_inferior (pid, START_INFERIOR_TRAPS_EXPECTED);
/* On some targets, there must be some explicit actions taken after
the inferior has been started up. */
post_startup_inferior (ptid);
}
/* Clean up a rotting corpse of an inferior after it died. */
void
inf_ptrace_target::mourn_inferior ()
{
int status;
/* Wait just one more time to collect the inferior's exit status.
Do not check whether this succeeds though, since we may be
dealing with a process that we attached to. Such a process will
only report its exit status to its original parent. */
waitpid (inferior_ptid.pid (), &status, 0);
inf_child_target::mourn_inferior ();
}
/* Attach to the process specified by ARGS. If FROM_TTY is non-zero,
be chatty about it. */
void
inf_ptrace_target::attach (const char *args, int from_tty)
{
inferior *inf = current_inferior ();
/* Do not change either targets above or the same target if already present.
The reason is the target stack is shared across multiple inferiors. */
int ops_already_pushed = inf->target_is_pushed (this);
pid_t pid = parse_pid_to_attach (args);
if (pid == getpid ()) /* Trying to masturbate? */
error (_("I refuse to debug myself!"));
target_unpush_up unpusher;
if (! ops_already_pushed)
{
/* target_pid_to_str already uses the target. Also clear possible core
file with its process_stratum. */
inf->push_target (this);
unpusher.reset (this);
}
if (from_tty)
{
const char *exec_file = get_exec_file (0);
if (exec_file)
printf_unfiltered (_("Attaching to program: %s, %s\n"), exec_file,
target_pid_to_str (ptid_t (pid)).c_str ());
else
printf_unfiltered (_("Attaching to %s\n"),
target_pid_to_str (ptid_t (pid)).c_str ());
}
#ifdef PT_ATTACH
errno = 0;
ptrace (PT_ATTACH, pid, (PTRACE_TYPE_ARG3)0, 0);
if (errno != 0)
perror_with_name (("ptrace"));
#else
error (_("This system does not support attaching to a process"));
#endif
inferior_appeared (inf, pid);
inf->attach_flag = 1;
/* Always add a main thread. If some target extends the ptrace
target, it should decorate the ptid later with more info. */
thread_info *thr = add_thread_silent (this, ptid_t (pid));
switch_to_thread (thr);
/* Don't consider the thread stopped until we've processed its
initial SIGSTOP stop. */
set_executing (this, thr->ptid, true);
unpusher.release ();
}
/* Detach from the inferior. If FROM_TTY is non-zero, be chatty about it. */
void
inf_ptrace_target::detach (inferior *inf, int from_tty)
{
pid_t pid = inferior_ptid.pid ();
target_announce_detach (from_tty);
#ifdef PT_DETACH
/* We'd better not have left any breakpoints in the program or it'll
die when it hits one. Also note that this may only work if we
previously attached to the inferior. It *might* work if we
started the process ourselves. */
errno = 0;
ptrace (PT_DETACH, pid, (PTRACE_TYPE_ARG3)1, 0);
if (errno != 0)
perror_with_name (("ptrace"));
#else
error (_("This system does not support detaching from a process"));
#endif
detach_success (inf);
}
/* See inf-ptrace.h. */
void
inf_ptrace_target::detach_success (inferior *inf)
{
switch_to_no_thread ();
detach_inferior (inf);
maybe_unpush_target ();
}
/* Kill the inferior. */
void
inf_ptrace_target::kill ()
{
pid_t pid = inferior_ptid.pid ();
int status;
if (pid == 0)
return;
ptrace (PT_KILL, pid, (PTRACE_TYPE_ARG3)0, 0);
waitpid (pid, &status, 0);
target_mourn_inferior (inferior_ptid);
}
#ifndef __NetBSD__
/* See inf-ptrace.h. */
pid_t
get_ptrace_pid (ptid_t ptid)
{
pid_t pid;
/* If we have an LWPID to work with, use it. Otherwise, we're
dealing with a non-threaded program/target. */
pid = ptid.lwp ();
if (pid == 0)
pid = ptid.pid ();
return pid;
}
#endif
/* Resume execution of thread PTID, or all threads if PTID is -1. If
STEP is nonzero, single-step it. If SIGNAL is nonzero, give it
that signal. */
void
inf_ptrace_target::resume (ptid_t ptid, int step, enum gdb_signal signal)
{
PTRACE_TYPE_ARG1 request;
if (minus_one_ptid == ptid)
/* Resume all threads. Traditionally ptrace() only supports
single-threaded processes, so simply resume the inferior. */
ptid = ptid_t (inferior_ptid.pid ());
if (catch_syscall_enabled () > 0)
request = PT_SYSCALL;
else
request = PT_CONTINUE;
if (step)
{
/* If this system does not support PT_STEP, a higher level
function will have called the appropriate functions to transmute the
step request into a continue request (by setting breakpoints on
all possible successor instructions), so we don't have to
worry about that here. */
request = PT_STEP;
}
/* An address of (PTRACE_TYPE_ARG3)1 tells ptrace to continue from
where it was. If GDB wanted it to start some other way, we have
already written a new program counter value to the child. */
errno = 0;
gdb_ptrace (request, ptid, (PTRACE_TYPE_ARG3)1, gdb_signal_to_host (signal));
if (errno != 0)
perror_with_name (("ptrace"));
}
/* Wait for the child specified by PTID to do something. Return the
process ID of the child, or MINUS_ONE_PTID in case of error; store
the status in *OURSTATUS. */
ptid_t
inf_ptrace_target::wait (ptid_t ptid, struct target_waitstatus *ourstatus,
target_wait_flags options)
{
pid_t pid;
int status, save_errno;
do
{
set_sigint_trap ();
do
{
pid = waitpid (ptid.pid (), &status, 0);
save_errno = errno;
}
while (pid == -1 && errno == EINTR);
clear_sigint_trap ();
if (pid == -1)
{
fprintf_unfiltered (gdb_stderr,
_("Child process unexpectedly missing: %s.\n"),
safe_strerror (save_errno));
/* Claim it exited with unknown signal. */
ourstatus->set_signalled (GDB_SIGNAL_UNKNOWN);
return inferior_ptid;
}
/* Ignore terminated detached child processes. */
if (!WIFSTOPPED (status) && find_inferior_pid (this, pid) == nullptr)
pid = -1;
}
while (pid == -1);
*ourstatus = host_status_to_waitstatus (status);
return ptid_t (pid);
}
/* Transfer data via ptrace into process PID's memory from WRITEBUF, or
from process PID's memory into READBUF. Start at target address ADDR
and transfer up to LEN bytes. Exactly one of READBUF and WRITEBUF must
be non-null. Return the number of transferred bytes. */
static ULONGEST
inf_ptrace_peek_poke (ptid_t ptid, gdb_byte *readbuf,
const gdb_byte *writebuf,
ULONGEST addr, ULONGEST len)
{
ULONGEST n;
unsigned int chunk;
/* We transfer aligned words. Thus align ADDR down to a word
boundary and determine how many bytes to skip at the
beginning. */
ULONGEST skip = addr & (sizeof (PTRACE_TYPE_RET) - 1);
addr -= skip;
for (n = 0;
n < len;
n += chunk, addr += sizeof (PTRACE_TYPE_RET), skip = 0)
{
/* Restrict to a chunk that fits in the current word. */
chunk = std::min (sizeof (PTRACE_TYPE_RET) - skip, len - n);
/* Use a union for type punning. */
union
{
PTRACE_TYPE_RET word;
gdb_byte byte[sizeof (PTRACE_TYPE_RET)];
} buf;
/* Read the word, also when doing a partial word write. */
if (readbuf != NULL || chunk < sizeof (PTRACE_TYPE_RET))
{
errno = 0;
buf.word = gdb_ptrace (PT_READ_I, ptid,
(PTRACE_TYPE_ARG3)(uintptr_t) addr, 0);
if (errno != 0)
break;
if (readbuf != NULL)
memcpy (readbuf + n, buf.byte + skip, chunk);
}
if (writebuf != NULL)
{
memcpy (buf.byte + skip, writebuf + n, chunk);
errno = 0;
gdb_ptrace (PT_WRITE_D, ptid, (PTRACE_TYPE_ARG3)(uintptr_t) addr,
buf.word);
if (errno != 0)
{
/* Using the appropriate one (I or D) is necessary for
Gould NP1, at least. */
errno = 0;
gdb_ptrace (PT_WRITE_I, ptid, (PTRACE_TYPE_ARG3)(uintptr_t) addr,
buf.word);
if (errno != 0)
break;
}
}
}
return n;
}
/* Implement the to_xfer_partial target_ops method. */
enum target_xfer_status
inf_ptrace_target::xfer_partial (enum target_object object,
const char *annex, gdb_byte *readbuf,
const gdb_byte *writebuf,
ULONGEST offset, ULONGEST len, ULONGEST *xfered_len)
{
ptid_t ptid = inferior_ptid;
switch (object)
{
case TARGET_OBJECT_MEMORY:
#ifdef PT_IO
/* OpenBSD 3.1, NetBSD 1.6 and FreeBSD 5.0 have a new PT_IO
request that promises to be much more efficient in reading
and writing data in the traced process's address space. */
{
struct ptrace_io_desc piod;
/* NOTE: We assume that there are no distinct address spaces
for instruction and data. However, on OpenBSD 3.9 and
later, PIOD_WRITE_D doesn't allow changing memory that's
mapped read-only. Since most code segments will be
read-only, using PIOD_WRITE_D will prevent us from
inserting breakpoints, so we use PIOD_WRITE_I instead. */
piod.piod_op = writebuf ? PIOD_WRITE_I : PIOD_READ_D;
piod.piod_addr = writebuf ? (void *) writebuf : readbuf;
piod.piod_offs = (void *) (long) offset;
piod.piod_len = len;
errno = 0;
if (gdb_ptrace (PT_IO, ptid, (caddr_t)&piod, 0) == 0)
{
/* Return the actual number of bytes read or written. */
*xfered_len = piod.piod_len;
return (piod.piod_len == 0) ? TARGET_XFER_EOF : TARGET_XFER_OK;
}
/* If the PT_IO request is somehow not supported, fallback on
using PT_WRITE_D/PT_READ_D. Otherwise we will return zero
to indicate failure. */
if (errno != EINVAL)
return TARGET_XFER_EOF;
}
#endif
*xfered_len = inf_ptrace_peek_poke (ptid, readbuf, writebuf,
offset, len);
return *xfered_len != 0 ? TARGET_XFER_OK : TARGET_XFER_EOF;
case TARGET_OBJECT_UNWIND_TABLE:
return TARGET_XFER_E_IO;
case TARGET_OBJECT_AUXV:
#if defined (PT_IO) && defined (PIOD_READ_AUXV)
/* OpenBSD 4.5 has a new PIOD_READ_AUXV operation for the PT_IO
request that allows us to read the auxilliary vector. Other
BSD's may follow if they feel the need to support PIE. */
{
struct ptrace_io_desc piod;
if (writebuf)
return TARGET_XFER_E_IO;
piod.piod_op = PIOD_READ_AUXV;
piod.piod_addr = readbuf;
piod.piod_offs = (void *) (long) offset;
piod.piod_len = len;
errno = 0;
if (gdb_ptrace (PT_IO, ptid, (caddr_t)&piod, 0) == 0)
{
/* Return the actual number of bytes read or written. */
*xfered_len = piod.piod_len;
return (piod.piod_len == 0) ? TARGET_XFER_EOF : TARGET_XFER_OK;
}
}
#endif
return TARGET_XFER_E_IO;
case TARGET_OBJECT_WCOOKIE:
return TARGET_XFER_E_IO;
default:
return TARGET_XFER_E_IO;
}
}
/* Return non-zero if the thread specified by PTID is alive. */
bool
inf_ptrace_target::thread_alive (ptid_t ptid)
{
/* ??? Is kill the right way to do this? */
return (::kill (ptid.pid (), 0) != -1);
}
/* Print status information about what we're accessing. */
void
inf_ptrace_target::files_info ()
{
struct inferior *inf = current_inferior ();
printf_filtered (_("\tUsing the running image of %s %s.\n"),
inf->attach_flag ? "attached" : "child",
target_pid_to_str (inferior_ptid).c_str ());
}
std::string
inf_ptrace_target::pid_to_str (ptid_t ptid)
{
return normal_pid_to_str (ptid);
}